Note: This page contains sample records for the topic yeast mating-type switching from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: August 15, 2014.
1

The Yeast Mating-Type Switching Mechanism: A Memoir  

PubMed Central

It has been 33 years since I first presented results of genetic experiments that established the gene transposition model as the mechanism of mating-type switching in the budding yeast Saccharomyces cerevisiae at the Cold Spring Harbor Laboratory (CSHL) Yeast Genetics meeting in August 1977. Over two decades ago the Genetics Perspectives editors solicited a perspective on my participation in the studies that deciphered the mechanism of mating-type switching and revealed the phenomenon of gene silencing in yeast. Although flattered at the time, I thought that preparation of such an article called for a more seasoned researcher who had benefitted from seeing his contributions stand the test of time. Now realizing that our discovery of the transposition of a mutation from the HM? locus into the MAT (mating type) locus has provided the genetic evidence that established the gene transposition model, and having witnessed our conclusions confirmed by subsequent molecular studies, I decided that perhaps this is a good time to recount the chronology of events as they unfolded for me decades ago.

Klar, Amar J. S.

2010-01-01

2

SCFCdc4 enables mating type switching in yeast by cyclin-dependent kinase-mediated elimination of the Ash1 transcriptional repressor.  

PubMed

In the budding yeast Saccharomyces cerevisiae, mother cells switch mating types between a and ? forms, whereas daughter cells do not. This developmental asymmetry arises because the expression of the HO endonuclease, which initiates the interconversion of a and ? mating type cassettes, is extinguished by the daughter-specific Ash1 transcriptional repressor. When daughters become mothers in the subsequent cell cycle, Ash1 must be eliminated to enable a new developmental state. Here, we report that the ubiquitin ligase SCF(Cdc4) mediates the phosphorylation-dependent elimination of Ash1. The inactivation of SCF(Cdc4) stabilizes Ash1 in vivo, and consistently, Ash1 binds to and is ubiquitinated by SCF(Cdc4) in a phosphorylation-dependent manner in vitro. The mutation of a critical in vivo cyclin-dependent kinase (CDK) phosphorylation site (Thr290) on Ash1 reduces its ubiquitination and rate of degradation in vivo and decreases the frequency of mating type switching. Ash1 associates with active Cdc28 kinase in vivo and is targeted to SCF(Cdc4) in a Cdc28-dependent fashion in vivo and in vitro. Ash1 recognition by Cdc4 appears to be mediated by at least three phosphorylation sites that form two redundant diphosphorylated degrons. The phosphorylation-dependent elimination of Ash1 by the ubiquitin-proteasome system thus underpins developmental asymmetry in budding yeast. PMID:21098119

Liu, Qingquan; Larsen, Brett; Ricicova, Marketa; Orlicky, Stephen; Tekotte, Hille; Tang, Xiaojing; Craig, Karen; Quiring, Adam; Le Bihan, Thierry; Hansen, Carl; Sicheri, Frank; Tyers, Mike

2011-02-01

3

A Recombinationally Repressed Region between Mat2 and Mat3 Loci Shares Homology to Centromeric Repeats and Regulates Directionality of Mating-Type Switching in Fission Yeast  

PubMed Central

Cells of the fission yeast Schizosaccharomyces pombe switch mating type by replacing genetic information at the transcriptionally active mat1 locus with sequences copied from one of two closely linked silent loci, mat2-P or mat3-M. By a process referred to as directionality of switching, cells predominantly switch to the opposite mat1 allele; the mat1-P allele preferentially recombines with mat3, while mat1-M selects the mat2. In contrast to efficient recombination at mat1, recombination within the adjoining mat2-mat3 interval is undetectable. We defined the role of sequences between mat2 and mat3, designated the K-region, in directionality as well as recombinational suppression. Cloning and sequencing analysis revealed that a part of the K-region is homologous to repeat sequences present at centromeres, which also display transcriptional and recombinational suppression. Replacement of 7.5 kb of the K-region with the ura4(+) gene affected directionality in a variegated manner. Analysis of the swi6-mod locus, which was previously shown to affect directionality, in K?::ura4(+) strains suggested the existence of at least two overlapping directionality mechanisms. Our work furthers the model that directionality is regulated by cell-type-specific organization of the heterochromatin-like structure in the mating-type region and provides evidence that the K-region contributes to silencing of the mat2-mat3 interval.

Grewal, SIS.; Klar, AJS.

1997-01-01

4

Mating-Type Genes and MAT Switching in Saccharomyces cerevisiae  

PubMed Central

Mating type in Saccharomyces cerevisiae is determined by two nonhomologous alleles, MATa and MAT?. These sequences encode regulators of the two different haploid mating types and of the diploids formed by their conjugation. Analysis of the MATa1, MAT?1, and MAT?2 alleles provided one of the earliest models of cell-type specification by transcriptional activators and repressors. Remarkably, homothallic yeast cells can switch their mating type as often as every generation by a highly choreographed, site-specific homologous recombination event that replaces one MAT allele with different DNA sequences encoding the opposite MAT allele. This replacement process involves the participation of two intact but unexpressed copies of mating-type information at the heterochromatic loci, HML? and HMRa, which are located at opposite ends of the same chromosome-encoding MAT. The study of MAT switching has yielded important insights into the control of cell lineage, the silencing of gene expression, the formation of heterochromatin, and the regulation of accessibility of the donor sequences. Real-time analysis of MAT switching has provided the most detailed description of the molecular events that occur during the homologous recombinational repair of a programmed double-strand chromosome break.

Haber, James E.

2012-01-01

5

Deletion of the MAT-2 mating-type gene during uni-directional mating-type switching in Ceratocystis.  

PubMed

Ceratocystis eucalypti is strictly heterothallic, with single ascospore strains representing one of two opposite mating types. Most other Ceratocystis species, including C. virescens, C. pinicola, and C. fimbriata, are homothallic. In the homothallic species, the MAT-2 strains are self-fertile, while MAT-1 strains are self-sterile and grow more slowly than MAT-2 strains. The current hypothesis is that self-fertility of MAT-2 strains is due to the deletion of the MAT-2 mating-type gene, resulting in the expression of the MAT-1 mating type. These mutant MAT-1 strains are able to cross with MAT-2 strains. Part of the MAT-2 mating-type gene in C. eucalypti, C. pinicola, and C. fimbriata was amplified using degenerate primers designed from the conserved MAT-2 HMG DNA-binding motif. The expected approximately 300-bp PCR products were cloned and sequenced. Specific primers were designed that amplified 210-bp fragments only in MAT-2 isolates of C. eucalypti, C. virescens, C. pinicola, and C. finbriata. These fragments were present in self-fertile field isolates and self-fertile progeny but were absent in the self-sterile (MAT-1) progeny from selfings of C. virescens, C. pinicola, and C. fimbriata, thus supporting the hypothesis that the MAT-2 mating-type gene is deleted during uni-directional mating-type switching. A Southern-blot analysis was performed to confirm the deletion of MAT-2 gene in self-sterile progeny. The DNA sequence data for the C. eucalypti MAT-2 mating-type gene was increased to 1371-bp using TAIL-PCR and uneven PCR, representing a portion of the complete MAT-2 gene DNA sequence. PMID:10953881

Witthuhn, R C; Harrington, T C; Wingfield, B D; Steimel, J P; Wingfield, M J

2000-07-01

6

Identification of a protein that binds to the Ho endonuclease recognition sequence at the yeast mating type locus.  

PubMed Central

Mating type switching in Saccharomyces cerevisiae initiates when Ho endonuclease makes a site-specific double-stranded break at MAT, the yeast mating type locus. To identify other proteins involved in this process, we examined whether extracts prepared from ho- mutants contain additional factors that bind near the recognition sequence for Ho. Using an electrophoretic mobility shift assay, we isolated a chromatographic fraction that contains an activity, named YZbp, which binds to two sequences flanking the recognition sequence at MATalpha and to one sequence overlapping it at MATa. MAT plasmids carrying mutations in the YZbp recognition sequence are cleaved by purified Ho at wild-type efficiencies in an in vitro assay. These same plasmids, however, are not cleaved by Ho inside cells, demonstrating that YZbp acts as a positive activator of in vivo cleavage. YZbp is present in all cell types, even those not undergoing mating type switching, suggesting that it has additional cellular functions.

Wang, R; Jin, Y; Norris, D

1997-01-01

7

Regulation of Mating and Meiosis in Yeast by the Mating-Type Region  

PubMed Central

A supposed sporulation-deficient mutation of Saccharomyces cerevisiae is found to affect mating in haploids and in diploids, and to be inseparable from the mating-type locus by recombination. The mutation is regarded as a defective a allele and is designated a*. This is confirmed by its dominance relations in diploids, triploids, and tetraploids. Tetrad analysis of tetraploids and of their sporulating diploid progeny suggests the existence of an additional locus, RME, which regulates sporulation in yeast strains that can mate. Thus the recessive homozygous constitution rme/rme enables the diploids a*/?, a/a*, and ?/? to go through meiosis. Haploids carrying rme show apparent premeiotic DNA replication in sporulation conditions. This new regulatory locus is linked to the centromere of the mating-type chromosome, and its two alleles, rme and RME, are found among standard laboratory strains.

Kassir, Yona; Simchen, Giora

1976-01-01

8

Transcription of two long non-coding RNAs mediates mating type control of gametogenesis in budding yeast  

PubMed Central

Summary The cell fate decision leading to gametogenesis is essential for sexual reproduction. In S. cerevisiae, only diploid MATa/? but not haploid MATa or MAT? cells undergo gametogenesis, known as sporulation. We find that transcription of two long non-coding RNAs (lncRNAs) mediates mating type control of sporulation. In MATa or MAT? haploids expression of IME1, the central inducer of gametogenesis, is inhibited in cis by transcription of the lncRNA IRT1, located in the IME1 promoter. IRT1 transcription recruits the Set2 histone methyltransferase and the Set3 histone deacetylase complex to establish repressive chromatin at the IME1 promoter. Inhibiting expression of IRT1 and an antisense transcript that antagonizes the expression of the meiotic regulator IME4, allows cells expressing the haploid mating-type to sporulate with kinetics that are indistinguishable from that of MATa/? diploids. Conversely, expression of the two lncRNAs abolishes sporulation in MATa/? diploids. Thus, transcription of two lncRNAs governs mating type control of gametogenesis in yeast.

van Werven, Folkert J.; Neuert, Gregor; Hendrick, Natalie; Lardenois, Aurelie; Buratowski, Stephen; van Oudenaarden, Alexander; Primig, Michael; Amon, Angelika

2012-01-01

9

Characterization of two genes required for the position-effect control of yeast mating-type genes.  

PubMed Central

The mating type of haploid yeast (a or alpha) is determined by information present at the MAT locus. Identical copies of a and alpha information are present at distal loci (HMR and HML), but transcription of these copies is repressed by the action, in trans, of four unlinked genes called SIR (silent information regulator). Repression by SIR also requires, in cis, DNA sequences called E which are found to the left of HML and HMR (but not MAT) and are greater than 1 kb from the mating-type gene promoters. SIR control can act on other promoters when they are brought near the E sequence, and thus the SIR gene products act in some general manner to repress transcription. We have determined the DNA sequence of two fragments which complement mutations in the SIR2 and SIR3 genes and show that these contain the structural genes by mapping the cloned sequences onto the yeast chromosome. The SIR2 and SIR3 coding sequences were identified by constructing gene disruptions and using these mutations to replace the normal chromosomal copies. Such null mutants of both SIR2 and SIR3 are defective in the position-effect control of the silent loci but have no other detectable phenotype. We have mapped the 5' and 3' ends of the SIR2 and SIR3 mRNAs and show that their level is unaffected by mutations in any of the four known SIR complementation groups. Images Fig. 2. Fig. 3. Fig. 4.

Shore, D; Squire, M; Nasmyth, K A

1984-01-01

10

Structure and organization of transposable of transposable mating type cassettes in Saccharomyces yeasts.  

PubMed Central

Cell type in Saccharomyces yeasts is regulated by two transposable blocks of DNA, the a and alpha cassettes. There are three loci where either cassette can exist. At the HML and HMR loci the cassettes are not expressed. The cassette at the MAT locus is expressed and controls the cell type. Changes of cell type involve transposition-substitution of cassettes from HML or HMR into MAT. We recently reported the molecular cloning of the alpha cassette at the HML locus, HML alpha, and showed that it contained sequences homologous to HMR and MAT. Using HML alpha as a hybridization probe, we have isolated HMLa, HMR alpha, HMRa, MAT alpha, and MATa. Heteroduplex analysis and restriction endonuclease mapping studies indicate that the a and alpha cassettes differ by a substitution corresponding to about 750 base pairs in alpha and about 600 base pairs in a. The HML, HMR, and MAT loci have regions of homology flanking the position of the a versus alpha substitution. We have used specific chromosome rearrangements fusing MAT and HML and MAT with HMR to orient the cloned sequences on the genetic map and have found that all three genes have the same left-to-right polarity on the chromosome. Images

Strathern, J N; Spatola, E; McGill, C; Hicks, J B

1980-01-01

11

Diversity of the HO gene encoding an endonuclease for mating-type conversion in the bottom fermenting yeast Saccharomyces pastorianus.  

PubMed

Two types of HO gene were cloned, sequenced and characterized from the bottom fermenting yeast Saccharomyces pastorianus. The HO gene present on the 1500 kb chromosome was designated Sc-HO (S. cerevisiae-type HO), because the nucleotide sequence of its promoter region and the open reading frame (ORF) was almost identical to that of the S. cerevisiae laboratory strain HO gene (Lab-HO). The other HO gene, designated Lg-HO (Lager-fermenting-yeast specific HO), showed 64% and 83% homology with the promoter and ORF of the Lab-HO at the nucleotide sequence level, respectively, and was located on the 1100 kb chromosome. Analysis of the 4 kb DNA fragment amplified from S. bayanus type strain indicated that the nucleotide sequence of S. bayanus-HO is almost identical to that of the Lg-HO. The SSB1 gene located downstream of the HO gene in S. cerevisiae was also found in the 3' distal region of the Sc-HO, Lg-HO and S. bayanus HO genes. These results showed that the genetic arrangement around the HO loci both of S. pastorianus and S. bayanus is identical to S. cerevisiae. Southern analysis has revealed that Saccharomyces sensu stricto contain four types of HO genes; S. paradoxus-type HO, the Sc-HO, the Lg-HO and S. uvarum-type HO genes. This HO gene diversity provides useful information for the classification of strains belonging to Saccharomyces sensu stricto. The S. pastorianus Sc-HO, Lg-HO and S. bayanus-HO Accession Nos in the DDBJ Nucleotide Sequence Database are AB027449, AB027450 and AB027451, respectively. PMID:11015730

Tamai, Y; Tanaka, K; Umemoto, N; Tomizuka, K; Kaneko, Y

2000-10-01

12

Evidence suggesting that the ARS elements associated with silencers of the yeast mating-type locus HML do not function as chromosomal DNA replication origins.  

PubMed Central

The silent mating-type loci of Saccharomyces cerevisiae, HML and HMR, are flanked by transcriptional silencers that have ARS activity (i.e., they function as replication origins when in plasmids). To test whether these ARS elements are chromosomal origins, we mapped origins near HML (close to the left telomere of chromosome III). Our results indicate that the HML-associated ARS elements either do not function as chromosomal replication origins or do so at a frequency below our detection level, suggesting that replication from a silencer-associated origin in each S phase is not essential for the maintenance of transcriptional repression at HML. Our results also imply that the ability of a DNA fragment to function as an ARS element in a plasmid does not ensure its ability to function as an efficient chromosomal replication origin. Telomere proximity is not responsible for inactivating these ARS elements, because they are not detectably functional as chromosomal origins even in genetically modified strains in which they are far from the telomere. Images

Dubey, D D; Davis, L R; Greenfeder, S A; Ong, L Y; Zhu, J G; Broach, J R; Newlon, C S; Huberman, J A

1991-01-01

13

Basidiomycete Mating Type Genes and Pheromone Signaling?  

PubMed Central

The genome sequences of the basidiomycete Agaricomycetes species Coprinopsis cinerea, Laccaria bicolor, Schizophyllum commune, Phanerochaete chrysosporium, and Postia placenta, as well as of Cryptococcus neoformans and Ustilago maydis, are now publicly available. Out of these fungi, C. cinerea, S. commune, and U. maydis, together with the budding yeast Saccharomyces cerevisiae, have been investigated for years genetically and molecularly for signaling in sexual reproduction. The comparison of the structure and organization of mating type genes in fungal genomes reveals an amazing conservation of genes regulating the sexual reproduction throughout the fungal kingdom. In agaricomycetes, two mating type loci, A, coding for homeodomain type transcription factors, and B, encoding a pheromone/receptor system, regulate the four typical mating interactions of tetrapolar species. Evidence for both A and B mating type genes can also be identified in basidiomycetes with bipolar systems, where only two mating interactions are seen. In some of these fungi, the B locus has lost its self/nonself discrimination ability and thus its specificity while retaining the other regulatory functions in development. In silico analyses now also permit the identification of putative components of the pheromone-dependent signaling pathways. Induction of these signaling cascades leads to development of dikaryotic mycelia, fruiting body formation, and meiotic spore production. In pheromone-dependent signaling, the role of heterotrimeric G proteins, components of a mitogen-activated protein kinase (MAPK) cascade, and cyclic AMP-dependent pathways can now be defined. Additionally, the pheromone-dependent signaling through monomeric, small GTPases potentially involved in creating the polarized cytoskeleton for reciprocal nuclear exchange and migration during mating is predicted.

Raudaskoski, Marjatta; Kothe, Erika

2010-01-01

14

Corepressor-Directed Preacetylation of Histone H3 in Promoter Chromatin Primes Rapid Transcriptional Switching of Cell-Type-Specific Genes in Yeast ?  

PubMed Central

Switching between alternate states of gene transcription is fundamental to a multitude of cellular regulatory pathways, including those that govern differentiation. In spite of the progress in our understanding of such transitions in gene activity, a major unanswered question is how cells regulate the timing of these switches. Here, we have examined the kinetics of a transcriptional switch that accompanies the differentiation of yeast cells of one mating type into a distinct new cell type. We found that cell-type-specific genes silenced by the ?2 repressor in the starting state are derepressed to establish the new mating-type-specific gene expression program coincident with the loss of ?2 from promoters. This rapid derepression does not require the preloading of RNA polymerase II or a preinitiation complex but instead depends upon the Gcn5 histone acetyltransferase. Surprisingly, Gcn5-dependent acetylation of nucleosomes in the promoters of mating-type-specific genes requires the corepressor Ssn6-Tup1 even in the repressed state. Gcn5 partially acetylates the amino-terminal tails of histone H3 in repressed promoters, thereby priming them for rapid derepression upon loss of ?2. Thus, Ssn6-Tup1 not only efficiently represses these target promoters but also functions to initiate derepression by creating a chromatin state poised for rapid activation.

DeSimone, Alec M.; Laney, Jeffrey D.

2010-01-01

15

Neurospora crassa A mating-type region.  

PubMed Central

The mating-type locus of the haploid filamentous fungus Neurospora crassa is a regulatory region that controls entry into the sexual cycle and prevents formation of mixed mating-type heterokaryons in the vegetative phase. The locus consists of alternative sequences called A and a. The A mating-type DNA sequence of Neurospora crassa is composed of a region of 5301 base pairs that has little similarity to the sequence present at the mating-type locus in an a mating-type strain. However, the sequences flanking the mating-type locus in the A haploid and a haploid genome are essentially identical. The region of the A mating-type sequence required for expression of the heterokaryon incompatibility and sexual functions has been localized to a single open reading frame (ORF) encoding a polypeptide of 288 amino acids. Sequence analysis of sterile, heterokaryon-compatible mutants reveals frameshift mutations in this same ORF. The putative 288-amino acid product has a region of similarity to the MAT alpha 1 polypeptide of Saccharomyces cerevisiae. Images

Glass, N L; Grotelueschen, J; Metzenberg, R L

1990-01-01

16

Genome-Wide Gene Expression Profiling of Fertilization Competent Mycelium in Opposite Mating Types in the Heterothallic Fungus Podospora anserina  

PubMed Central

Background Mating-type loci in yeasts and ascomycotan filamentous fungi (Pezizomycotina) encode master transcriptional factors that play a critical role in sexual development. Genome-wide analyses of mating-type-specification circuits and mating-type target genes are available in Saccharomyces cerevisiae and Schizosaccharomyces pombe; however, no such analyses have been performed in heterothallic (self-incompatible) Pezizomycotina. The heterothallic fungus Podospora anserina serves as a model for understanding the basic features of mating-type control. Its mat+ and mat? mating types are determined by dissimilar allelic sequences. The mat? sequence contains three genes, designated FMR1, SMR1 and SMR2, while the mat+ sequence contains one gene, FPR1. FMR1 and FPR1 are the major regulators of fertilization, and this study presents a genome-wide view of their target genes and analyzes their target gene regulation. Methodology/Principal Findings The transcriptomic profiles of the mat+ and mat? strains revealed 157 differentially transcribed genes, and transcriptomic analysis of fmr1? and fpr1? mutant strains was used to determine the regulatory actions exerted by FMR1 and FPR1 on these differentially transcribed genes. All possible combinations of transcription repression and/or activation by FMR1 and/or FPR1 were observed. Furthermore, 10 additional mating-type target genes were identified that were up- or down-regulated to the same level in mat+ and mat? strains. Of the 167 genes identified, 32 genes were selected for deletion, which resulted in the identification of two genes essential for the sexual cycle. Interspecies comparisons of mating-type target genes revealed significant numbers of orthologous pairs, although transcriptional profiles were not conserved between species. Conclusions/Significance This study represents the first comprehensive genome-wide analysis of mating-type direct and indirect target genes in a heterothallic filamentous fungus. Mating-type transcription factors have many more target genes than are found in yeasts and exert a much greater diversity of regulatory actions on target genes, most of which are not directly related to mating.

Coppin, Evelyne; Imbeaud, Sandrine; Grognet, Pierre; Delacroix, Herve; Debuchy, Robert

2011-01-01

17

Design Principles of the Yeast G1/S Switch  

PubMed Central

A hallmark of the G1/S transition in budding yeast cell cycle is the proteolytic degradation of the B-type cyclin-Cdk stoichiometric inhibitor Sic1. Deleting SIC1 or altering Sic1 degradation dynamics increases genomic instability. Certain key facts about the parts of the G1/S circuitry are established: phosphorylation of Sic1 on multiple sites is necessary for its destruction, and both the upstream kinase Cln1/2-Cdk1 and the downstream kinase Clb5/6-Cdk1 can phosphorylate Sic1 in vitro with varied specificity, cooperativity, and processivity. However, how the system works as a whole is still controversial due to discrepancies between in vitro, in vivo, and theoretical studies. Here, by monitoring Sic1 destruction in real time in individual cells under various perturbations to the system, we provide a clear picture of how the circuitry functions as a switch in vivo. We show that Cln1/2-Cdk1 sets the proper timing of Sic1 destruction, but does not contribute to its destruction speed; thus, it acts only as a trigger. Sic1's inhibition target Clb5/6-Cdk1 controls the speed of Sic1 destruction through a double-negative feedback loop, ensuring a robust all-or-none transition for Clb5/6-Cdk1 activity. Furthermore, we demonstrate that the degradation of a single-phosphosite mutant of Sic1 is rapid and switch-like, just as the wild-type form. Our mathematical model confirms our understanding of the circuit and demonstrates that the substrate sharing between the two kinases is not a redundancy but a part of the design to overcome the trade-off between the timing and sharpness of Sic1 degradation. Our study provides direct mechanistic insight into the design features underlying the yeast G1/S switch.

Tang, Chao

2013-01-01

18

Isolates of Cryptococcus neoformans from Infected Animals Reveal Genetic Exchange in Unisexual, ? Mating Type Populations? †  

PubMed Central

Sexual reproduction and genetic exchange are important for the evolution of fungal pathogens and for producing potentially infective spores. Studies to determine whether sex occurs in the pathogenic yeast Cryptococcus neoformans var. grubii have produced enigmatic results, however: basidiospores are the most likely infective propagules, and clinical isolates are fertile and genetically diverse, consistent with a sexual species, but almost all populations examined consist of a single mating type and have little evidence for genetic recombination. The choice of population is critical when looking for recombination, particularly when significant asexual propagation is likely and when latency may complicate assessing the origin of an isolate. We therefore selected isolates from infected animals living in the region of Sydney, Australia, with the assumption that the relatively short life spans and limited travels of the animal hosts would provide a very defined population. All isolates were mating type ? and were of molecular genotype VNI or VNII. A lack of linkage disequilibrium among loci suggested that genetic exchange occurred within both genotype groups. Four diploid VNII isolates that produced filaments and basidium-like structures when cultured in proximity to an a mating type strain were found. Recent studies suggest that compatible ?-? unions can occur in C. neoformans var. neoformans populations and in populations of the sibling species Cryptococcus gattii. As a mating type strains of C. neoformans var. grubii have never been found in Australia, or in the VNII molecular type globally, the potential for ?-? unions is evidence that ?-? unisexual mating maintains sexual recombination and diversity in this pathogen and may produce infectious propagules.

Bui, Tien; Lin, Xiaorong; Malik, Richard; Heitman, Joseph; Carter, Dee

2008-01-01

19

Complementation between Phycomyces mutants of mating type (+) with abnormal phototropism  

Microsoft Academic Search

Twelve mutants ofPhycomyces blakesleeanus with defects in sporangiophore phototropism (genotypemad) were obtained from a wild type of the (+) mating type by mutagenesis with nitrosoguanidine. These mutants were tested for genetic complementation against standard (+)mad mutants derived from sexual crosses between the isogenic (+) strain and established (-)mad mutants (Ootaki et al., 1974; Eslava et al., 1976). Heterokaryons for complementation

T. Ootaki; T. Kinno; K. Yoshida; A. P. Eslava

1977-01-01

20

Localization of ASH1 mRNA Particles in Living Yeast  

Microsoft Academic Search

ASH1 mRNA localizes to the bud tip in Saccharomyces cerevisiae to establish asymmetry of HO expression, important for mating type switching. To visualize real time localization of the mRNA in living yeast cells, green fluorescent protein (GFP) was fused to the RNA-binding protein MS2 to follow a reporter mRNA containing MS2-binding sites. Formation and localization of a GFP particle in

Edouard Bertrand; Pascal Chartrand; Matthias Schaefer; Shailesh M. Shenoy; Robert H. Singer; Roy M. Long

1998-01-01

21

Selecting One of Several Mating Types through Gene Segment Joining and Deletion in Tetrahymena thermophila  

PubMed Central

The unicellular eukaryote Tetrahymena thermophila has seven mating types. Cells can mate only when they recognize cells of a different mating type as non-self. As a ciliate, Tetrahymena separates its germline and soma into two nuclei. During growth the somatic nucleus is responsible for all gene transcription while the germline nucleus remains silent. During mating, a new somatic nucleus is differentiated from a germline nucleus and mating type is decided by a stochastic process. We report here that the somatic mating type locus contains a pair of genes arranged head-to-head. Each gene encodes a mating type-specific segment and a transmembrane domain that is shared by all mating types. Somatic gene knockouts showed both genes are required for efficient non-self recognition and successful mating, as assessed by pair formation and progeny production. The germline mating type locus consists of a tandem array of incomplete gene pairs representing each potential mating type. During mating, a complete new gene pair is assembled at the somatic mating type locus; the incomplete genes of one gene pair are completed by joining to gene segments at each end of germline array. All other germline gene pairs are deleted in the process. These programmed DNA rearrangements make this a fascinating system of mating type determination.

Cervantes, Marcella D.; Hamilton, Eileen P.; Xiong, Jie; Lawson, Michael J.; Yuan, Dongxia; Hadjithomas, Michalis; Miao, Wei; Orias, Eduardo

2013-01-01

22

Dimorphic mating-type chromosomes in the fungus Microbotryum violaceum.  

PubMed

Fungi often mate as haploids, and sex chromosomes (i.e., mating-type chromosomes) that are dimorphic for their size or overall DNA content have never been reported in this kingdom. Using electrophoretic techniques for karyotype analysis, a highly dimorphic chromosome pair that determines mating compatibility is shown to occur in populations of the fungus Microbotryum violaceum. This substantiates the evolution of such dimorphism as a general feature associated with haploid determination of mating compatibility, which previously had been known only in haplodioecious plants (mosses and liverworts). Size-dimorphic sex chromosomes are present in a lineage of M. violaceum native to Europe, as well as a lineage native to North America. However, they are very different in size between these lineages, indicating either independent evolution of the dimorphism or a large degree of divergence since their isolation. Several DNA sequences that show sequence similarity to transposons were isolated from these sex chromosomes. PMID:11861552

Hood, Michael E

2002-02-01

23

Evolutionary strata in a small mating-type-specific region of the smut fungus Microbotryum violaceum.  

PubMed

DNA sequence analysis and genetic mapping of loci from mating-type-specific chromosomes of the smut fungus Microbotryum violaceum demonstrated that the nonrecombining mating-type-specific region in this species comprises approximately 25% ( approximately 1 Mb) of the chromosome length. Divergence between homologous mating-type-linked genes in this region varies between 0 and 8.6%, resembling the evolutionary strata of vertebrate and plant sex chromosomes. PMID:19448270

Votintseva, Antonina A; Filatov, Dmitry A

2009-08-01

24

Evolutionary Strata in a Small Mating-Type-Specific Region of the Smut Fungus Microbotryum violaceum  

PubMed Central

DNA sequence analysis and genetic mapping of loci from mating-type-specific chromosomes of the smut fungus Microbotryum violaceum demonstrated that the nonrecombining mating-type-specific region in this species comprises ?25% (?1 Mb) of the chromosome length. Divergence between homologous mating-type-linked genes in this region varies between 0 and 8.6%, resembling the evolutionary strata of vertebrate and plant sex chromosomes.

Votintseva, Antonina A; Filatov, Dmitry A.

2009-01-01

25

Maintaining Two Mating Types: Structure of the Mating Type Locus and Its Role in Heterokaryosis in Podospora anserina.  

PubMed

Pseudo-homothallism is a reproductive strategy elected by some fungi producing heterokaryotic sexual spores containing genetically different but sexually compatible nuclei. This lifestyle appears as a compromise between true homothallism (self-fertility with predominant inbreeding) and complete heterothallism (with exclusive outcrossing). However, pseudohomothallic species face the problem of maintaining heterokaryotic mycelia to fully benefit from this lifestyle, as homokaryons are self-sterile. Here, we report on the structure of chromosome 1 in mat+ and mat- isolates of strain S of the pseudohomothallic fungus Podospora anserina. Chromosome 1 contains either one of the mat+ and mat- mating types of P. anserina, which is mostly found in nature as a mat+/mat- heterokaryotic mycelium harboring sexually compatible nuclei. We identified a "mat" region ?0.8 Mb long, devoid of meiotic recombination and containing the mating-type idiomorphs, which is a candidate to be involved in the maintenance of the heterokaryotic state, since the S mat+ and S mat- strains have different physiology that may enable hybrid-vigor-like phenomena in the heterokaryons. The mat region contains 229 coding sequences. A total of 687 polymorphisms were detected between the S mat+ and S mat- chromosomes. Importantly, the mat region is colinear between both chromosomes, which calls for an original mechanism of recombination inhibition. Microarray analyses revealed that 10% of the P. anserina genes have different transcriptional profiles in S mat+ and S mat-, in line with their different phenotypes. Finally, we show that the heterokaryotic state is faithfully maintained during mycelium growth of P. anserina, yet mat+/mat+ and mat-/mat- heterokaryons are as stable as mat+/mat- ones, evidencing a maintenance of heterokaryosis that does not rely on fitness-enhancing complementation between the S mat+ and S mat- strains. PMID:24558260

Grognet, Pierre; Bidard, Frédérique; Kuchly, Claire; Tong, Laetitia Chan Ho; Coppin, Evelyne; Benkhali, Jinane Ait; Couloux, Arnaud; Wincker, Patrick; Debuchy, Robert; Silar, Philippe

2014-05-01

26

Genetic Variability and Distribution of Mating Type Alleles in Field Populations of Leptosphaeria maculans from France  

Microsoft Academic Search

scales (leaf, 2-m2 field plot, and field) enabling the evaluation of spatial distribution of the mating type alleles and of genetic variability within and among field populations. Within each field population, no gametic disequilibrium between the minisatellite loci was detected and the mating type alleles were present at equal frequencies. Both sexual and asexual reproduction occur in the field, but

Lilian Gout; Maria Eckert; Thierry Rouxel; Marie-Helene Balesdent

2006-01-01

27

A nutrient dependant switch explains mutually exclusive existence of meiosis and mitosis initiation in budding yeast.  

PubMed

Nutrients from living environment are vital for the survival and growth of any organism. Budding yeast diploid cells decide to grow by mitosis type cell division or decide to create unique, stress resistant spores by meiosis type cell division depending on the available nutrient conditions. To gain a molecular systems level understanding of the nutrient dependant switching between meiosis and mitosis initiation in diploid cells of budding yeast, we develop a theoretical model based on ordinary differential equations (ODEs) including the mitosis initiator and its relations to budding yeast meiosis initiation network. Our model accurately and qualitatively predicts the experimentally revealed temporal variations of related proteins under different nutrient conditions as well as the diverse mutant studies related to meiosis and mitosis initiation. Using this model, we show how the meiosis and mitosis initiators form an all-or-none type bistable switch in response to available nutrient level (mainly nitrogen). The transitions to and from meiosis or mitosis initiation states occur via saddle node bifurcation. This bidirectional switch helps the optimal usage of available nutrients and explains the mutually exclusive existence of meiosis and mitosis pathways. PMID:24099720

Wannige, C T; Kulasiri, D; Samarasinghe, S

2014-01-21

28

Mating type gene analysis in apparently asexual Cercospora species is suggestive of cryptic sex.  

PubMed

The genus Cercospora consists of numerous important, apparently asexual plant pathogens. We designed degenerate primers from homologous sequences in related species to amplify part of the C. apii, C. apiicola, C. beticola, C. zeae-maydis and C. zeina mating type genes. Chromosome walking was used to determine the full length mating type genes of these species. Primers were developed to amplify and sequence homologous portions of the mating type genes of additional species. Phylogenetic analyses of these sequences revealed little variation among members of the C. apii complex, whereas C. zeae-maydis and C. zeina were found to be dissimilar. The presence of both mating types in approximately even proportions in C. beticola, C. zeae-maydis and C. zeina populations, in contrast to single mating types in C. apii (MAT1) and C. apiicola (MAT2), suggests that a sexual cycle may be active in some of these species. PMID:16839791

Groenewald, Marizeth; Groenewald, Johannes Z; Harrington, Thomas C; Abeln, Edwin C A; Crous, Pedro W

2006-12-01

29

Development of a PCR-based mating-type assay for Clavicipitaceae.  

PubMed

This study developed a PCR-based mating-type assay for Clavicipitaceae. PCR primer sets for the mating-type genes MAT1-1-1 and MAT1-2-1 were designed based on the amino acid sequences of the conserved alpha and HMG boxes, respectively. The PCR-based mating-type assay could be applied for various clavicipitaceous genera (Balansia, Claviceps, Cordyceps and Epichloë). Most of the clavicipitaceous fungi possessed either MAT1-1-1 or MAT1-2-1, and were supposed to be heterothallic. Although the PCR products obtained by the mating-type assay were short, the phylogenetic trees of the mating-type genes gave better resolutions than that of 18S rDNA and agreed well to their econutritional modes. PMID:15321663

Yokoyama, Eiji; Yamagishi, Kenzo; Hara, Akira

2004-08-15

30

Tuber melanosporum: mating type distribution in a natural plantation and dynamics of strains of different mating types on the roots of nursery-inoculated host plants.  

PubMed

• In light of the recent finding that Tuber melanosporum, the ectomycorrhizal ascomycete that produces the most highly prized black truffles, is a heterothallic species, we monitored the spatial distribution of strains with opposite mating types (MAT) in a natural truffle ground and followed strain dynamics in artificially inoculated host plants grown under controlled conditions. • In a natural truffle ground, ectomycorrhizas (ECMs), soil samples and fruit bodies were sampled and genotyped to determine mating types. Simple sequence repeat (SSR) markers were also used to fingerprint ECMs and fruit bodies. The ECMs from nursery-inoculated host plants were analysed for mating type at 6 months and 19 months post-inoculation. • In open-field conditions, all ECMs from the same sampling site showed an identical mating type and an identical haploid genotype, based on SSR analysis. Interestingly, the gleba of fruit bodies always demonstrated the same genotype as the surrounding ECMs. Although root tips from nursery-grown plants initially developed ECMs of both mating types, a dominance of ECMs of the same MAT were found after several months. • The present study deepens our understanding of the vegetative and sexual propagation modes of T. melanosporum. These results are highly relevant for truffle cultivation. PMID:20964691

Rubini, Andrea; Belfiori, Beatrice; Riccioni, Claudia; Arcioni, Sergio; Martin, Francis; Paolocci, Francesco

2011-02-01

31

Potato late blight in Morocco: characterization of Phytophthora infestans populations (virulence and mating type).  

PubMed

Late blight caused by Phytophthora infestans, is the most important disease of potato in Morocco. Use of partially resistant cultivars should be an essential component of a sustainable management strategy of potato late blight, provided the durability of this form of resistance. It is therefore important to determine the nature of P. infestans Moroccan populations. Mating types were determined for 91 strains of P. infestans collected in the northern (Larache-northern plain), north western (Kénitra) and north eastern (Méknès, Middle Atlas) potato cropping areas of Morocco in 1999-2000, 2000-2001 and 2003-2004. They showed a clear regional structure of these populations, with the presence of both mating types (A1 and A2). Of all isolates collected since 1999, A2 mating type constituted 56% (54 isolates), following by A1 mating type (40.7%, 31 isolates) and A1-A2 (self-fertile) mating type (3.30%, 3 isolates). Populations from Méknès and Kénitra consisted mainly of A2 mating type, whereas populations from Larache predominantly included A1 mating type. Physiological race study revealed the presence of 19 races of P. infestans in the first collection of 25 isolates tested between 1999 and 2001. All known virulence genes were detected in western and northern Moroccan isolates, except virulence for resistance genes R2, R5, and R6 which were absent. All isolates were able to overcome two or more R genes except one isolate (5-1) corresponding to race 1. PMID:16637185

Achbani, E H; Hafidi, M; Abdellatif, B; Lamaaraf, N; Kouta, B; Nafie, N; Corbière, R; Andrivon, D

2005-01-01

32

Evidence of Recombination in Mixed-Mating-Type and ?-Only Populations of Cryptococcus gattii Sourced from Single Eucalyptus Tree Hollows?  

PubMed Central

Disease caused by the pathogenic yeast Cryptococcus gattii begins with the inhalation of an infectious propagule. As C. gattii is heavily encapsulated, this propagule is most likely to be a basidiospore. However, most C. gattii strains are infertile in laboratory crosses, and population studies indicate that recombination and dispersal are very restricted. In addition, strains of the ? mating type predominate, which would not be expected in a mating population. C. gattii comprises four genetically distinct molecular genotypes, designated VGI to VGIV. C. gattii molecular type VGI has a strong association with Eucalyptus camaldulensis and can be found in high numbers in E. camaldulensis hollows. Previous work on isolates obtained from E. camaldulensis suggested that environmental populations of C. gattii are highly fragmented, have limited ability to disperse, and are confined to individual tree hollows. In the current study, we examined large numbers of isolates from three separate hollows for evidence of recombination. In two hollows, the ? and a mating types were present in approximately equal numbers. The third hollow had ? cells only and was from a region where a isolates have never been found. Statistical analysis of multilocus genotypes revealed recombining subpopulations in the three Eucalyptus hollows. Recombination was equally present in the ?-a and ?-only populations. This is consistent with recent studies that have found evidence suggestive of ?-? mating in C. gattii and Cryptococcus neoformans and raises the possibility this may be a widespread phenomenon, allowing these fungi to recombine despite a paucity of a mating partners.

Saul, Nathan; Krockenberger, Mark; Carter, Dee

2008-01-01

33

Deletion of the Cochliobolus heterostrophus mating-type ( MAT ) locus promotes the function of MAT transgenes  

Microsoft Academic Search

Cochhobolus heterostrophus has alternate genes (MAT-1 andMAT-2) at its mating-type locus. Transformants of aMAT-1 or aMAT-2 strain carrying a transgene of opposite mating type can self and are dual maters; the transgene, however, promotes development of pseudothecia only, not ascospores. To determine if the resident gene interferes with the function of the transgene, transformation vectors were designed to delete different

Stefan Wirsel; B. Gillian Turgeon; O. C. Yoder

1996-01-01

34

Deletion of the Cochliobolus heterostrophus mating-type ( MAT ) locus promotes the function of MAT transgenes  

Microsoft Academic Search

Cochliobolus heterostrophus has alternate genes (MAT-1 and MAT-2) at its mating-type locus. Transformants of a MAT-1 or a MAT-2 strain carrying a transgene of opposite mating type can self and are dual maters; the transgene, however, promotes development of pseudothecia only, not ascospores. To determine if the resident gene interferes with the function of the transgene, transformation vectors were designed

Stefan Wirsel; B. Gillian Turgeon; O. C. Yoder

1996-01-01

35

Differentiation between Atypical Isolates of Candida lusitaniae and Candida pulcherrima by Determination of Mating Type  

PubMed Central

We report on five clinical isolates routinely identified as Candida lusitaniae that the ID 32C system was unable to discriminate from the closely related species Candida pulcherrima. When additional tests did not allow accurate identification, the less usual mating type test identified all of them as Clavispora lusitaniae. Mating type testing appears to be a valuable tool for assessing the true incidence of this emerging non-albicans Candida species.

Noel, Thierry; Favel, Anne; Michel-Nguyen, Annie; Goumar, Abdelhak; Fallague, Karim; Chastin, Christiane; Leclerc, Florence; Villard, Jean

2005-01-01

36

Pseudohomothallism and Evolution of the Mating-Type Chromosome in Neurospora Tetrasperma  

PubMed Central

Ascospores of Neurospora tetrasperma normally contain nuclei of both mating-type idiomorphs (a and A), resulting in self-fertile heterokaryons (a type of sexual reproduction termed pseudohomothallism). Occasional homokaryotic self-sterile strains (either a or A) behave as heterothallics and, in principle, provide N. tetrasperma with a means for facultative outcrossing. This study was conceived as an investigation of the population biology of N. tetrasperma to assess levels of intrastrain heterokaryosis (heterozygosity). The unexpected result was that the mating-type chromosome and autosomes exhibited very different patterns of evolution, apparently because of suppressed recombination between mating-type chromosomes. Analysis of sequences on the mating-type chromosomes of wild-collected self-fertile strains revealed high levels of genetic variability between sibling A and a nuclei. In contrast, sequences on autosomes of sibling A and a nuclei exhibited nearly complete homogeneity. Conservation of distinct haplotype combinations on A and a mating-type chromosomes in strains from diverse locations further suggested an absence of recombination over substantial periods of evolutionary time. The suppression of recombination on the N. tetrasperma mating-type chromosome, expected to ensure a high frequency of self fertility, presents an interesting parallel with, and possible model for studying aspects of, the evolution of mammalian sex chromosomes.

Merino, S. T.; Nelson, M. A.; Jacobson, D. J.; Natvig, D. O.

1996-01-01

37

Mating-Type Locus of Cryptococcus neoformans: a Step in the Evolution of Sex Chromosomes  

PubMed Central

The sexual development and virulence of the fungal pathogen Cryptococcus neoformans is controlled by a bipolar mating system determined by a single locus that exists in two alleles, ? and a. The ? and a mating-type alleles from two divergent varieties were cloned and sequenced. The C. neoformans mating-type locus is unique, spans >100 kb, and contains more than 20 genes. MAT-encoded products include homologs of regulators of sexual development in other fungi, pheromone and pheromone receptors, divergent components of a MAP kinase cascade, and other proteins with no obvious function in mating. The ? and a alleles of the mating-type locus have extensively rearranged during evolution and strain divergence but are stable during genetic crosses and in the population. The C. neoformans mating-type locus is strikingly different from the other known fungal mating-type loci, sharing features with the self-incompatibility systems and sex chromosomes of algae, plants, and animals. Our study establishes a new paradigm for mating-type loci in fungi with implications for the evolution of cell identity and self/nonself recognition.

Lengeler, Klaus B.; Fox, Deborah S.; Fraser, James A.; Allen, Andria; Forrester, Keri; Dietrich, Fred S.; Heitman, Joseph

2002-01-01

38

Molecular characterization of tol, a mediator of mating-type-associated vegetative incompatibility in Neurospora crassa.  

PubMed Central

The mating-type locus in the haploid filamentous fungus, Neurospora crassa, controls mating and sexual development. The fusion of reproductive structures of opposite mating type, A and a, is required to initiate sexual reproduction. However, the fusion of hyphae of opposite mating type during vegetative growth results in growth inhibition and cell death, a process that is mediated by the tol locus. Mutations in tol are recessive and suppress mating-type-associated heterokaryon incompatibility. In this study, we describe the cloning and characterization of tol. The tol gene encodes a putative 1011-amino-acid polypeptide with a coiled-coil domain and a leucine-rich repeat. Both regions are required for tol activity. Repeat-induced point mutations in tol result in mutants that are wild type during vegetative growth and sexual reproduction, but that allow opposite mating-type individuals to form a vigorous heterokaryon. Transcript analyses show that tol mRNA is present during vegetative growth but absent during a cross. These data suggest that tol transcription is repressed to allow the coexistence of opposite mating-type nuclei during the sexual reproductive phase. tol is expressed in a mat A, mat a, A/a partial diploid and in a mating-type deletion strain, indicating that MAT A-1 and MAT a-1 are not absolutely required for transcription or repression of tol. These data suggest that TOL may rather interact with MAT A-1 and/or MAT a-1 (or downstream products) to form a death-triggering complex.

Shiu, P K; Glass, N L

1999-01-01

39

Structure and function of a mating-type gene from the homothallic species Neurospora africana.  

PubMed

The homothallic Neurospora species, N. africana, contains sequences that hybridize to the A but not to a mating-type sequences of the heterothallic species N. crassa. In this study, the N. africana mating-type gene, mt A-1, was cloned, sequenced and its function analyzed in N. crassa. Although N. africana does not mate in a heterothallic manner, its mt A-1 gene functions as a mating activator in N. crassa. In addition, the N. africana mt A-1 gene confers mating type-associated vegetative incompatibility in N. crassa. DNA sequence analysis shows that the N. africana mt A-1 open reading frame (ORF) is 93% identical to that of N. crassa mt A-1. The mt A-1 ORF of N. africana contains no stop codons and was detected as a cDNA which is processed in a similar manner to mt A-1 of N. crassa. By DNA blot and orthogonal field agarose gel electrophoretic analysis, it is shown that the composition and location of the mating-type locus and the organization of the mating-type chromosome of N. africana are similar to that of N. crassa. PMID:8078466

Glass, N L; Smith, M L

1994-08-15

40

Both mating types of the wheat pathogen Mycosphaerella graminicola are present in Morocco.  

PubMed

Septoria tritici blotch caused by the heterothallic ascomycete Mycosphaerella graminicola is one of the most currently damaging diseases on wheat crops worldwide. So far, no information was reported about the status of sexual reproduction of this pathogen under Moroccan conditions. We investigated here for the first time the occurrence of the two mating types (MAT1-1 and MAT1-2) of M. graminicola in Morocco by sampling 141 single-conidial isolates from 4 important wheat producing regions (Gharb, Saïs, Chaouia and Tadla). The mating type of each isolate was determined by amplification with multiplex PCR of a partial sequence from the corresponding idiomorph. Overall, 43% out of the assessed isolates were MAT1-1 and 57 % were MAT1-2. Both mating types were identified within the 3 sampled regions Gharb, Saïs and Chaouia, but not in Tadla, where only MAT1-2 isolates were found. The presence of the two mating types highlighted here offers a suitable genetic condition for M. graminicola to occur sexual reproduction in Morocco. The potential of sexual recombination will be examined by the study of mating type frequencies using a large sample size as well as by searching and quantification of pseudothecia in the field. PMID:21534472

Elbekali, A Y; Ramdani, A; Tisserant, B; Deweer, C; Siah, A; Reignault, Ph; Halama, P

2010-01-01

41

The Clr7 and Clr8 Directionality Factors and the Pcu4 Cullin Mediate Heterochromatin Formation in the Fission Yeast Schizosaccharomyces pombe  

PubMed Central

Fission yeast heterochromatin is formed at centromeres, telomeres, and in the mating-type region where it mediates the transcriptional silencing of the mat2-P and mat3-M donor loci and the directionality of mating-type switching. We conducted a genetic screen for directionality mutants. This screen revealed the essential role of two previously uncharacterized factors, Clr7 and Clr8, in heterochromatin formation. Clr7 and Clr8 are required for localization of the Swi6 chromodomain protein and for histone H3 lysine 9 methylation, thereby influencing not only mating-type switching but also transcriptional silencing in all previously characterized heterochromatic regions, chromosome segregation, and meiotic recombination in the mating-type region. We present evidence for physical interactions between Clr7 and the mating-type region and between Clr7 and the S. pombe cullin Pcu4, indicating that a complex containing these proteins mediates an early step in heterochromatin formation and implying a role for ubiquitination at this early stage prior to the action of the Clr4 histone methyl-transferase. Like Clr7 and Clr8, Pcu4 is required for histone H3 lysine 9 methylation, and bidirectional centromeric transcripts that are normally processed into siRNA by the RNAi machinery in wild-type cells are easily detected in cells lacking Clr7, Clr8, or Pcu4. Another physical interaction, between the nucleoporin Nup189 and Clr8, suggests that Clr8 might be involved in tethering heterochromatic regions to the nuclear envelope by association with the nuclear-pore complex.

Thon, Genevieve; Hansen, Klavs R.; Altes, Susagna Padrissa; Sidhu, Deepak; Singh, Gurjeet; Verhein-Hansen, Janne; Bonaduce, Michael J.; Klar, Amar J. S.

2005-01-01

42

Female fertility and mating type distribution in a Philippine population of Fusarium verticillioides.  

PubMed

Fusarium verticillioides is a common causal agent of maize ear rot in the Philippines. Eighty isolates were collected from healthy and infected maize cobs from Laguna province. Fifty isolates crossed with one of the mating type A testers. The ratio of MATA-1:MATA-2 is 27:23, which follows a Mendelian ratio of 1:1. The effective population number, Ne, was determined by mating type and male/hermaphrodite polymorphisms. The effective population number for mating type, Ne mt, is 81% of the count (total population), and that for male/hermaphrodite status, Ne f, is 36-42% of the count (total population). Sexual reproduction in Philippine isolates of F. verticillioides does not occur frequently, compared to F. verticillioides in other regions of the world. PMID:18263979

Cumagun, Christian Joseph R

2008-01-01

43

Mating type gene (MAT1-1) in Japanese isolates of Trichophyton rubrum.  

PubMed

Trichophyton rubrum is an anthropophilic species that is the most frequent etiologic agent of human dermatophytosis throughout the world. No teleomorph has been identified for T. rubrum strains. This study used PCR analysis to confirm the presence of a mating type locus in the genome of Japanese isolates of T. rubrum. To clarify the epidemiological and ecological characteristics of this fungus, mating type sequences were tested for correlation of MAT genotype to mating type. This study examined clinical isolates of T. rubrum that had been obtained from 206 human cases of tinea pedis and tinea unguium in Japan, including those from Fukuoka (29 strains), Gifu (23 strains), Kanazawa (63 strains), and Tokyo (91 strains), along with 10 isolates derived from 10 cases of canine dermatophytosis. PCR detected the presence of MAT1-1 in all of the human and animal isolates. Therefore, all isolates examined were expected to react as (-) type on the mating test and not as (+) type. PMID:23212652

Kano, Rui; Isizuka, Maiko; Hiruma, Masataro; Mochizuki, Takashi; Kamata, Hiroshi; Hasegawa, Atsuhiko

2013-02-01

44

Evolution of Sexes from an Ancestral Mating-Type Specification Pathway  

PubMed Central

Male and female sexes have evolved repeatedly in eukaryotes but the origins of dimorphic sexes and their relationship to mating types in unicellular species are not understood. Volvocine algae include isogamous species such as Chlamydomonas reinhardtii, with two equal-sized mating types, and oogamous multicellular species such as Volvox carteri with sperm-producing males and egg-producing females. Theoretical work predicts genetic linkage of a gamete cell-size regulatory gene(s) to an ancestral mating-type locus as a possible step in the evolution of dimorphic gametes, but this idea has not been tested. Here we show that, contrary to predictions, a single conserved mating locus (MT) gene in volvocine algae—MID, which encodes a RWP-RK domain transcription factor—evolved from its ancestral role in C. reinhardtii as a mating-type specifier, to become a determinant of sperm and egg development in V. carteri. Transgenic female V. carteri expressing male MID produced functional sperm packets during sexual development. Transgenic male V. carteri with RNA interference (RNAi)-mediated knockdowns of VcMID produced functional eggs, or self-fertile hermaphrodites. Post-transcriptional controls were found to regulate cell-type–limited expression and nuclear localization of VcMid protein that restricted its activity to nuclei of developing male germ cells and sperm. Crosses with sex-reversed strains uncoupled sex determination from sex chromosome identity and revealed gender-specific roles for male and female mating locus genes in sexual development, gamete fitness and reproductive success. Our data show genetic continuity between the mating-type specification and sex determination pathways of volvocine algae, and reveal evidence for gender-specific adaptations in the male and female mating locus haplotypes of Volvox. These findings will enable a deeper understanding of how a master regulator of mating-type determination in an ancestral unicellular species was reprogrammed to control sexually dimorphic gamete development in a multicellular descendant.

Geng, Sa; De Hoff, Peter; Umen, James G.

2014-01-01

45

Identification of the Mating-Type (MAT) Locus That Controls Sexual Reproduction of Blastomyces dermatitidis  

PubMed Central

Blastomyces dermatitidis is a dimorphic fungal pathogen that primarily causes blastomycosis in the midwestern and northern United States and Canada. While the genes controlling sexual development have been known for a long time, the genes controlling sexual reproduction of B. dermatitidis (teleomorph, Ajellomyces dermatitidis) are unknown. We identified the mating-type (MAT) locus in the B. dermatitidis genome by comparative genomic approaches. The B. dermatitidis MAT locus resembles those of other dimorphic fungi, containing either an alpha-box (MAT1-1) or an HMG domain (MAT1-2) gene linked to the APN2, SLA2, and COX13 genes. However, in some strains of B. dermatitidis, the MAT locus harbors transposable elements (TEs) that make it unusually large compared to the MAT locus of other dimorphic fungi. Based on the MAT locus sequences of B. dermatitidis, we designed specific primers for PCR determination of the mating type. Two B. dermatitidis isolates of opposite mating types were cocultured on mating medium. Immature sexual structures were observed starting at 3 weeks of coculture, with coiled-hyphae-containing cleistothecia developing over the next 3 to 6 weeks. Genetic recombination was detected in potential progeny by mating-type determination, PCR-restriction fragment length polymorphism (PCR-RFLP), and random amplification of polymorphic DNA (RAPD) analyses, suggesting that a meiotic sexual cycle might have been completed. The F1 progeny were sexually fertile when tested with strains of the opposite mating type. Our studies provide a model for the evolution of the MAT locus in the dimorphic and closely related fungi and open the door to classic genetic analysis and studies on the possible roles of mating and mating type in infection and virulence.

Li, Wenjun; Sullivan, Thomas D.; Walton, Eric; Averette, Anna Floyd; Sakthikumar, Sharadha; Cuomo, Christina A.; Klein, Bruce S.

2013-01-01

46

Evolution of sexes from an ancestral mating-type specification pathway.  

PubMed

Male and female sexes have evolved repeatedly in eukaryotes but the origins of dimorphic sexes and their relationship to mating types in unicellular species are not understood. Volvocine algae include isogamous species such as Chlamydomonas reinhardtii, with two equal-sized mating types, and oogamous multicellular species such as Volvox carteri with sperm-producing males and egg-producing females. Theoretical work predicts genetic linkage of a gamete cell-size regulatory gene(s) to an ancestral mating-type locus as a possible step in the evolution of dimorphic gametes, but this idea has not been tested. Here we show that, contrary to predictions, a single conserved mating locus (MT) gene in volvocine algae-MID, which encodes a RWP-RK domain transcription factor-evolved from its ancestral role in C. reinhardtii as a mating-type specifier, to become a determinant of sperm and egg development in V. carteri. Transgenic female V. carteri expressing male MID produced functional sperm packets during sexual development. Transgenic male V. carteri with RNA interference (RNAi)-mediated knockdowns of VcMID produced functional eggs, or self-fertile hermaphrodites. Post-transcriptional controls were found to regulate cell-type-limited expression and nuclear localization of VcMid protein that restricted its activity to nuclei of developing male germ cells and sperm. Crosses with sex-reversed strains uncoupled sex determination from sex chromosome identity and revealed gender-specific roles for male and female mating locus genes in sexual development, gamete fitness and reproductive success. Our data show genetic continuity between the mating-type specification and sex determination pathways of volvocine algae, and reveal evidence for gender-specific adaptations in the male and female mating locus haplotypes of Volvox. These findings will enable a deeper understanding of how a master regulator of mating-type determination in an ancestral unicellular species was reprogrammed to control sexually dimorphic gamete development in a multicellular descendant. PMID:25003332

Geng, Sa; De Hoff, Peter; Umen, James G

2014-07-01

47

A heritable switch in carbon source utilization driven by an unusual yeast prion.  

PubMed

Several well-characterized fungal proteins act as prions, proteins capable of multiple conformations, each with different activities, at least one of which is self-propagating. Through such self-propagating changes in function, yeast prions act as protein-based elements of phenotypic inheritance. We report a prion that makes cells resistant to the glucose-associated repression of alternative carbon sources, [GAR(+)] (for "resistant to glucose-associated repression," with capital letters indicating dominance and brackets indicating its non-Mendelian character). [GAR(+)] appears spontaneously at a high rate and is transmissible by non-Mendelian, cytoplasmic inheritance. Several lines of evidence suggest that the prion state involves a complex between a small fraction of the cellular complement of Pma1, the major plasma membrane proton pump, and Std1, a much lower-abundance protein that participates in glucose signaling. The Pma1 proteins from closely related Saccharomyces species are also associated with the appearance of [GAR(+)]. This allowed us to confirm the relationship between Pma1, Std1, and [GAR(+)] by establishing that these proteins can create a transmission barrier for prion propagation and induction in Saccharomyces cerevisiae. The fact that yeast cells employ a prion-based mechanism for heritably switching between distinct carbon source utilization strategies, and employ the plasma membrane proton pump to do so, expands the biological framework in which self-propagating protein-based elements of inheritance operate. PMID:19797769

Brown, Jessica C S; Lindquist, Susan

2009-10-01

48

A Mendelian Mutation Affecting Mating-Type Determination Also Affects Developmental Genomic Rearrangements in Paramecium Tetraurelia  

PubMed Central

In Paramecium tetraurelia, mating type is determined during the differentiation of the somatic macronucleus from a zygotic nucleus genetically competent for both types, O and E. Determination of the developing macronucleus is controlled by the parental macronucleus through an unknown mechanism resulting in the maternal inheritance of mating types. The pleiotropic mutation mtF(E) affects macronuclear differentiation. Determination for E is constitutive in mutant homozygotes; a number of unrelated mutant characters are also acquired during development. We have examined the possibility that the mutation causes a defect in the developmental rearrangements of the germ-line genome. We show that the excision of an IES (internal eliminated sequence) interrupting the coding sequence of a surface antigen gene is impaired in the mutant, resulting in an alternative macronuclear version of the gene. Once established, the excision defect is indefinitely transmitted across sexual generations in the cytoplasmic lineage, even in a wild-type genetic context. Thus, the processes of mating-type determination and excision of this IES, in addition to their common sensitivity to the mtF(E) mutation, show a similar maternal inheritance of developmental alternatives in wild-type cells, suggesting a molecular model for mating-type determination.

Meyer, E.; Keller, A. M.

1996-01-01

49

Extensive Divergence Between Mating-Type Chromosomes of the Anther-Smut Fungus  

PubMed Central

Genomic regions that determine mating compatibility are subject to distinct evolutionary forces that can lead to a cessation of meiotic recombination and the accumulation of structural changes between members of the homologous chromosome pair. The relatively recent discovery of dimorphic mating-type chromosomes in fungi can aid the understanding of sex chromosome evolution that is common to dioecious plants and animals. For the anther-smut fungus, Microbotryum lychnidis-dioicae (= M. violaceum isolated from Silene latifolia), the extent of recombination cessation on the dimorphic mating-type chromosomes has been conflictingly reported. Comparison of restriction digest optical maps for the two mating-type chromosomes shows that divergence extends over 90% of the chromosome lengths, flanked at either end by two pseudoautosomal regions. Evidence to support the expansion of recombination cessation in stages from the mating-type locus toward the pseudoautosomal regions was not found, but evidence of such expansion could be obscured by ongoing processes that affect genome structure. This study encourages the comparison of forces that may drive large-scale recombination suppression in fungi and other eukaryotes characterized by dimorphic chromosome pairs associated with sexual life cycles.

Hood, Michael E.; Petit, Elsa; Giraud, Tatiana

2013-01-01

50

The Mating-Type-Related Bias of Gene Conversion in Schizosaccharomyces pombe  

PubMed Central

The mating-type bias (mat-bias) of gene conversion was previously described as a phenomenon in which the number of prototrophic recombinants in an ura4A heteroallelic two-factor cross relates to the mating types of the parents. We show now that the mat-bias is restricted neither to ura4A nor to recombination hotspots, but occurs at other genomic loci, too. It is specific for gene conversion and absent in azygotic meiosis. Thus, the mat-bias must originate from mating-type-specific “imprinting” events before karyogamy takes place. Structural variations of the mating-type locus, such as h+N, h+S, h?S, h+smt?, or h?smt?, showed mat-bias manifestation. Mutations in genes coding for histone acetylase (gcn5, ada2) and histone deacetylase (hos2, clr6) activities smooth or abolish the mat-bias. In addition, the mat-bias depends on the presence of Swi5. We propose a new role for Swi5 and the histone acetylation status in mat-bias establishment through directionality of repair from the intact chromatid to the broken chromatid.

Parvanov, Emil; Kohli, Juerg; Ludin, Katja

2008-01-01

51

Cloning and analysis of the mating-type idiomorphs from the barley pathogen Septoria passerinii  

Microsoft Academic Search

The genus Septoria contains more than 1000 species of plant pathogenic fungi, most of which have no known sexual stage. Species of Septoria without a known sexual stage could be recent derivatives of sexual species that have lost the ability to mate. To test this hypothesis, the mating-type region of S. passerinii, a species with no known sexual stage, was

S. B. Goodwin; C. Waalwijk; G. H. J. Kema; J. R. Cavaletto; G. Zhang

2003-01-01

52

Cloning and analysis of the mating-type idiomorphs from the barley pathogen Septoria passerinii.  

PubMed

The genus Septoria contains more than 1000 species of plant pathogenic fungi, most of which have no known sexual stage. Species of Septoria without a known sexual stage could be recent derivatives of sexual species that have lost the ability to mate. To test this hypothesis, the mating-type region of S. passerinii, a species with no known sexual stage, was cloned, sequenced, and compared to that of its close relative S. tritici (sexual stage: Mycosphaerella graminicola). Both of the S. passerinii mating-type idiomorphs were approximately 3 kb in size and contained a single reading frame interrupted by one (MAT-2) or two (MAT-1) putative introns. The putative products of MAT-1 and MAT-2 are characterized by alpha-box and high-mobility-group sequences, respectively, similar to those in the mating-type genes of M. graminicolaand other fungi. The mating-type genes of S. passerinii and M. graminicolaare evolving rapidly, approximately ten times faster than the internal transcribed spacer region of the ribosomal DNA, and are not closely related to those from Cochliobolusor other loculoascomycetes in the order Pleosporales. Therefore, the class Loculoascomycetes may be polyphyletic. Furthermore, differences between the phylogenetic trees may indicate separate evolutionary histories for the MAT-1 and MAT-2 idiomorphs. A three-primer multiplex-PCR technique was developed that allowed rapid identification of the mating types of isolates of S. passerinii. Both mating types were present in approximately equal frequencies and often on the same leaf in fields in Minnesota and North Dakota. Analyses with isozyme and random amplified polymorphic DNA markers revealed that each isolate had a unique genotype. The common occurrence of both mating types on the same leaf and the high levels of genotypic diversity indicate that S. passerinii is almost certainly not an asexual derivative of a sexual fungus. Instead, sexual reproduction probably plays an integral role in the life cycle of S. passerinii and may be much more important than previously believed in this (and possibly other) "asexual" species of Septoria. PMID:12715148

Goodwin, S B; Waalwijk, C; Kema, G H J; Cavaletto, J R; Zhang, G

2003-04-01

53

Evolutionary Dynamics of Mating-Type Loci of Mycosphaerella spp. Occurring on Banana? †  

PubMed Central

The devastating Sigatoka disease complex of banana is primarily caused by three closely related heterothallic fungi belonging to the genus Mycosphaerella: M. fijiensis, M. musicola, and M. eumusae. Previous phylogenetic work showing common ancestry led us to analyze the mating-type loci of these Mycosphaerella species occurring on banana. We reasoned that this might provide better insight into the evolutionary history of these species. PCR and chromosome-walking approaches were used to clone the mating-type loci of M. musicola and M. eumusae. Sequences were compared to the published mating-type loci of M. fijiensis and other Mycosphaerella spp., and a novel organization of the MAT loci was found. The mating-type loci of the examined Mycosphaerella species are expanded, containing two additional Mycosphaerella-specific genes in a unique genomic organization. The proteins encoded by these novel genes show a higher interspecies than intraspecies homology. Moreover, M. fijiensis, M. musicola, and M. eumusae contain two additional mating-type-like loci, containing parts of both MAT1-1-1 and MAT1-2-1. The data indicate that M. fijiensis, M. musicola, and M. eumusae share an ancestor in which a fusion event occurred between MAT1-1-1 and MAT1-2-1 sequences and in which additional genes became incorporated into the idiomorph. The new genes incorporated have since then evolved independently in the MAT1-1 and MAT1-2 loci. Thus, these data are an example of the evolutionary dynamics of fungal MAT loci in general and show the great flexibility of the MAT loci of Mycosphaerella species in particular.

Arzanlou, Mahdi; Crous, Pedro W.; Zwiers, Lute-Harm

2010-01-01

54

Evolutionary dynamics of mating-type loci of Mycosphaerella spp. occurring on banana.  

PubMed

The devastating Sigatoka disease complex of banana is primarily caused by three closely related heterothallic fungi belonging to the genus Mycosphaerella: M. fijiensis, M. musicola, and M. eumusae. Previous phylogenetic work showing common ancestry led us to analyze the mating-type loci of these Mycosphaerella species occurring on banana. We reasoned that this might provide better insight into the evolutionary history of these species. PCR and chromosome-walking approaches were used to clone the mating-type loci of M. musicola and M. eumusae. Sequences were compared to the published mating-type loci of M. fijiensis and other Mycosphaerella spp., and a novel organization of the MAT loci was found. The mating-type loci of the examined Mycosphaerella species are expanded, containing two additional Mycosphaerella-specific genes in a unique genomic organization. The proteins encoded by these novel genes show a higher interspecies than intraspecies homology. Moreover, M. fijiensis, M. musicola, and M. eumusae contain two additional mating-type-like loci, containing parts of both MAT1-1-1 and MAT1-2-1. The data indicate that M. fijiensis, M. musicola, and M. eumusae share an ancestor in which a fusion event occurred between MAT1-1-1 and MAT1-2-1 sequences and in which additional genes became incorporated into the idiomorph. The new genes incorporated have since then evolved independently in the MAT1-1 and MAT1-2 loci. Thus, these data are an example of the evolutionary dynamics of fungal MAT loci in general and show the great flexibility of the MAT loci of Mycosphaerella species in particular. PMID:19915079

Arzanlou, Mahdi; Crous, Pedro W; Zwiers, Lute-Harm

2010-01-01

55

A Multiplex PCR Test for Determination of Mating Type Applied to the Plant Pathogens Tapesia yallundae and Tapesia acuformis  

Microsoft Academic Search

A multiplex PCR test for determining mating type of the pathogens Tapesia yallundae and Tapesia acuformis is described. The test involves three primers: a “common” primer annealing to DNA sequence conserved in the flanking region of both mating-type idiomorphs and two specific primers annealing to sequence in either the MAT-1 or the MAT-2 idiomorphs. Locating the specific primers in different

P. S. Dyer; P. A. Furneaux; G. Douhan; T. D. Murray

2001-01-01

56

Sex-Determination System in the Diploid Yeast Zygosaccharomyces sapae  

PubMed Central

Sexual reproduction and breeding systems are driving forces for genetic diversity. The mating-type (MAT) locus represents a mutation and chromosome rearrangement hotspot in yeasts. Zygosaccharomyces rouxii complex yeasts are naturally faced with hostile low water activity (aw) environments and are characterized by gene copy number variation, genome instability, and aneuploidy/allodiploidy. Here, we investigated sex-determination system in Zygosaccharomyces sapae diploid strain ABT301T, a member of the Z. rouxii complex. We cloned three divergent mating type-like (MTL) ?-idiomorph sequences and designated them as ZsMTL? copies 1, 2, and 3. They encode homologs of Z. rouxii CBS 732T MAT?2 (amino acid sequence identities spanning from 67.0 to 99.5%) and MAT?1 (identity range 81.5–99.5%). ABT301T possesses two divergent HO genes encoding distinct endonucleases 100% and 92.3% identical to Z. rouxii HO. Cloning of MATa-idiomorph resulted in a single ZsMTLa locus encoding two Z. rouxii-like proteins MATa1 and MATa2. To assign the cloned ZsMTL? and ZsMTLa idiomorphs as MAT, HML, and HMR cassettes, we analyzed their flanking regions. Three ZsMTL? loci exhibited the DIC1-MAT-SLA2 gene order canonical for MAT expression loci. Furthermore, four putative HML cassettes were identified, two containing the ZsMTL? copy 1 and the remaining harboring ZsMTL? copies 2 and 3. Finally, the ZsMTLa locus was 3?-flanked by SLA2, suggesting the status of MAT expression locus. In conclusion, Z. sapae ABT301T displays an a??? genotype missing of the HMR silent cassette. Our results demonstrated that mating-type switching is a hypermutagenic process in Z. rouxii complex that generates genetic diversity de novo. This error-prone mechanism could be suitable to generate progenies more rapidly adaptable to hostile environments.

Solieri, Lisa; Dakal, Tikam Chand; Giudici, Paolo; Cassanelli, Stefano

2014-01-01

57

Sex-Determination System in the Diploid Yeast Zygosaccharomyces sapae.  

PubMed

Sexual reproduction and breeding systems are driving forces for genetic diversity. The mating-type (MAT) locus represents a mutation and chromosome rearrangement hotspot in yeasts. Zygosaccharomyces rouxii complex yeasts are naturally faced with hostile low water activity (aw) environments and are characterized by gene copy number variation, genome instability, and aneuploidy/allodiploidy. Here, we investigated sex-determination system in Zygosaccharomyces sapae diploid strain ABT301(T), a member of the Z. rouxii complex. We cloned three divergent mating type-like (MTL) ?-idiomorph sequences and designated them as ZsMTL? copies 1, 2, and 3. They encode homologs of Z. rouxii CBS 732(T) MAT?2 (amino acid sequence identities spanning from 67.0 to 99.5%) and MAT?1 (identity range 81.5-99.5%). ABT301(T) possesses two divergent HO genes encoding distinct endonucleases 100% and 92.3% identical to Z. rouxii HO. Cloning of MATA: -idiomorph resulted in a single ZsMTLA: locus encoding two Z. rouxii-like proteins MATA: 1 and MATA: 2. To assign the cloned ZsMTL? and ZsMTLA: idiomorphs as MAT, HML, and HMR cassettes, we analyzed their flanking regions. Three ZsMTL? loci exhibited the DIC1-MAT-SLA2 gene order canonical for MAT expression loci. Furthermore, four putative HML cassettes were identified, two containing the ZsMTL? copy 1 and the remaining harboring ZsMTL? copies 2 and 3. Finally, the ZsMTLA: locus was 3'-flanked by SLA2, suggesting the status of MAT expression locus. In conclusion, Z. sapae ABT301(T) displays an a??? genotype missing of the HMR silent cassette. Our results demonstrated that mating-type switching is a hypermutagenic process in Z. rouxii complex that generates genetic diversity de novo. This error-prone mechanism could be suitable to generate progenies more rapidly adaptable to hostile environments. PMID:24939186

Solieri, Lisa; Dakal, Tikam Chand; Giudici, Paolo; Cassanelli, Stefano

2014-01-01

58

Defining the epigenetic mechanism of asymmetric cell division of Schizosaccharomyces japonicus yeast.  

PubMed

A key question in developmental biology addresses the mechanism of asymmetric cell division. Asymmetry is crucial for generating cellular diversity required for development in multicellular organisms. As one of the potential mechanisms, chromosomally borne epigenetic difference between sister cells that changes mating/cell type has been demonstrated only in the Schizosaccharomyces pombe fission yeast. For technical reasons, it is nearly impossible to determine the existence of such a mechanism operating during embryonic development of multicellular organisms. Our work addresses whether such an epigenetic mechanism causes asymmetric cell division in the recently sequenced fission yeast, S. japonicus (with 36% GC content), which is highly diverged from the well-studied S. pombe species (with 44% GC content). We find that the genomic location and DNA sequences of the mating-type loci of S. japonicus differ vastly from those of the S. pombe species. Remarkably however, similar to S. pombe, the S. japonicus cells switch cell/mating type after undergoing two consecutive cycles of asymmetric cell divisions: only one among four "granddaughter" cells switches. The DNA-strand-specific epigenetic imprint at the mating-type locus1 initiates the recombination event, which is required for cellular differentiation. Therefore the S. pombe and S. japonicus mating systems provide the first two examples in which the intrinsic chirality of double helical structure of DNA forms the primary determinant of asymmetric cell division. Our results show that this unique strand-specific imprinting/segregation epigenetic mechanism for asymmetric cell division is evolutionary conserved. Motivated by these findings, we speculate that DNA-strand-specific epigenetic mechanisms might have evolved to dictate asymmetric cell division in diploid, higher eukaryotes as well. PMID:23150598

Yu, Chuanhe; Bonaduce, Michael J; Klar, Amar J S

2013-01-01

59

Mating-type genes for basidiomycete strain improvement in mushroom farming  

Microsoft Academic Search

Mushroom production is dependent on the quality of the spawn used to inoculate the cultures. In order to produce high-quality spawn, breeding programs for strains resistant to certain diseases and able to form high-quality fruit bodies under standard growth conditions are necessary. The investigation of the molecular basis for mating provides access to the use of mating-type genes in order

E. Kothe

2001-01-01

60

Cloning and analysis of the mating type genes from Cochliobolus heterostrophus  

Microsoft Academic Search

Cochliobolus heterostrophus, a heterothallic Ascomycete, has a single mating type locus with two alternate forms called MAT-1 and MAT-2. MAT-1 was cloned by complementing a MAT-2 strain using a cosmid library from a MAT-1 strain and screening for a homothallic transformant. The cosmid recovered from this transformant was able to re-transform a MAT-2 strain to homothallism and MAT identity was

B. Gillian Turgeon; Holger Bohlmann; Lynda M. Ciuffetti; Solveig K. Christiansen; Ge Yang; Willi Schfifer; O. C. Yoder

1993-01-01

61

Genome-defence small RNAs exapted for epigenetic mating-type inheritance.  

PubMed

In the ciliate Paramecium, transposable elements and their single-copy remnants are deleted during the development of somatic macronuclei from germline micronuclei, at each sexual generation. Deletions are targeted by scnRNAs, small RNAs produced from the germ line during meiosis that first scan the maternal macronuclear genome to identify missing sequences, and then allow the zygotic macronucleus to reproduce the same deletions. Here we show that this process accounts for the maternal inheritance of mating types in Paramecium tetraurelia, a long-standing problem in epigenetics. Mating type E depends on expression of the transmembrane protein mtA, and the default type O is determined during development by scnRNA-dependent excision of the mtA promoter. In the sibling species Paramecium septaurelia, mating type O is determined by coding-sequence deletions in a different gene, mtB, which is specifically required for mtA expression. These independently evolved mechanisms suggest frequent exaptation of the scnRNA pathway to regulate cellular genes and mediate transgenerational epigenetic inheritance of essential phenotypic polymorphisms. PMID:24805235

Singh, Deepankar Pratap; Saudemont, Baptiste; Guglielmi, Gérard; Arnaiz, Olivier; Goût, Jean-François; Prajer, Malgorzata; Potekhin, Alexey; Przybòs, Ewa; Aubusson-Fleury, Anne; Bhullar, Simran; Bouhouche, Khaled; Lhuillier-Akakpo, Maoussi; Tanty, Véronique; Blugeon, Corinne; Alberti, Adriana; Labadie, Karine; Aury, Jean-Marc; Sperling, Linda; Duharcourt, Sandra; Meyer, Eric

2014-05-22

62

Virulence in an insect model differs between mating types in Aspergillus fumigatus.  

PubMed

Aspergillus fumigatus is an opportunistic fungal pathogen that has recently been found to undergo sexual reproduction. Previous work suggested that invasiveness differs between mating types, and in the present study we tested whether virulence differs between mating types in an in vivo model, i.e., larvae of the wax moth Galleria mellonella. We measured virulence of 20 A. fumigatus isolates; three MAT1-1 isolates of environmental origin, five MAT1-1 isolates of clinical origin, seven MAT1-2 isolates of environmental origin and five MAT1-2 isolates of clinical origin. For each isolate, we measured virulence in six replicates and for each replicate, conidia were grown, harvested, and counted independently, and 2,500 colony forming units were injected into each of 10 G. mellonella larvae. Virulence differed between mating types, with lower survival in larvae injected with MAT1-1 isolates. Virulence also differed between clinical and environmental isolates, but surprisingly larvae injected with environmental isolates had lower survival. Identification of the mechanisms underlying variation in virulence may identify novel targets for the treatment of Aspergillus infections. PMID:20818921

Cheema, Manjinder S; Christians, Julian K

2011-02-01

63

Cooperative biosynthesis of Trisporoids by the (+) and (-) mating types of the zygomycete Blakeslea trispora.  

PubMed

The fungal phylum zygomycota uses trisporic acids (TSAs), a family of apocarotenoids, during sexual reproduction to synchronize and control activity between the mycelial hyphae of opposite mating types. Separate as well as mixed cultures of Blakeslea trispora were systematically supplemented with putative, deuterium-labeled precursors downstream of beta-carotene en route to the bioactive TSAs. Analysis of the isolated metabolites allowed the reconstruction of the complete biosynthetic sequence between the first apocarotenoid, D'orenone (1), and the different series of TSAs B (8) and C (13). Both mating types produced a similar spectrum of early metabolites upstream of trisporols B (7) and C (12), while only the (+) type was able to further oxidize trisporols B (7) and C (12) to the corresponding methyltrisporoid B (5) and C (11), respectively. A novel 4-dihydrotrisporic acid B (14) that was not formed from the labeled precursors was isolated from mated strains; this compound might be derived from oxygenated beta-carotene by a parallel pathway. The ester accumulated in the culture broth of the (+) strain and was only hydrolyzed by mycelia of the (-) strain; this corresponds to a synchronization of the biosynthetic activities of both mating types. PMID:19035372

Schachtschabel, Doreen; David, Anja; Menzel, Klaus-Dieter; Schimek, Christine; Wöstemeyer, Johannes; Boland, Wilhelm

2008-12-15

64

The cAMP pathway is important for controlling the morphological switch to the pathogenic yeast form of Paracoccidioides brasiliensis  

PubMed Central

Paracoccidioides brasiliensis is a human pathogenic fungus that switches from a saprobic mycelium to a pathogenic yeast. Consistent with the morphological transition being regulated by the cAMP-signalling pathway, there is an increase in cellular cAMP levels both transiently at the onset (< 24 h) and progressively in the later stages (> 120 h) of the transition to the yeast form, and this transition can be modulated by exogenous cAMP. We have cloned the cyr1 gene encoding adenylate cyclase (AC) and established that its transcript levels correlate with cAMP levels. In addition, we have cloned the genes encoding three G? (Gpa1–3), G? (Gpb1) and G? (Gpg1) G proteins. Gpa1 and Gpb1 interact with one another and the N-terminus of AC, but neither Gpa2 nor Gpa3 interacted with Gpb1 or AC. The interaction of Gpa1 with Gpb1 was blocked by GTP, but its interaction with AC was independent of bound nucleotide. The transcript levels for gpa1, gpb1 and gpg1 were similar in mycelium, but there was a transient excess of gpb1 during the transition, and an excess of gpa1 in yeast. We have interpreted our findings in terms of a novel signalling mechanism in which the activity of AC is differentially modulated by Gpa1 and Gpb1 to maintain the signal over the 10 days needed for the morphological switch.

Chen, Daliang; Janganan, Thamarai K; Chen, Gongyou; Marques, Everaldo R; Kress, Marcia R; Goldman, Gustavo H; Walmsley, Adrian R; Borges-Walmsley, M Ines

2007-01-01

65

Mating-type genes and the genetic structure of a world-wide collection of the tomato pathogen Cladosporium fulvum.  

PubMed

Two mating-type genes, designated MAT1-1-1 and MAT1-2-1, were cloned and sequenced from the presumed asexual ascomycete Cladosporium fulvum (syn. Passalora fulva). The encoded products are highly homologous to mating-type proteins from members of the Mycosphaerellaceae, such as Mycosphaerella graminicola and Cercospora beticola. In addition, the two MAT idiomorphs of C. fulvum showed regions of homology and each contained one additional putative ORF without significant similarity to known sequences. The distribution of the two mating-type genes in a world-wide collection of 86 C. fulvum strains showed a departure from a 1:1 ratio (chi(2)=4.81, df=1). AFLP analysis revealed a high level of genotypic diversity, while strains of the fungus were identified with similar virulence spectra but distinct AFLP patterns and opposite mating-types. These features could suggest the occurrence of recombination in C. fulvum. PMID:17178244

Stergiopoulos, Ioannis; Groenewald, Marizeth; Staats, Martijn; Lindhout, Pim; Crous, Pedro W; De Wit, Pierre J G M

2007-05-01

66

Presence and functionality of mating type genes in the supposedly asexual filamentous fungus Aspergillus oryzae.  

PubMed

The potential for sexual reproduction in Aspergillus oryzae was assessed by investigating the presence and functionality of MAT genes. Previous genome studies had identified a MAT1-1 gene in the reference strain RIB40. We now report the existence of a complementary MAT1-2 gene and the sequencing of an idiomorphic region from A. oryzae strain AO6. This allowed the development of a PCR diagnostic assay, which detected isolates of the MAT1-1 and MAT1-2 genotypes among 180 strains assayed, including industrial tane-koji isolates. Strains used for sake and miso production showed a near-1:1 ratio of the MAT1-1 and MAT1-2 mating types, whereas strains used for soy sauce production showed a significant bias toward the MAT1-2 mating type. MAT1-1 and MAT1-2 isogenic strains were then created by genetic manipulation of the resident idiomorph, and gene expression was compared by DNA microarray and quantitative real-time PCR (qRT-PCR) methodologies under conditions in which MAT genes were expressed. Thirty-three genes were found to be upregulated more than 10-fold in either the MAT1-1 host strain or the MAT1-2 gene replacement strain relative to each other, showing that both the MAT1-1 and MAT1-2 genes functionally regulate gene expression in A. oryzae in a mating type-dependent manner, the first such report for a supposedly asexual fungus. MAT1-1 expression specifically upregulated an ?-pheromone precursor gene, but the functions of most of the genes affected were unknown. The results are consistent with a heterothallic breeding system in A. oryzae, and prospects for the discovery of a sexual cycle are discussed. PMID:22327593

Wada, Ryuta; Maruyama, Jun-Ichi; Yamaguchi, Haruka; Yamamoto, Nanase; Wagu, Yutaka; Paoletti, Mathieu; Archer, David B; Dyer, Paul S; Kitamoto, Katsuhiko

2012-04-01

67

Multiple regulation of STE2, a mating-type-specific gene of Saccharomyces cerevisiae.  

PubMed Central

The Saccharomyces cerevisiae STE2 gene, which is required for pheromone response and conjugation specifically in mating-type a cells, was cloned by complementation of the ste2 mutation. Transcription of STE2 is repressed by the MAT alpha 2 gene product, so that the 1.4-kilobase STE2 RNA is detected only in a or mat alpha 2 strains, not in alpha or a/alpha cells. However, STE2 RNA levels are also increased by the mating pheromone alpha-factor and decreased in strains bearing mutations in the nonspecific STE4 gene. Regulation of STE2 expression in a cells is therefore achieved by several mechanisms. Images

Hartig, A; Holly, J; Saari, G; MacKay, V L

1986-01-01

68

Characterization of Phytophthora infestans populations in Colombia: first report of the A2 mating type.  

PubMed

Phytophthora infestans, the causal agent of late blight in crops of the Solanaceae family, is one of the most important plant pathogens in Colombia. Not only are Solanum lycopersicum, and S. tuberosum at risk, but also several other solanaceous hosts (Physalis peruviana, S. betaceum, S. phureja, and S. quitoense) that have recently gained importance as new crops in Colombia may be at risk. Because little is known about the population structure of Phytophthora infestans in Colombia, we report here the phenotypic and molecular characterization of 97 isolates collected from these six different solanaceous plants in Colombia. All the isolates were analyzed for mating type, mitochondrial haplotypes, genotype for several microsatellites, and sequence of the internal transcribed spacer (ITS) region. This characterization identified a single individual of A2 mating type (from Physalis peruviana) for the first time in Colombia. All isolates had an ITS sequence that was at least 97% identical to the consensus sequence. Of the 97 isolates, 96 were mitochondrial haplotype IIa, with the single A2 isolate being Ia. All isolates were invariant for the microsatellites. Additionally, isolates collected from S. tuberosum and P. peruviana (64 isolates) were tested for: aggressiveness on both hosts, genotype for the isozymes (glucose-6-phosphate isomerase and peptidase), and restriction fragment length polymorphism fingerprint pattern as detected by RG57. Isolates from S. tuberosum were preferentially pathogenic on S. tuberosum, and isolates from P. peruviana were preferentially pathogenic on P. peruviana. The population from these two hosts was dominated by a single clonal lineage (59 of 64 individuals assayed), previously identified from Ecuador and Peru as EC-1. This lineage was mating type A1, IIa for mitochondrial DNA, invariant for two microsatellites, and invariant for both isozymes. The remaining four A1 isolates were in lineages very closely related to EC-1 (named EC-1.1, CO-1, and CO-2). The remaining lineage (the A2 mating type) had characteristics of the US-8 lineage (previously identified in Mexico, the United States, and Canada). These results have important epidemiological implications for the production of these two crops in Colombia. PMID:19055438

Vargas, Angela M; Quesada Ocampo, Lina M; Céspedes, Maria Catalina; Carreño, Natalia; González, Adriana; Rojas, Alejandro; Zuluaga, A Paola; Myers, Kevin; Fry, William E; Jiménez, Pedro; Bernal, Adriana J; Restrepo, Silvia

2009-01-01

69

Homology modeling and mutational analysis of Ho endonuclease of yeast.  

PubMed Central

Ho endonuclease is a LAGLIDADG homing endonuclease that initiates mating-type interconversion in yeast. Ho is encoded by a free-standing gene but shows 50% primary sequence similarity to the intein (protein-intron encoded) PI-SceI. Ho is unique among LAGLIDADG endonucleases in having a 120-residue C-terminal putative zinc finger domain. The crystal structure of PI-SceI revealed a bipartite enzyme with a protein-splicing domain (Hint) and intervening endonuclease domain. We made a homology model for Ho on the basis of the PI-SceI structure and performed mutational analysis of putative critical residues, using a mating-type switch as a bioassay for activity and GFP-fusion proteins to detect nuclear localization. We found that residues of the N-terminal sequence of the Hint domain are important for Ho activity, in particular the DNA recognition region. C-terminal residues of the Hint domain are dispensable for Ho activity; however, the C-terminal putative zinc finger domain is essential. Mutational analysis indicated that residues in Ho that are conserved relative to catalytic, active-site residues in PI-SceI and other related homing endonucleases are essential for Ho activity. Our results indicate that in addition to the conserved catalytic residues, Hint domain residues and the zinc finger domain have evolved a critical role in Ho activity.

Bakhrat, Anya; Jurica, Melissa S; Stoddard, Barry L; Raveh, Dina

2004-01-01

70

Genetic variability and distribution of mating type alleles in field populations of Leptosphaeria maculans from France.  

PubMed

Leptosphaeria maculans is the most ubiquitous fungal pathogen of Brassica crops and causes the devastating stem canker disease of oilseed rape worldwide. We used minisatellite markers to determine the genetic structure of L. maculans in four field populations from France. Isolates were collected at three different spatial scales (leaf, 2-m2 field plot, and field) enabling the evaluation of spatial distribution of the mating type alleles and of genetic variability within and among field populations. Within each field population, no gametic disequilibrium between the minisatellite loci was detected and the mating type alleles were present at equal frequencies. Both sexual and asexual reproduction occur in the field, but the genetic structure of these populations is consistent with annual cycles of randomly mating sexual reproduction. All L. maculans field populations had a high level of gene diversity (H = 0.68 to 0.75) and genotypic diversity. Within each field population, the number of genotypes often was very close to the number of isolates. Analysis of molecular variance indicated that >99.5% of the total genetic variability was distributed at a small spatial scale, i.e., within 2-m2 field plots. Population differentiation among the four field populations was low (GST < 0.02), suggesting a high degree of gene exchange between these populations. The high gene flow evidenced here in French populations of L. maculans suggests a rapid countrywide diffusion of novel virulence alleles whenever novel resistance sources are used. PMID:16391041

Gout, Lilian; Eckert, Maria; Rouxel, Thierry; Balesdent, Marie-Hélène

2006-01-01

71

Organization and evolutionary trajectory of the mating type (MAT) locus in dermatophyte and dimorphic fungal pathogens.  

PubMed

Sexual reproduction in fungi is governed by a specialized genomic region, the mating type (MAT) locus, whose gene identity, organization, and complexity are diverse. We identified the MAT locus of five dermatophyte fungal pathogens (Microsporum gypseum, Microsporum canis, Trichophyton equinum, Trichophyton rubrum, and Trichophyton tonsurans) and a dimorphic fungus, Paracoccidioides brasiliensis, and performed phylogenetic analyses. The identified MAT locus idiomorphs of M. gypseum control cell type identity in mating assays, and recombinant progeny were produced. Virulence tests in Galleria mellonella larvae suggest the two mating types of M. gypseum may have equivalent virulence. Synteny analysis revealed common features of the MAT locus shared among these five dermatophytes: namely, a small size ( approximately 3 kb) and a novel gene arrangement. The SLA2, COX13, and APN2 genes, which flank the MAT locus in other Ascomycota are instead linked on one side of the dermatophyte MAT locus. In addition, the transcriptional orientations of the APN2 and COX13 genes are reversed compared to the dimorphic fungi Histoplasma capsulatum, Coccidioides immitis, and Coccidioides posadasii. A putative transposable element, pogo, was found to have inserted in the MAT1-2 idiomorph of one P. brasiliensis strain but not others. In conclusion, the evolution of the MAT locus of the dermatophytes and dimorphic fungi from the last common ancestor has been punctuated by both gene acquisition and expansion, and asymmetric gene loss. These studies further support a foundation to develop molecular and genetic tools for dermatophyte and dimorphic human fungal pathogens. PMID:19880755

Li, Wenjun; Metin, Banu; White, Theodore C; Heitman, Joseph

2010-01-01

72

Organization and Evolutionary Trajectory of the Mating Type (MAT) Locus in Dermatophyte and Dimorphic Fungal Pathogens? †  

PubMed Central

Sexual reproduction in fungi is governed by a specialized genomic region, the mating type (MAT) locus, whose gene identity, organization, and complexity are diverse. We identified the MAT locus of five dermatophyte fungal pathogens (Microsporum gypseum, Microsporum canis, Trichophyton equinum, Trichophyton rubrum, and Trichophyton tonsurans) and a dimorphic fungus, Paracoccidioides brasiliensis, and performed phylogenetic analyses. The identified MAT locus idiomorphs of M. gypseum control cell type identity in mating assays, and recombinant progeny were produced. Virulence tests in Galleria mellonella larvae suggest the two mating types of M. gypseum may have equivalent virulence. Synteny analysis revealed common features of the MAT locus shared among these five dermatophytes: namely, a small size (?3 kb) and a novel gene arrangement. The SLA2, COX13, and APN2 genes, which flank the MAT locus in other Ascomycota are instead linked on one side of the dermatophyte MAT locus. In addition, the transcriptional orientations of the APN2 and COX13 genes are reversed compared to the dimorphic fungi Histoplasma capsulatum, Coccidioides immitis, and Coccidioides posadasii. A putative transposable element, pogo, was found to have inserted in the MAT1-2 idiomorph of one P. brasiliensis strain but not others. In conclusion, the evolution of the MAT locus of the dermatophytes and dimorphic fungi from the last common ancestor has been punctuated by both gene acquisition and expansion, and asymmetric gene loss. These studies further support a foundation to develop molecular and genetic tools for dermatophyte and dimorphic human fungal pathogens.

Li, Wenjun; Metin, Banu; White, Theodore C.; Heitman, Joseph

2010-01-01

73

Isolation of Neurospora Crassa a Mating Type Mutants by Repeat Induced Point (Rip) Mutation  

PubMed Central

In the filamentous fungus, Neurospora crassa, mating type is regulated by a single locus with alternate alleles, termed A and a. The mating type alleles control entry into the sexual cycle, but during vegetative growth they function to elicit heterokaryon incompatibility, such that fusion of A and a hypha results in death of cells along the fusion point. Previous studies have shown that the A allele consists of 5301 bp and has no similarity to the a allele; it is found as a single copy and only within the A genome. The a allele is 3235 bp in length and it, too, is found as a single copy within the a genome. Within the A sequence, a single open reading frame (ORF) of 288 amino acids (mt A-1) is thought to confer fertility and heterokaryon incompatibility. In this study, we have used repeat induced point (RIP) mutation to identify functional regions of the A idiomorph. RIP mutations in mt A-1 resulted in the isolation of sterile, heterokaryon-compatible mutants, while RIP mutations generated in a region outside of mt A-1 resulted in the isolation of mutants capable of mating, but deficient in ascospore formation.

Glass, N. L.; Lee, L.

1992-01-01

74

Scanning electron microscopy as a tool for the analysis of colony architecture produced by phenotypic switching of a human pathogenic yeast Candida tropicalis  

NASA Astrophysics Data System (ADS)

Candida tropicalis has been identified as one of the most prevalent pathogenic yeast species of the Candida-non-albicans group. Phenotypic switching is a biological phenomenon related to the occurrence of spontaneous emergence of colonies with different morphologies that provides variability within colonizing populations in order to adapt to different environments. Currently, studies of the microstructure of switching variant colonies are not subject of extensive research. SEM analysis was used to verify the architecture of whole Candida colonies. The strain 49/07 exhibited a hemispherical shape character, while the strain 335/07 showed a volcano shape with mycelated-edge colony. The ring switch variant is characterized by a highly wrinkled centre and an irregular periphery. The rough phenotype exhibited a three-dimensional architecture and was characterized by the presence of deep central and peripheral depressions areas. The ultrastructural analysis also allowed the observation of the arrangement of individual cells within the colonies. The whole smooth colony consisted entirely of yeast cells. Differently, aerial filaments were found all around the colony periphery of the volcano shape colony. For this colony type the mycelated-edge consisted mainly of hyphae, although yeast cells are also seen. The ring and rough colonies phenotypes comprised mainly yeast cells with the presence of extracellular material connecting neighbouring cells. This study has shown that SEM can be used effectively to examine the microarchitecture of colonies morphotypes of the yeast C. tropicalis and further our understanding of switching event in this pathogen.

Furlaneto, M. C.; Andrade, C. G. T. J.; Aragão, P. H. A.; França, E. J. G.; Moralez, A. T. P.; Ferreira, L. C. S.

2012-07-01

75

Further evidence for sexual reproduction in Rhynchosporium secalis based on distribution and frequency of mating-type alleles.  

PubMed

Rhynchosporium secalis, the causal agent of scald on barley, is thought to be exclusively asexual because no teleomorph has been found. Partial sequences of the HMG-box and alpha-domain of Rhynchosporium secalis isolates were identified and used to develop a PCR assay for the mating-type locus. PCR amplification of only one of these two domains was possible in each strain, suggesting that R. secalis has a MAT organization that is similar to other known heterothallic fungi. A multiplex PCR with primers amplifying either a MAT1-1- or MAT1-2-specific amplicon was used to determine the distribution of mating types in several R. secalis populations. In total, 1101 isolates from Australia, Switzerland, Ethiopia, Scandinavia, California, and South Africa were included in the analysis. Mating types occurred in equal frequencies for most of these populations, suggesting frequency-dependent selection consistent with sexual reproduction. In addition, both mating types were frequently found occupying the same lesion or leaf, providing opportunities for isolates of opposite mating type to interact and reproduce sexually. We propose that R. secalis should be considered a sexual pathogen, although the sexual cycle may occur infrequently in some populations. PMID:14516764

Linde, Celeste C; Zala, Marcello; Ceccarelli, Sara; McDonald, Bruce A

2003-11-01

76

Characterization of dip1p reveals a switch in Arp2/3-dependent actin assembly for fission yeast endocytosis  

PubMed Central

Summary Background During endocytosis in yeast, a choreographed series of discrete local events at the plasma membrane lead to a rapid burst of actin polymerization and then internalization of an endocytic vesicle. What initiates Arp2/3-dependent actin polymerization in this process is not well understood. Results The Schizosaccharomyces pombe WISH/DIP/SPIN90 orthologue dip1p is an actin patch protein that regulates the temporal sequence of endocytic events. dip1? mutants exhibit a novel phenotype in which early events such as WASp localization occur normally, but arrival of Arp2/3, actin polymerization and subsequent steps are delayed and occur with apparently random timing. In studying this mutant, we demonstrate that positive feedback loops of WASp, rapid actin assembly, and Arp2/3 contribute to switch-like behavior that initiates actin polymerization. In the absence of dip1p, a subset of patches is activated concurrently with the “touch” of a neighboring endocytic vesicle. Conclusions These studies reveal a switch-like mechanism responsible for the initiation of actin assembly during endocytosis. This switch may be activated in at least two ways, through a dip1p-dependent mechanism and through contact with another endocytic vesicle.

Basu, Roshni; Chang, Fred

2011-01-01

77

Genetic diversity of the mating type and toxin production genes in Pyrenophora tritici-repentis.  

PubMed

Pyrenophora tritici-repentis, the causal agent of tan spot on wheat, is a homothallic loculoascomycete with a complex race structure. The objectives of this study were to confirm the homothallic nature of the pathogen, characterize mating type diversity and toxin production genes in a global collection of strains, and analyze how these traits are associated between each other and with existing races. The pseudothecia production capacity, race identification, mating type locus (MAT), internal transcribed spacer, and glyceraldehyde-3-phosphate dehydrogenase regions were analyzed in a selection of 88 strains originating from Europe, North and South America, North Africa, and Central and South Asia. Some (60%) strains produced pseudothecia containing ascospores, independent of their origin. Race identification obtained using the multiplex polymerase chain reaction targeting host-selective toxin (HST) genes was consistent, overall, with the results based on the inoculation of a set of differential wheat cultivars and confirmed the predominance of race 1/2 strains ( approximately 83%). However, discrepancies in race identification, differences from the reference tester strains, and atypical ToxA profiles suggest the presence of new races and HSTs. The MAT1-1 and MAT1-2 coding regions are consecutively arranged in a single individual, suggesting putative heterothallic origin of P. tritici-repentis. Upstream from the MAT is an open reading frame of unknown function (ORF1) containing a MAT-specific degenerate carboxy-terminus. The phylogenetic analysis of the MAT locus reveals two distinct groups, unlinked to geographical origin or ToxA profile. Group I, the best-represented group, is associated with typical tan spot lesions caused by races 1, 2, 3, and 5 on wheat. It is more homogenous than group II encompassing race 4 strains, as well as isolates associated primarily with small spot lesions on wheat leaves or other hosts. Group II could contain several distinct taxa. PMID:20373969

Lepoint, P; Renard, M-E; Legrève, A; Duveiller, E; Maraite, H

2010-05-01

78

Structure of a Ca2+-Myristoyl Switch Protein That Controls Activation of a Phosphatidylinositol 4-Kinase in Fission Yeast*  

PubMed Central

Neuronal calcium sensor (NCS) proteins transduce Ca2+ signals and are highly conserved from yeast to humans. We determined NMR structures of the NCS-1 homolog from fission yeast (Ncs1), which activates a phosphatidylinositol 4-kinase. Ncs1 contains an ?-NH2-linked myristoyl group on a long N-terminal arm and four EF-hand motifs, three of which bind Ca2+, assembled into a compact structure. In Ca2+-free Ncs1, the N-terminal arm positions the fatty acyl chain inside a cavity near the C terminus. The C14 end of the myristate is surrounded by residues in the protein core, whereas its amide-linked (C1) end is flanked by residues at the protein surface. In Ca2+-bound Ncs1, the myristoyl group is extruded (Ca2+-myristoyl switch), exposing a prominent patch of hydrophobic residues that specifically contact phosphatidylinositol 4-kinase. The location of the buried myristate and structure of Ca2+-free Ncs1 are quite different from those in other NCS proteins. Thus, a unique remodeling of each NCS protein by its myristoyl group, and Ca2+-dependent unmasking of different residues, may explain how each family member recognizes distinct target proteins.

Lim, Sunghyuk; Strahl, Thomas; Thorner, Jeremy; Ames, James B.

2011-01-01

79

Cloning of the Lentinula edodes B mating-type locus and identification of the genetic structure controlling B mating.  

PubMed

During the life cycle of heterothallic tetrapolar Agaricomycetes such as Lentinula edodes (Berk.) Pegler, the mating type system, composed of unlinked A and B loci, plays a vital role in controlling sexual development and resulting formation of the fruit body. L. edodes is produced worldwide for consumption and medicinal purposes, and understanding its sexual development is therefore of great importance. A considerable amount of mating type factors has been indicated over the past decades but few genes have actually been identified, and no complete genetic structures of L. edodes B mating-type loci are available. In this study, we cloned the matB regions from two mating compatible L. edodes strains, 939P26 and 939P42. Four pheromone receptors were identified on each new matB region, together with three and four pheromone precursor genes in the respective strains. Gene polymorphism, phylogenetic analysis and distribution of pheromone receptors and pheromone precursors clearly indicate a bipartite matB locus, each sublocus containing a pheromone receptor and one or two pheromone precursors. Detailed sequence comparisons of genetic structures between the matB regions of strains 939P42, 939P26 and a previously reported strain SUP2 further supported this model and allowed identification of the B mating type subloci borders. Mating studies confirmed the control of B mating by the identified pheromone receptors and pheromones in L. edodes. PMID:24029079

Wu, Lin; van Peer, Arend; Song, Wenhua; Wang, Hong; Chen, Mingjie; Tan, Qi; Song, Chunyan; Zhang, Meiyan; Bao, Dapeng

2013-12-01

80

DNA polymorphism in recombining and non-recombining mating-type-specific loci of the smut fungus Microbotryum.  

PubMed

The population-genetic processes leading to the genetic degeneration of non-recombining regions have mainly been studied in animal and plant sex chromosomes. Here, we report population genetic analysis of the processes in the non-recombining mating-type-specific regions of the smut fungus Microbotryum violaceum. M. violaceum has A1 and A2 mating types, determined by mating-type-specific 'sex chromosomes' that contain 1-2?Mb long non-recombining regions. If genetic degeneration were occurring, then one would expect reduced DNA polymorphism in the non-recombining regions of this fungus. The analysis of DNA diversity among 19 M. violaceum strains, collected across Europe from Silene latifolia flowers, revealed that (i) DNA polymorphism is relatively low in all 20 studied loci (??0.15%), (ii) it is not significantly different between the two mating-type-specific chromosomes nor between the non-recombining and recombining regions, (iii) there is substantial population structure in M. violaceum populations, which resembles that of its host species, S. latifolia, and (iv) there is significant linkage disequilibrium, suggesting that widespread selfing in this species results in a reduction of the effective recombination rate across the genome. We hypothesise that selfing-related reduction of recombination across the M. violaceum genome negates the difference in the level of DNA polymorphism between the recombining and non-recombining regions, and may possibly lead to similar levels of genetic degeneration in the mating-type-specific regions of the non-recombining 'sex chromosomes' and elsewhere in the genome. PMID:21081967

Votintseva, A A; Filatov, D A

2011-06-01

81

DNA polymorphism in recombining and non-recombing mating-type-specific loci of the smut fungus Microbotryum  

PubMed Central

The population-genetic processes leading to the genetic degeneration of non-recombining regions have mainly been studied in animal and plant sex chromosomes. Here, we report population genetic analysis of the processes in the non-recombining mating-type-specific regions of the smut fungus Microbotryum violaceum. M. violaceum has A1 and A2 mating types, determined by mating-type-specific ‘sex chromosomes' that contain 1–2?Mb long non-recombining regions. If genetic degeneration were occurring, then one would expect reduced DNA polymorphism in the non-recombining regions of this fungus. The analysis of DNA diversity among 19 M. violaceum strains, collected across Europe from Silene latifolia flowers, revealed that (i) DNA polymorphism is relatively low in all 20 studied loci (??0.15%), (ii) it is not significantly different between the two mating-type-specific chromosomes nor between the non-recombining and recombining regions, (iii) there is substantial population structure in M. violaceum populations, which resembles that of its host species, S. latifolia, and (iv) there is significant linkage disequilibrium, suggesting that widespread selfing in this species results in a reduction of the effective recombination rate across the genome. We hypothesise that selfing-related reduction of recombination across the M. violaceum genome negates the difference in the level of DNA polymorphism between the recombining and non-recombining regions, and may possibly lead to similar levels of genetic degeneration in the mating-type-specific regions of the non-recombining ‘sex chromosomes' and elsewhere in the genome.

Votintseva, A A; Filatov, D A

2011-01-01

82

Environmental and Genetic Determinants of Colony Morphology in Yeast  

PubMed Central

Nutrient stresses trigger a variety of developmental switches in the budding yeast Saccharomyces cerevisiae. One of the least understood of such responses is the development of complex colony morphology, characterized by intricate, organized, and strain-specific patterns of colony growth and architecture. The genetic bases of this phenotype and the key environmental signals involved in its induction have heretofore remained poorly understood. By surveying multiple strain backgrounds and a large number of growth conditions, we show that limitation for fermentable carbon sources coupled with a rich nitrogen source is the primary trigger for the colony morphology response in budding yeast. Using knockout mutants and transposon-mediated mutagenesis, we demonstrate that two key signaling networks regulating this response are the filamentous growth MAP kinase cascade and the Ras-cAMP-PKA pathway. We further show synergistic epistasis between Rim15, a kinase involved in integration of nutrient signals, and other genes in these pathways. Ploidy, mating-type, and genotype-by-environment interactions also appear to play a role in the controlling colony morphology. Our study highlights the high degree of network reuse in this model eukaryote; yeast use the same core signaling pathways in multiple contexts to integrate information about environmental and physiological states and generate diverse developmental outputs.

Granek, Joshua A.; Magwene, Paul M.

2010-01-01

83

Detection of resistance to fungicides, mating types and fitness of Phytophthora infestans in Hebei, China.  

PubMed

In vitro, isolates resistant to metalaxyl (M) and oxadixyl (O) of Phytophthora infestans were 11.2% of 62 isolates from potato and tomato in Hebei Province, mean resistance factor was 15,022 fold and 24,733 fold, respectively, no isolates resistant either to cymoxanil (C) or to dimethomorph (D) were detected. On the other hand, in vivo, isolates resistant to M and O were 29.0% and 32.7%, respectively, among 217 isolates from potato plants in Weichang and Chongli, Hebei, only one isolate resistant to M and O was found among 88 isolates from tomato plants in Xushui, Hebei. Among 73 isolates from potato in Weichang and Chongli, 6 isolates with A2 mating type were 8.2%, 3 A2 isolates resistant to metalaxyl and oxadixyl. 3 A2 isolates were 6.8% of 44 isolates from tomato in Xushui. Cross resistance in Phytophthora infestans was confirmed between M and O, but no cross resistance between C or D and M or O. The field isolates resistant to M and O were outstandingly fitter than sensitive or intermediate ones, mainly due to stronger sporulation capacity of the field isolates. PMID:12701437

Wang, Wen-Qiao; Ma, Zhi-Qiang; Han, Xiu-Ying; Zhang, Xiao-Feng; Chen, Shu-Long

2002-01-01

84

Evidence for interaction of Schizophyllum commune Y mating-type proteins in vivo.  

PubMed Central

The Aalpha mating-type locus of Schizophyllum commune regulates sexual development and contains the code for two proteins, Y and Z, which are thought to form a complex and function as a transcription factor. Import of these proteins into the nucleus may be an essential step in Aalpha-regulated sexual development. The Y proteins contain a bipartite basic sequence, which is an excellent candidate for a nuclear localization sequence (NLS), while Z proteins contain no such sequence. Here we describe experiments in which deletions were made in the putative NLS sequence of Y4. We show that this putative NLS is essential to the function of the Y protein and capable of mislocalizing green fluorescent protein (GFP) to the nucleus in Saccharomyces cerevisiae. Further, we describe genetic experiments that demonstrate the first Y-Y protein interactions in vivo. These results are consistent with our previously postulated hypothesis that the Y-Z complex is likely to be of a higher order than dimer.

Robertson, C Ian; McMahon Kende, Alexander; Toenjes, Kurt; Novotny, Charles P; Ullrich, Robert C

2002-01-01

85

Roles for internal and flanking sequences in regulating the activity of mating-type-silencer-associated replication origins in Saccharomyces cerevisiae.  

PubMed Central

ARS301 and ARS302 are inactive replication origins located at the left end of budding yeast (Saccharomyces cerevisiae) chromosome III, where they are associated with the HML-E and -I silencers of the HML mating type cassette. Although they function as replication origins in plasmids, they do not serve as origins in their normal chromosomal locations, because they are programmed to fire so late in S phase that they are passively replicated by the replication fork from neighboring early-firing ARS305 before they have a chance to fire on their own. We asked whether the nucleotide sequences required for plasmid origin function of these silencer-associated chromosomally inactive origins differ from the sequences needed for plasmid origin function by nonsilencer-associated chromosomally active origins. We could not detect consistent differences in sequence requirements for the two types of origins. Next, we asked whether sequences within or flanking these origins are responsible for their chromosomal inactivity. Our results demonstrate that both flanking and internal sequences contribute to chromosomal inactivity, presumably by programming these origins to fire late in S phase. In ARS301, the function of the internal sequences determining chromosomal inactivity is dependent on the checkpoint proteins Mec1p and Rad53p.

Sharma, K; Weinberger, M; Huberman, J A

2001-01-01

86

Distribution of mating types and genetic diversity induced by sexual recombination in Setosphaeria turcica in northern China  

Microsoft Academic Search

Mature ascocarps and ascospores in the heterothallic ascomycete fungus, Setosphaeria turcica, were successfully produced in Sach’s medium with barley culm as the mating stimulator after four weeks’ coincubation of\\u000a two opposite mating type isolates at 25°C in darkness. A single isolate could not produce ascospores or ascocarps. The ascocarps\\u000a were produced on the exposed surface and embedded parts of barley

Yongshan Fan; Jifang Ma; Xiumei Gui; Xinlong An; Shuqin Sun; Jingao Dong

2007-01-01

87

What is a bona fide mating-type gene? Internuclear complementation of mat mutants in Podospora anserina  

Microsoft Academic Search

In the heterothallic ascomycete Podospora anserina, the mating-type locus is occupied by two mutually exclusive sequences termed mat+ and mat–. The mat+ sequence contains only one gene, FPR1, while the mat– sequence contains three genes: FMR1, SMR1 and SMR2. Previous studies have demonstrated that FPR1 and FMR1 are required for fertilization. Further analyses have led to the hypothesis that mat+

S. Arnaise; R. Debuchy; M. Picard

1997-01-01

88

Identification of mating type loci and development of SCAR marker genetically linked to the B3 locus in Pleurotus eryngii.  

PubMed

In order to estimate how diverse the mating types in Pleurotus eryngii from different regions are, pairings between monokaryons derived from inter- and intragroups were done. Sixteen and 15 alleles were identified at loci A and B from the 12 strains. In the P. eryngii KNR2312, widely used for commercial production, four mating loci, A3, A4, B3, and B4, were determined. Those loci, except A3, were found in 4 strains out of 12 strains. To improve breeding efficiency, especially in mating type determination, RAPD and BSA were performed to screen for a mating type specific marker. The SCAR marker 13- 2(2100) was developed based on the RAPD-derived sequence typing B3 locus. The sequence analysis of 13-2(2100) revealed that it contained a conserved domain, the STE3 superfamily, and consensus sequences like the TATA box and GC box. It seems likely that the SCAR marker region is a part of the pheromone receptor gene. PMID:22814489

Ryu, Jae-San; Kim, Min Keun; Ro, Hyeon-Su; Kang, Young Min; Kwon, Jin-Hyeuk; Kong, Won-Sik; Lee, Hyun-Sook

2012-09-01

89

Repressive chromatin affects factor binding at yeast HO (homothallic switching) promoter.  

PubMed

The yeast HO gene is tightly regulated, with multiple activators and coactivators needed to overcome repressive chromatin structures that form over this promoter. Coactivator binding is strongly interdependent, as loss of one factor sharply reduces recruitment of other factors. The Rpd3(L) histone deacetylase is recruited to HO at two distinct times during the cell cycle, first by Ash1 to the URS1 region of the promoter and then by SBF/Whi5/Stb1 to URS2. SBF itself is localized to only a subset of its potential binding sites in URS2, and this localization takes longer and is less robust than at other SBF target genes, suggesting that binding to the HO promoter is limited by chromatin structures that dynamically change as the cell cycle progresses. Ash1 only binds at the URS1 region of the promoter, but an ash1 mutation results in markedly increased binding of SBF and Rpd3(L) at URS2, some 450 bp distant from the site of Ash1 binding, suggesting these two regions of the promoter interact. An ash1 mutation also results in increased coactivator recruitment, Swi/Snf and Mediator localization in the absence of the normally required Gcn5 histone acetyltransferase, and HO expression even in the presence of a taf1 mutation affecting TFIID activity that otherwise blocks HO transcription. Ash1 therefore appears to play a central role in generating the strongly repressive environment at the HO promoter, which limits the binding of several coactivators at URS2 and TATA region. PMID:21840992

Takahata, Shinya; Yu, Yaxin; Stillman, David J

2011-10-01

90

The Sclerotinia sclerotiorum Mating Type Locus (MAT) Contains a 3.6-kb Region That Is Inverted in Every Meiotic Generation  

PubMed Central

Sclerotinia sclerotiorum is a fungal plant pathogen and the causal agent of lettuce drop, an economically important disease of California lettuce. The structure of the S. sclerotiorum mating type locus MAT has previously been reported and consists of two idiomorphs that are fused end-to-end as in other homothallics. We investigated the diversity of S. sclerotiorum MAT using a total of 283 isolates from multiple hosts and locations, and identified a novel MAT allele that differed by a 3.6-kb inversion and was designated Inv+, as opposed to the previously known S. sclerotiorum MAT that lacked the inversion and was Inv-. The inversion affected three of the four MAT genes: MAT1-2-1 and MAT1-2-4 were inverted and MAT1-1-1 was truncated at the 3’-end. Expression of MAT genes differed between Inv+ and Inv- isolates. In Inv+ isolates, only one of the three MAT1-2-1 transcript variants of Inv- isolates was detected, and the alpha1 domain of Inv+ MAT1-1-1 transcripts was truncated. Both Inv- and Inv+ isolates were self-fertile, and the inversion segregated in a 1?1 ratio regardless of whether the parent was Inv- or Inv+. This suggested the involvement of a highly regulated process in maintaining equal proportions of Inv- and Inv+, likely associated with the sexual state. The MAT inversion region, defined as the 3.6-kb MAT inversion in Inv+ isolates and the homologous region of Inv- isolates, was flanked by a 250-bp inverted repeat on either side. The 250-bp inverted repeat was a partial MAT1-1-1 that through mediation of loop formation and crossing over, may be involved in the inversion process. Inv+ isolates were widespread, and in California and Nebraska constituted half of the isolates examined. We speculate that a similar inversion region may be involved in mating type switching in the filamentous ascomycetes Chromocrea spinulosa, Sclerotinia trifoliorum and in certain Ceratocystis species.

Maruthachalam, Karunakaran; Wu, Bo-Ming; Subbarao, Krishna V.

2013-01-01

91

Uneven Distribution of Mating Types among Genotypes of Candida glabrata Isolates from Clinical Samples  

Microsoft Academic Search

In order to shed light on its basic biology, we initiated a population genetic analysis of Candida glabrata ,a n emerging pathogenic yeast with no sexual stage yet recognized. A worldwide collection of clinical strains was subjected to analysis using variable number of tandem repeats (VNTR) at nine loci. The clustering of strains obtained with this method was congruent with

Sylvain Brisse; Christine Pannier; Adela Angoulvant; Thierry de Meeus; Laure Diancourt; Odile Faure; Heloïse Muller; Javier Peman; Maria Anna Viviani; Renee Grillot; Bernard Dujon; Cecile Fairhead; Christophe Hennequin

2009-01-01

92

Isolates of Cryptococcus neoformans from Infected Animals Reveal Genetic Exchange in Unisexual,   Mating Type Populations  

Microsoft Academic Search

Sexual reproduction and genetic exchange are important for the evolution of fungal pathogens and for producing potentially infective spores. Studies to determine whether sex occurs in the pathogenic yeast Cryptococcus neoformans var. grubii have produced enigmatic results, however: basidiospores are the most likely infective propagules, and clinical isolates are fertile and genetically diverse, consistent with a sexual species, but almost

Tien Bui; Xiaorong Lin; Richard Malik; Joseph Heitman; Dee Carter

2008-01-01

93

Functional Characterization of MAT1-1-Specific Mating-Type Genes in the Homothallic Ascomycete Sordaria macrospora Provides New Insights into Essential and Nonessential Sexual Regulators?†  

PubMed Central

Mating-type genes in fungi encode regulators of mating and sexual development. Heterothallic ascomycete species require different sets of mating-type genes to control nonself-recognition and mating of compatible partners of different mating types. Homothallic (self-fertile) species also carry mating-type genes in their genome that are essential for sexual development. To analyze the molecular basis of homothallism and the role of mating-type genes during fruiting-body development, we deleted each of the three genes, SmtA-1 (MAT1-1-1), SmtA-2 (MAT1-1-2), and SmtA-3 (MAT1-1-3), contained in the MAT1-1 part of the mating-type locus of the homothallic ascomycete species Sordaria macrospora. Phenotypic analysis of deletion mutants revealed that the PPF domain protein-encoding gene SmtA-2 is essential for sexual reproduction, whereas the ? domain protein-encoding genes SmtA-1 and SmtA-3 play no role in fruiting-body development. By means of cross-species microarray analysis using Neurospora crassa oligonucleotide microarrays hybridized with S. macrospora targets and quantitative real-time PCR, we identified genes expressed under the control of SmtA-1 and SmtA-2. Both genes are involved in the regulation of gene expression, including that of pheromone genes.

Klix, V.; Nowrousian, M.; Ringelberg, C.; Loros, J. J.; Dunlap, J. C.; Poggeler, S.

2010-01-01

94

Genetic Basis of Self-Incompatibility in the Lichen-Forming Fungus Lobaria pulmonaria and Skewed Frequency Distribution of Mating-Type Idiomorphs: Implications for Conservation  

PubMed Central

Fungal populations that reproduce sexually are likely to be genetically more diverse and have a higher adaptive potential than asexually reproducing populations. Mating systems of fungal species can be self-incompatible, requiring the presence of isolates of different mating-type genes for sexual reproduction to occur, or self-compatible, requiring only one. Understanding the distribution of mating-type genes in populations can help to assess the potential of self-incompatible species to reproduce sexually. In the locally threatened epiphytic lichen-forming fungus Lobaria pulmonaria (L.) Hoffm., low frequency of sexual reproduction is likely to limit the potential of populations to adapt to changing environmental conditions. Our study provides direct evidence of self-incompatibility (heterothallism) in L. pulmonaria. It can thus be hypothesized that sexual reproduction in small populations might be limited by an unbalanced distribution of mating-type genes. We therefore assessed neutral genetic diversity (using microsatellites) and mating-type ratio in 27 lichen populations (933 individuals). We found significant differences in the frequency of the two mating types in 13 populations, indicating a lower likelihood of sexual reproduction in these populations. This suggests that conservation translocation activities aiming at maximizing genetic heterogeneity in threatened and declining populations should take into account not only presence of fruiting bodies in transplanted individuals, but also the identity and balanced representation of mating-type genes.

Singh, Garima; Dal Grande, Francesco; Cornejo, Carolina; Schmitt, Imke; Scheidegger, Christoph

2012-01-01

95

Distribution of the Sex-Determining Gene MID and Molecular Correspondence of Mating Types within the Isogamous Genus Gonium (Volvocales, Chlorophyta)  

PubMed Central

Background Isogamous organisms lack obvious cytological differences in the gametes of the two complementary mating types. Consequently, it is difficult to ascertain which of the two mating types are homologous when comparing related but sexual isolated strains or species. The colonial volvocalean algal genus Gonium consists of such isogamous organisms with heterothallic mating types designated arbitrarily as plus or minus in addition to homothallic strains. Homologous molecular markers among lineages may provide an “objective” framework to assign heterothallic mating types. Methodology/Principal Findings Using degenerate primers designed based on previously reported MID orthologs, the “master regulator” of mating types/sexes in the colonial Volvocales, MID homologs were identified and their presence/absence was examined in nine strains of four species of Gonium. Only one of the two complementary mating types in each of the four heterothallic species has a MID homolog. In addition to heterothallic strains, a homothallic strain of G. multicoccum has MID. Molecular evolutionary analysis suggests that MID of this homothallic strain retains functional constraint comparable to that of the heterothallic strains. Conclusion/Significance We coordinated mating genotypes based on presence or absence of a MID homolog, respectively, in heterothallic species. This scheme should be applicable to heterothallic species of other isogamous colonial Volvocales including Pandorina and Yamagishiella. Homothallism emerged polyphyletically in the colonial Volvocales, although its mechanism remains unknown. Our identification of a MID homolog for a homothallic strain of G. multicoccum suggests a MID-dependent mechanism is involved in the sexual developmental program of this homothallic species.

Hamaji, Takashi; Ferris, Patrick J.; Nishii, Ichiro; Nishimura, Yoshiki; Nozaki, Hisayoshi

2013-01-01

96

Mating-type control in Saccharomyces cerevisiae: isolation and characterization of mutants defective in repression by a1-alpha 2.  

PubMed Central

The alpha 2 protein, the product of the MAT alpha 2 cistron, represses various genes specific to the a mating type (alpha 2 repression), and when combined with the MATa1 gene product, it represses MAT alpha 1 and various haploid-specific genes (a1-alpha 2 repression). One target of a1-alpha 2 repression is RME1, which is a negative regulator of a/alpha-specific genes. We have isolated 13 recessive mutants whose a1-alpha 2 repression is defective but which retain alpha 2 repression in a genetic background of ho MATa HML alpha HMRa sir3 or ho MAT alpha HMRa HMRa sir3. These mutations can be divided into three different classes. One class contains a missense mutation, designated hml alpha 2-102, in the alpha 2 cistron of HML, and another class contains two mat alpha 2-202, in the MAT alpha locus. These three mutants each have an amino acid substitution of tyrosine or acid substitution of tyrosine or phenylalanine for cysteine at the 33rd codon from the translation initiation codon in the alpha 2 cistron of HML alpha or MAT alpha. The remaining 10 mutants make up the third class and form a single complementation group, having mutations designated aar1 (a1-alpha 2 repression), at a gene other than MAT, HML, HMR, RME1, or the four SIR genes. Although a diploid cell homozygous for the aarl and sir3 mutations and for the MATa, HML alpha, and HMRa alleles showed alpha mating type, it could sporulate and gave rise to asci containing four alpha mating-type spores. These facts indicate that the domain for alpha2 repression is separable from that for a1-alpha2 protein interaction or complex formation in the alpha2 protein and that an additional regulation gene, AAR1, is associated with the a1-alpha2 repression of the alpha1 cistron and haploid-specific genes. Images

Harashima, S; Miller, A M; Tanaka, K; Kusumoto, K; Tanaka, K; Mukai, Y; Nasmyth, K; Oshima, Y

1989-01-01

97

Isolation and characterization of the mating-type idiomorphs from the wheat septoria leaf blotch fungus Mycosphaerella graminicola.  

PubMed

Both mating-type loci from the wheat septoria leaf blotch pathogen Mycosphaerella graminicola have been cloned and sequenced. The MAT1-2 gene was identified by screening a genomic library from the MAT1-2 isolate IPO94269 with a heterologous probe from Tapesia yallundae. The MAT1-2 idiomorph is 2772 bp and contains a single gene encoding a putative high-mobility-group protein of 394 amino acids. The opposite idiomorph was obtained from isolate IPO323, which has the complementary mating type, by long-range PCR using primers derived from sequences flanking the MAT1-2 idiomorph. The MAT1-1 locus is 2839 bp in size and contains a single open reading frame encoding a putative alpha1-domain protein of 297 amino acids. Within the nonidiomorphic sequences, homology was found with palI, encoding a membrane receptor from Aspergillus nidulans, and a gene encoding a putative component of the anaphase-promoting complex from Schizosaccharomyces pombe and a DNA-(apurinic or apyrimidinic) lyase from S. pombe. For each of the MAT genes specific primers were designed and tested on an F1 mapping population that was generated from a cross between IPO323 and IPO94269. An absolute correlation was found between the amplified allele-specific fragments and the mating type as determined by backcrosses of each F1 progeny isolate to the parental isolates. The primers were also used to screen a collection of field isolates in a multiplex PCR. An equal distribution of MAT1-1 and MAT1-2 alleles was found for most geographic origins examined. PMID:11929216

Waalwijk, Cees; Mendes, Odette; Verstappen, Els C P; de Waard, Maarten A; Kema, Gert H J

2002-04-01

98

The Ustilago maydis b mating type locus controls hyphal proliferation and expression of secreted virulence factors in planta.  

PubMed

Sexual development in fungi is controlled by mating type loci that prevent self-fertilization. In the phytopathogenic fungus Ustilago maydis, the b mating type locus encodes two homeodomain proteins, termed bE and bW. After cell fusion, a heterodimeric bE/bW complex is formed if the proteins are derived from different alleles. The bE/bW complex is required and sufficient to initiate pathogenic development and sexual reproduction; for the stages of pathogenic development succeeding plant penetration, however, its role was unclear. To analyse b function during in planta development, we generated a temperature-sensitive bE(ts) protein by exchange of a single amino acid. bE(ts) strains are stalled in pathogenic development at restrictive temperature in planta, and hyphae develop enlarged, bulbous cells at their tips that contain multiple nuclei, indicating a severe defect in the control and synchronization of cell cycle and cytokinesis. DNA array analysis of bE(ts) mutant strains in planta revealed a b-dependent regulation of genes encoding secreted proteins that were shown to influence fungal virulence. Our data demonstrate that in U. maydis the b heterodimer is not only essential to establish the heterodikaryon after mating of two compatible sporidia and to initiate fungal pathogenicity, but also to sustain in planta proliferation and ensure sexual reproduction. PMID:19943901

Wahl, Ramon; Zahiri, Alexander; Kämper, Jörg

2010-01-01

99

Mating Type Locus of Chinese Black Truffles Reveals Heterothallism and the Presence of Cryptic Species within the T. indicum Species Complex  

PubMed Central

Tuber spp. are filamentous ascomycetes which establish symbiosis with the roots of trees and shrub species. By virtue of this symbiosis they produce hypogeous ascocarps, known as truffles. Filamentous ascomycetes can reproduce by homothallism or heterothallism depending on the structure and organization of their mating type locus. The first mating type locus in a truffle species has been recently characterized in Tuber melanosporum and it has been shown that this fungus, endemic in Europe, is heterothallic. The availability of sequence information for T. melanosporum mating type genes is seminal to cloning their orthologs from other Tuber species and assessing their reproductive mode. Here we report on the organization of the mating type region in T. indicum, the black truffle species present in Asia, which is the closest relative to T. melanosporum and is characterized by an high level of morphological and genetic variability. The present study shows that T. indicum is also heterothallic. Examination of Asiatic black truffles belonging to different genetic classes, sorted according to the sequence polymorphism of the internal transcribed spacer rDNA region, has revealed sequence variations and rearrangements in both coding and non-coding regions of the mating type locus, to suggest the existence of cryptic species within the T. indicum complex. The presence of transposable elements within or linked to the mating type region suggests a role of these elements in generating the genotypic diversity present among T. indicum strains. Overall, comparative analyses of the mating type locus have thus allowed us to tackle taxonomical and phylogenetic issues within black truffles and make inferences about the evolution of T. melanosporum-T. indicum lineage. Our results are not only of fundamental but also of applied relevance as T. indicum produces edible fruit bodies that are imported also into Europe and thus may represent a biological threat for T. melanosporum.

Belfiori, Beatrice; Riccioni, Claudia; Paolocci, Francesco; Rubini, Andrea

2013-01-01

100

Mating type locus of Chinese black truffles reveals heterothallism and the presence of cryptic species within the T. indicum species complex.  

PubMed

Tuber spp. are filamentous ascomycetes which establish symbiosis with the roots of trees and shrub species. By virtue of this symbiosis they produce hypogeous ascocarps, known as truffles. Filamentous ascomycetes can reproduce by homothallism or heterothallism depending on the structure and organization of their mating type locus. The first mating type locus in a truffle species has been recently characterized in Tuber melanosporum and it has been shown that this fungus, endemic in Europe, is heterothallic. The availability of sequence information for T. melanosporum mating type genes is seminal to cloning their orthologs from other Tuber species and assessing their reproductive mode. Here we report on the organization of the mating type region in T. indicum, the black truffle species present in Asia, which is the closest relative to T. melanosporum and is characterized by an high level of morphological and genetic variability. The present study shows that T. indicum is also heterothallic. Examination of Asiatic black truffles belonging to different genetic classes, sorted according to the sequence polymorphism of the internal transcribed spacer rDNA region, has revealed sequence variations and rearrangements in both coding and non-coding regions of the mating type locus, to suggest the existence of cryptic species within the T. indicum complex. The presence of transposable elements within or linked to the mating type region suggests a role of these elements in generating the genotypic diversity present among T. indicum strains. Overall, comparative analyses of the mating type locus have thus allowed us to tackle taxonomical and phylogenetic issues within black truffles and make inferences about the evolution of T. melanosporum-T. indicum lineage. Our results are not only of fundamental but also of applied relevance as T. indicum produces edible fruit bodies that are imported also into Europe and thus may represent a biological threat for T. melanosporum. PMID:24358175

Belfiori, Beatrice; Riccioni, Claudia; Paolocci, Francesco; Rubini, Andrea

2013-01-01

101

The transcription factor Rbf1 is the master regulator for b-mating type controlled pathogenic development in Ustilago maydis.  

PubMed

In the phytopathogenic basidiomycete Ustilago maydis, sexual and pathogenic development are tightly connected and controlled by the heterodimeric bE/bW transcription factor complex encoded by the b-mating type locus. The formation of the active bE/bW heterodimer leads to the formation of filaments, induces a G2 cell cycle arrest, and triggers pathogenicity. Here, we identify a set of 345 bE/bW responsive genes which show altered expression during these developmental changes; several of these genes are associated with cell cycle coordination, morphogenesis and pathogenicity. 90% of the genes that show altered expression upon bE/bW-activation require the zinc finger transcription factor Rbf1, one of the few factors directly regulated by the bE/bW heterodimer. Rbf1 is a novel master regulator in a multilayered network of transcription factors that facilitates the complex regulatory traits of sexual and pathogenic development. PMID:20700446

Heimel, Kai; Scherer, Mario; Vranes, Miroslav; Wahl, Ramon; Pothiratana, Chetsada; Schuler, David; Vincon, Volker; Finkernagel, Florian; Flor-Parra, Ignacio; Kämper, Jörg

2010-01-01

102

The Transcription Factor Rbf1 Is the Master Regulator for b-Mating Type Controlled Pathogenic Development in Ustilago maydis  

PubMed Central

In the phytopathogenic basidiomycete Ustilago maydis, sexual and pathogenic development are tightly connected and controlled by the heterodimeric bE/bW transcription factor complex encoded by the b-mating type locus. The formation of the active bE/bW heterodimer leads to the formation of filaments, induces a G2 cell cycle arrest, and triggers pathogenicity. Here, we identify a set of 345 bE/bW responsive genes which show altered expression during these developmental changes; several of these genes are associated with cell cycle coordination, morphogenesis and pathogenicity. 90% of the genes that show altered expression upon bE/bW-activation require the zinc finger transcription factor Rbf1, one of the few factors directly regulated by the bE/bW heterodimer. Rbf1 is a novel master regulator in a multilayered network of transcription factors that facilitates the complex regulatory traits of sexual and pathogenic development.

Vranes, Miroslav; Wahl, Ramon; Pothiratana, Chetsada; Schuler, David; Vincon, Volker; Finkernagel, Florian; Flor-Parra, Ignacio; Kamper, Jorg

2010-01-01

103

A sex recognition glycoprotein is encoded by the plus mating-type gene fus1 of Chlamydomonas reinhardtii.  

PubMed Central

Sexual fusion between plus and minus gametes of the unicellular green alga Chlamydomonas reinhardtii entails adhesion between plus-specific and minus-specific "fringe" proteins displayed on the plasma membrane of gametic mating structures. We report the identification of the gene (fus1) encoding the plus fringe glycoprotein, which resides in a unique domain of the mating-type plus (mt+) locus, and which was identified by transposon insertions in three fusion-defective mutant strains. Transformation with fus1+ restores fringe and fusion competence to these mutants and to the pseudo-plus mutant imp11 mt-, defective in minus differentiation. The fus1 gene is remarkable in lacking the codon bias found in all other nuclear genes of C. reinhardtii. Images

Ferris, P J; Woessner, J P; Goodenough, U W

1996-01-01

104

Genotype and mating type analysis of Cryptococcus neoformans and Cryptococcus gattii isolates from China that mainly originated from non-HIV-infected patients.  

PubMed

Cryptococcosis has been reported to be mostly associated with non-HIV-related patients in China. However, little is known about the molecular characteristics of clinical isolates from the Cryptococcus neoformans species complex in this country. In this study, 115 clinical isolates were included. Molecular type VNI was the most representative (n=103), followed by VGI (n=8), VNIII (n=2), VNIV (n=1), and VGII (n=1). With the exception of a serotype D mating type a isolate, all possessed the MATalpha locus. Multilocus sequence typing (MLST) revealed that most Cryptococcus gattii isolates from China shared identical MLST profiles with the most common MLST genotype reported in the VGI group, and the only one VGII isolate resembled the Vancouver Island outbreak minor genotype. The C. gattii strains involved in this study were successfully grouped according to their molecular type and mating types by PCR-restriction fragment length polymorphism (RFLP) analysis of the GEF1 gene. Our results suggest that (1) in China, cryptococcosis is mostly caused by C. neoformans var. grubii (molecular type VNI), and mating type alpha; (2) The most common causative agents of C. gattii infection in China are closely related to a widely distributed MLST genotype; and (3) The PCR-RFLP analysis of the GEF1 gene has the potential to identify the molecular and mating types of C. gattii simultaneously. PMID:18671745

Feng, Xiaobo; Yao, Zhirong; Ren, Daming; Liao, Wanqing; Wu, Jingsong

2008-09-01

105

Microtubule Dynamics from Mating through the First Zygotic Division in the Budding Yeast Saccharomyces cerevisiae  

Microsoft Academic Search

We have used time-lapse digital imaging mi- croscopy to examine cytoplasmic astral microtubules (Mts) and spindle dynamics during the mating pathway in budding yeast Saccharomyces cerevisiae . Mating be- gins when two cells of opposite mating type come into proximity. The cells arrest in the G1 phase of the cell cy- cle and grow a projection towards one another forming

Paul Maddox; E. Chin; A. Mallavarapu; E. Yeh; E. D. Salmon; K. Bloom

1999-01-01

106

Phylogeny and evolution of mating-type genes from Pyrenophora teres, the causal agent of barley "net blotch" disease.  

PubMed

The main aim of this study was to test the patterns of sequence divergence and haplotype structure at the MAT locus of Pyrenophora teres, the causal agent of barley 'net blotch' disease. P. teres is a heterothallic ascomycete that co-occurs in two symptomatological forms, the net form (NF) and the spot form (SF). The mating-type genes MAT1-1-1 and MAT1-2-1 were sequenced from 22 NF isolates (12 MAT1-1-1 and 10 MAT1-2-1 sequences) and 17 SF isolates (10 MAT1-1-1 and seven MAT1-2-1 sequences) collected from Sardinian barley landrace populations and worldwide. On the basis of a parsimony network analysis, the two forms of P. teres are phylogenetically separated. More than 85% of the total nucleotide variation was found between formae speciales. The two forms do not share any polymorphisms. Six diagnostic nucleotide polymorphisms were found in the MAT1-1-1 intron (1) and in the MAT1-1-1 (3) and MAT1-2-1 (2) exons. Three diagnostic non-synonymous mutations were found, one in MAT1-1-1 and two in MAT1-2-1. For comparison with P. teres sequence data, the mating-type genes from Pyrenophora graminea were also isolated and sequenced. Divergence between P. graminea and P. teres is of a similar magnitude to that between NF and SF of P. teres. The MAT genes of P. graminea were closer to those of SF than to NF, with the MAT1-2-1 SF peptide not different from the MAT1-2-1 peptide of P. graminea. Overall, these data suggest long genetic isolation between the two forms of P. teres and that hybridization is rare or absent under field conditions, with each form having some particular niche specialization. This indicates that research on resistance to P. teres should consider the two forms separately, as different species. PMID:17426975

Rau, D; Attene, G; Brown, A H D; Nanni, L; Maier, F J; Balmas, V; Saba, E; Schäfer, W; Papa, R

2007-06-01

107

Commercial Fungicide Formulations Induce In Vitro Oospore Formation and Phenotypic Change in Mating Type in Phytophthora infestans.  

PubMed

ABSTRACT A wide range of commercially formulated fungicides cause in vitro effects on mating behavior in specific isolates of Phytophthora infestans, the causal agent of late blight of potato and tomato. Four isolates of P. infestans representing each of the four common US genotypes, US-1, US-6, US-7, and US-8 and varying in their sensitivity to metalaxyl, were exposed to a variety of fungicides used to control late blight in petri dish assays at concentrations ranging from 1 to 100 mug a.i./ml. Exposure of each of these normally heterothallic single mating type isolates of P. infestans to 9 of the 11 commercial fungicide formulations tested resulted in the formation of oospores after 2 to 4 weeks. The highest numbers of oospores were formed on media amended with Ridomil 2E (metalaxyl) and Ridomil Gold EC (mefenoxam) at 0.1 to 10 mug a.i./ml, averaging as many as 471 and 450 oospores per petri dish, respectively. Several other fungicides including Maneb, Manzate (Mancozeb), Curzate (cymoxanil + mancozeb), and Acrobat MZ (dimethomorph + mancozeb) also induced oospore formation, producing from 0 to 200 oospores per plate at fungicide concentrations from 0.1 to 10 mug a.i./ml. The metalaxyl resistant isolates formed oospores in response to the fungicides more often than the metalaxyl sensitive isolates. No oospores were formed on media amended with Bravo (chlorothalonil) or Tattoo C (chlorothalonil + propamocarb HCl) and these compounds completely suppressed growth of the isolates at 0.1 and 1 mug a.i./ml. Three metalaxyl resistant A2 isolates mated with both A1 and A2 isolates after exposure to the fungicides Ridomil 2E and Ridomil Gold EC. Alterations in mating type expression were also observed in a metalaxyl sensitive A1 isolate after exposure to Benlate (benomyl). Copious amounts of chemicals are applied annually to potato and tomato production areas to control late blight. Our results indicate that a wide range of chemically diverse fungicides can induce normally heterothallic metalaxyl resistant isolates of P. infestans to form oospores in vitro after short exposures to the fungicides. PMID:18944421

Groves, C T; Ristaino, J B

2000-11-01

108

Mating type idiomorphs from a French population of the wheat pathogen Mycosphaerella graminicola: widespread equal distribution and low but distinct levels of molecular polymorphism.  

PubMed

Septoria tritici blotch caused by the heterothallic ascomycete Mycosphaerella graminicola is currently the most frequent and the most economically damaging disease on wheat worldwide. Five hundred and ten strains of this fungus were sampled from 16 geographical locations representing the major wheat producing areas in France. Multiplex PCR amplification, PCR-RFLP-SSCP screening and sequencing of parts of mating type encoding sequences were performed in order to assess the distribution and molecular polymorphism of the mating type idiomorphs. The two idiomorphs were scored at similar frequencies within all sampled locations. Both mating types were also identified at the leaf spatial scale, on 42% of leaves from which two or three strains were isolated. No correlation was found between distribution of mating types and either host cultivars from which the sampling was carried out or in vitro colony phenotypes observed during the culture of strains on potato dextrose agar (PDA) medium. PCR-RFLP-SSCP assay highlighted only one MAT1-1 strain exhibiting a profile distinct from all other MAT1-1 strains, whereas ten MAT1-2 strains (among which two and four with same profiles, respectively) showed profiles differing from the other MAT1-2 strains. Sequencing revealed that all polymorphisms corresponded to single nucleotide variations and all strains displaying the same single strand conformation polymorphism (SSCP) profiles showed identical nucleotide sequences, thereby confirming the high sensitivity of SSCP. Only two out of the disclosed nucleotide variations were nonsynonymous. This study strongly suggests a large potential for sexual reproduction in the French population of M. graminicola and reports a high conservation of mating type sequences in the fungus at both nucleotide and population levels, with a great difference in molecular variability between the two idiomorphs. PMID:21036342

Siah, Ali; Tisserant, Benoit; El Chartouni, Léa; Duyme, Florent; Deweer, Caroline; Roisin-Fichter, Céline; Sanssené, Jean; Durand, Roger; Reignault, Philippe; Halama, Patrice

2010-01-01

109

Genetic diversity and mating types of Fusarium culmorum and Fusarium graminearum originating from different agro-ecological regions in Turkey.  

PubMed

Fusarium culmorum and F. graminearum are the major pathogens for dryland root/foot-rot and head-blight diseases in economically important grain crops. This study was aimed at the molecular characterization of Fusarium spp. isolates, which have been collected from cereal fields in three agro-ecological regions in Turkey. Genetic diversity has been analyzed by generating RFLP markers from the intergenic spacer (IGS) region of ribosomal RNA. The selection of restriction enzymes for IGS-RFLP studies has been found critical to maximize polymorphic markers. Only 3 of 14 restriction endonucleases were useful in differentiating Fusarium spp. isolates. PstI was the most efficient enzyme to produce a maximum of nine DNA markers in one individual and total 22 polymorphic representative banding patterns. Polymorphism based on IGS-RFLP was high and average 88% in both species. There was no association between IGS diversity and geographic locations from which the samples were taken. Both MAT-1 and MAT-2 sequences were amplified in F. graminearum similarly to previous reports. Most of the F. culmorum isolates carried either MAT-1 or MAT-2 sequences, and differently two isolates carried both sequences. Mating type determination was helpful to distinguish F. pseudograminearum from F. graminearum, which cannot be discriminated by SCAR markers or morphological assessment. High genetic diversity by IGS-RFLP markers in F. culmorum was discussed in relation to its fitness as the most common pathogen in dryland root rot complex (DLRRC). PMID:22961691

Çepni, Elif; Tunal?, Berna; Gürel, Filiz

2013-08-01

110

Characterization of mat A-2, mat A-3 and deltamatA mating-type mutants of Neurospora crassa.  

PubMed Central

The mating-type locus of Neurospora crassa regulates mating identity and entry into the sexual cycle. The mat A idiomorph encodes three genes, mat A-1, mat A-2, and mat A-3. Mutations in mat A-1 result in strains that have lost mating identity and vegetative incompatibility with mat a strains. A strain containing mutations in both mat A-2 and mat A-3 is able to mate, but forms few ascospores. In this study, we describe the isolation and characterization of a mutant deleted for mat (deltamatA), as well as mutants in either mat A-2 or mat A-3. The deltamatA strain is morphologically wild type during vegetative growth, but it is sterile and heterokaryon compatible with both mat A and mat a strains. The mat A-2 and mat A-3 mutants are also normal during vegetative growth, mate as a mat A strain, and produce abundant biparental asci in crosses with mat a, and are thus indistinguishable from a wild-type mat A strain. These data and the fact that the mat A-2 mat A-3 double mutant makes few asci with ascospores indicate that MAT A-2 and MAT A-3 are redundant and may function in the same pathway. Analysis of the expression of two genes (sdv-1 and sdv-4) in the various mat mutants suggests that the mat A polypeptides function in concert to regulate the expression of some sexual development genes.

Ferreira, A V; An, Z; Metzenberg, R L; Glass, N L

1998-01-01

111

Degeneration in Codon Usage within the Region of Suppressed Recombination in the Mating-Type Chromosomes of Neurospora tetrasperma ? †  

PubMed Central

The origin and early evolution of sex chromosomes are currently poorly understood. The Neurospora tetrasperma mating-type (mat) chromosomes have recently emerged as a model system for the study of early sex chromosome evolution, since they contain a young (<6 million years ago [Mya]), large (>6.6-Mb) region of suppressed recombination. Here we examined preferred-codon usage in 290 genes (121,831 codon positions) in order to test for early signs of genomic degeneration in N. tetrasperma mat chromosomes. We report several key findings about codon usage in the region of recombination suppression, including the following: (i) this region has been subjected to marked and largely independent degeneration among gene alleles; (ii) the level of degeneration is magnified over longer periods of recombination suppression; and (iii) both mat a and mat A chromosomes have been subjected to deterioration. The frequency of shifts from preferred codons to nonpreferred codons is greater for shorter genes than for longer genes, suggesting that short genes play an especially significant role in early sex chromosome evolution. Furthermore, we show that these degenerative changes in codon usage are best explained by altered selection efficiency in the recombinationally suppressed region. These findings demonstrate that the fungus N. tetrasperma provides an effective system for the study of degenerative genomic changes in young regions of recombination suppression in sex-regulating chromosomes.

Whittle, C. A.; Sun, Y.; Johannesson, H.

2011-01-01

112

ATP Binding to Hemoglobin Response Gene 1 Protein Is Necessary for Regulation of the Mating Type Locus in Candida albicans*  

PubMed Central

HBR1 (hemoglobin response gene 1) is an essential gene in Candida albicans that positively regulates mating type locus MTL? gene expression and thereby regulates cell type-specific developmental genes. Hbr1p contains a phosphate-binding loop (P-loop), a highly conserved motif characteristic of ATP- and GTP-binding proteins. Recombinant Hbr1p was isolated in an oligomeric state that specifically bound ATP with Kd ?2 ?m. ATP but not ADP, AMP, GTP, or dATP specifically protected Hbr1p from proteolysis by trypsin. Site-directed mutagenesis of the highly conserved P-loop lysine (K22Q) and the less conserved glycine (G19S) decreased the binding affinity for soluble ATP and ATP immobilized through its ?-phosphate. ATP bound somewhat more avidly than ATP?S to wild type and mutant Hbr1p. Although Hbr1p exhibits sequence motifs characteristic of adenylate kinases, and adenylate kinase and ATPase activities have been reported for the apparent human ortholog of Hbr1p, assays for adenylate kinase activity, autophosphorylation, and ATPase activity proved negative. Overexpression of wild type but not the mutant forms of Hbr1p restored MTl?2 expression in an HBR1/hbr1 mutant, indicating that ATP binding to the P-loop is necessary for this function of Hbr1p.

Peterson, Alexander W.; Pendrak, Michael L.; Roberts, David D.

2011-01-01

113

Breeding of high ergosterol-producing yeast strains  

Microsoft Academic Search

  High ergosterol-producing yeast strains YEH-28 and YEH-56 were constructed by hybridization of two haploids with opposite\\u000a mating types from different species. The fermentation conditions of hybrid strain YEH-56 were studied. The highest level of\\u000a ergosterol was obtained in 30 h at 28°C and 200 rpm, when 60 ml of culture in 250-ml shake flasks was grown in fermentation\\u000a medium that

X He; W Huai; C Tie; Y Liu; B Zhang

2000-01-01

114

Large-Scale Introgression Shapes the Evolution of the Mating-Type Chromosomes of the Filamentous Ascomycete Neurospora tetrasperma  

PubMed Central

The significance of introgression as an evolutionary force shaping natural populations is well established, especially in animal and plant systems. However, the abundance and size of introgression tracts, and to what degree interspecific gene flow is the result of adaptive processes, are largely unknown. In this study, we present medium coverage genomic data from species of the filamentous ascomycete Neurospora, and we use comparative genomics to investigate the introgression landscape at the genomic level in this model genus. We revealed one large introgression tract in each of the three investigated phylogenetic lineages of Neurospora tetrasperma (sizes of 5.6 Mbp, 5.2 Mbp, and 4.1 Mbp, respectively). The tract is located on the chromosome containing the locus conferring sexual identity, the mating-type (mat) chromosome. The region of introgression is confined to the region of suppressed recombination and is found on one of the two mat chromosomes (mat a). We used Bayesian concordance analyses to exclude incomplete lineage sorting as the cause for the observed pattern, and multilocus genealogies from additional species of Neurospora show that the introgression likely originates from two closely related, freely recombining, heterothallic species (N. hispaniola and N. crassa/N. perkinsii). Finally, we investigated patterns of molecular evolution of the mat chromosome in Neurospora, and we show that introgression is correlated with reduced level of molecular degeneration, consistent with a shorter time of recombination suppression. The chromosome specific (mat) and allele specific (mat a) introgression reported herein comprise the largest introgression tracts reported to date from natural populations. Furthermore, our data contradicts theoretical predictions that introgression should be less likely on sex-determining chromosomes. Taken together, the data presented herein advance our general understanding of introgression as a force shaping eukaryotic genomes.

Menkis, Audrius; Whittle, Carrie A.; Andersson, Siv G. E.; Johannesson, Hanna

2012-01-01

115

Evolution of the Mating Type Locus: Insights Gained from the Dimorphic Primary Fungal Pathogens Histoplasma capsulatum, Coccidioides immitis, and Coccidioides posadasii? †  

PubMed Central

Sexual reproduction of fungi is governed by the mating type (MAT) locus, a specialized region of the genome encoding key transcriptional regulators that direct regulatory networks to specify cell identity and fate. Knowledge of MAT locus structure and evolution has been considerably advanced in recent years as a result of genomic analyses that enable the definition of MAT locus sequences in many species as well as provide an understanding of the evolutionary plasticity of this unique region of the genome. Here, we extend this analysis to define the mating type locus of three dimorphic primary human fungal pathogens, Histoplasma capsulatum, Coccidioides immitis, and Coccidioides posadasii, using genomic analysis, direct sequencing, and bioinformatics. These studies provide evidence that all three species possess heterothallic bipolar mating type systems, with isolates encoding either a high-mobility-group (HMG) domain or an ?-box transcriptional regulator. These genes are intact in all loci examined and have not been subject to loss or decay, providing evidence that the loss of fertility upon passage in H. capsulatum is not attributable to mutations at the MAT locus. These findings also suggest that an extant sexual cycle remains to be defined in both Coccidioides species, in accord with population genetic evidence. Based on these MAT sequences, a facile PCR test was developed that allows the mating type to be rapidly ascertained. Finally, these studies highlight the evolutionary forces shaping the MAT locus, revealing examples in which flanking genes have been inverted or subsumed and incorporated into an expanding MAT locus, allowing us to propose an expanded model for the evolution of the MAT locus in the phylum Ascomycota.

Fraser, James A.; Stajich, Jason E.; Tarcha, Eric J.; Cole, Garry T.; Inglis, Diane O.; Sil, Anita; Heitman, Joseph

2007-01-01

116

The Yeast Deletion Collection: A Decade of Functional Genomics  

PubMed Central

The yeast deletion collections comprise >21,000 mutant strains that carry precise start-to-stop deletions of ?6000 open reading frames. This collection includes heterozygous and homozygous diploids, and haploids of both MATa and MAT? mating types. The yeast deletion collection, or yeast knockout (YKO) set, represents the first and only complete, systematically constructed deletion collection available for any organism. Conceived during the Saccharomyces cerevisiae sequencing project, work on the project began in 1998 and was completed in 2002. The YKO strains have been used in numerous laboratories in >1000 genome-wide screens. This landmark genome project has inspired development of numerous genome-wide technologies in organisms from yeast to man. Notable spinoff technologies include synthetic genetic array and HIPHOP chemogenomics. In this retrospective, we briefly describe the yeast deletion project and some of its most noteworthy biological contributions and the impact that these collections have had on the yeast research community and on genomics in general.

Giaever, Guri; Nislow, Corey

2014-01-01

117

Impact of the competition between mating types on the cultivation of Tuber melanosporum: Romeo and Juliet and the matter of space and time.  

PubMed

Major breakthroughs in our understanding of the life cycles of the symbiotic ascomycetes belonging to the genus Tuber have occurred over the last several years. A number of Tuber species produce edible fruiting bodies, known as truffles, that are marketed worldwide. A better understanding of the basic biological characteristics of Tuber spp. is likely to have tremendous practical relevance for their cultivation. Tuber melanosporum produces the most valuable black truffles and its genome has been recently sequenced. This species is now serving as a model for studying the biology of truffles. Here, we review recent progress in the understanding of sexual reproduction modalities in T. melanosporum. The practical relevance of these findings is outlined. In particular, the discoveries that T. melanosporum is heterothallic and that strains of different mating types compete to persist on the roots of host plants suggest that the spatial and temporal distributional patterns of strains of different mating types are key determinants of truffle fructification. The spatial segregation of the two mating types in areas where T. melanosporum occurs likely limits truffle production. Thus, host plant inoculation techniques and agronomic practices that might be pursued to manage T. melanosporum orchards with a balanced presence of the two mating partners are described. PMID:24384788

Rubini, Andrea; Riccioni, Claudia; Belfiori, Beatrice; Paolocci, Francesco

2014-04-01

118

Prion-Dependent Switching between Respiratory Competence and Deficiency in the Yeast nam9-1 Mutant  

PubMed Central

Nam9p is a protein of the mitochondrial ribosome. The respiration-deficient Saccharomyces cerevisiae strain MB43-nam9-1 expresses Nam9-1p containing the point mutation S82L. Respiratory deficiency correlates with a decrease in the steady level of some mitochondrially encoded proteins and the complete lack of mitochondrially encoded cytochrome oxidase subunit 2 (Cox2). De novo synthesis of Cox2 in MB43-nam9-1 is unaffected, indicating that newly synthesized Cox2 is rapidly degraded. Respiratory deficiency of MB43-nam9-1 is overcome by transient overexpression of HSP104, by deletion of HSP104, by transient exposure to guanidine hydrochloride, and by expression of the C-terminal portion of Sup35, indicating an involvement of the yeast prion [PSI+]. Respiratory deficiency of MB43-nam9-1 can be reinduced by transfer of cytosol from S. cerevisiae that harbors [PSI+]. We conclude that nam9-1 causes respiratory deficiency only in combination with the cytosolic prion [PSI+], presenting the first example of a synthetic effect between cytosolic [PSI+] and a mutant mitochondrial protein.

Chacinska, Agnieszka; Boguta, Magdalena; Krzewska, Joanna; Rospert, Sabine

2000-01-01

119

Serotype AD Strains of Cryptococcus neoformans Are Diploid or Aneuploid and Are Heterozygous at the Mating-Type Locus  

Microsoft Academic Search

Cryptococcus neoformans is a pathogenic basidiomycete with a defined sexual cycle involving mating between haploid yeast cells with a transient diploid state. C. neoformans occurs in four predominant serotypes (A, B, C, and D), which represent different varieties or species. Rare clinical and environmental isolates with an unusual AD serotype have been reported and suggested to be diploid. We found

KLAUS B. LENGELER; GARY M. COX; JOSEPH HEITMAN

2001-01-01

120

Genetic Diversity and Mating Type Distribution of Tuber melanosporum and Their Significance to Truffle Cultivation in Artificially Planted Truffi?res in Australia  

PubMed Central

Tuber melanosporum is a truffle native to Europe and is cultivated in countries such as Australia for the gastronomic market, where production yields are often lower than expected. We assessed the genetic diversity of T. melanosporum with six microsatellite loci to assess the effect of genetic drift on truffle yield in Australia. Genetic diversity as assessed on 210 ascocarps revealed a higher allelic diversity compared to previous studies from Europe, suggesting a possible genetic expansion and/or multiple and diverse source populations for inoculum. The results also suggest that the single sequence repeat diversity of locus ME2 is adaptive and that, for example, the probability of replication errors is increased for this locus. Loss of genetic diversity in Australian populations is therefore not a likely factor in limiting ascocarp production. A survey of nursery seedlings and trees inoculated with T. melanosporum revealed that <70% of seedlings and host trees were colonized with T. melanosporum and that some trees had been contaminated by Tuber brumale, presumably during the inoculation process. Mating type (MAT1-1-1 and MAT1-2-1) analyses on seedling and four- to ten-year-old host trees found that 100% of seedlings but only approximately half of host trees had both mating types present. Furthermore, MAT1-1-1 was detected significantly more commonly than MAT1-2-1 in established trees, suggesting a competitive advantage for MAT1-1-1 strains. This study clearly shows that there are more factors involved in ascocarp production than just the presence of both mating types on host trees.

Selmes, H.

2012-01-01

121

Genetic diversity and mating type distribution of Tuber melanosporum and their significance to truffle cultivation in artificially planted truffieres in Australia.  

PubMed

Tuber melanosporum is a truffle native to Europe and is cultivated in countries such as Australia for the gastronomic market, where production yields are often lower than expected. We assessed the genetic diversity of T. melanosporum with six microsatellite loci to assess the effect of genetic drift on truffle yield in Australia. Genetic diversity as assessed on 210 ascocarps revealed a higher allelic diversity compared to previous studies from Europe, suggesting a possible genetic expansion and/or multiple and diverse source populations for inoculum. The results also suggest that the single sequence repeat diversity of locus ME2 is adaptive and that, for example, the probability of replication errors is increased for this locus. Loss of genetic diversity in Australian populations is therefore not a likely factor in limiting ascocarp production. A survey of nursery seedlings and trees inoculated with T. melanosporum revealed that <70% of seedlings and host trees were colonized with T. melanosporum and that some trees had been contaminated by Tuber brumale, presumably during the inoculation process. Mating type (MAT1-1-1 and MAT1-2-1) analyses on seedling and four- to ten-year-old host trees found that 100% of seedlings but only approximately half of host trees had both mating types present. Furthermore, MAT1-1-1 was detected significantly more commonly than MAT1-2-1 in established trees, suggesting a competitive advantage for MAT1-1-1 strains. This study clearly shows that there are more factors involved in ascocarp production than just the presence of both mating types on host trees. PMID:22773652

Linde, C C; Selmes, H

2012-09-01

122

A Single Mating-Type Locus Composed of Homeodomain Genes Promotes Nuclear Migration and Heterokaryosis in the White-Rot Fungus Phanerochaete chrysosporium ? †  

PubMed Central

The white-rot basidiomycete fungus Phanerochaete chrysosporium (Agaricomycetes) is a model species that produces potent wood-degrading enzymes. The mating system of the species has been difficult to characterize due to its cryptic fruiting habit and lack of clamp connections in the heterokaryotic phase. By exploiting the draft genome sequence, we reevaluated the mating system of P. chrysosporium by studying the inheritance and segregation of putative mating-type gene homologues, the homeodomain transcription factor genes (MAT-A) and the pheromone receptors (MAT-B). A pattern of mating incompatibility and fructification consistent with a bipolar system with a single MAT locus was observed, but the rejection response was much weaker than that seen in other agaricomycete species, leading to stable heterokaryons with identical MAT alleles. The homeodomain genes appear to comprise the single MAT locus because they are heterozygous in wild strains and hyperpolymorphic at the DNA sequence level and promote aspects of sexual reproduction, such as nuclear migration, heterokaryon stability, and basidiospore formation. The pheromone receptor loci that might constitute a MAT-B locus, as in many other Agaricomycetes, are not linked to the MAT-A locus and display low levels of polymorphism. This observation is inconsistent with a bipolar mating system that includes pheromones and pheromone receptors as mating-type determinants. The partial uncoupling of nuclear migration and mating incompatibility in this species may be predicted to lead to parasexual recombination and may have contributed to the homothallic behavior observed in previous studies.

James, Timothy Y.; Lee, Maria; van Diepen, Linda T. A.

2011-01-01

123

Distribution of mating-type alleles and M13 PCR markers in the black leaf spot fungus Mycosphaerella fijiensis of bananas in Brazil.  

PubMed

The fungus Mycosphaerella fijiensis is the causative agent of black sigatoka, which is one of the most destructive diseases of banana plants. Infection with this pathogen results in underdeveloped fruit, with no commercial value. We analyzed the distribution of the M. fijiensis mating-type system and its genetic variability using M13 phage DNA markers. We found a 1:1 distribution of mating-type alleles, indicating MAT1-1 and MAT1-2 idiomorphs. A polymorphism analysis using three different primers for M13 markers showed that only the M13 minisatellite primers generated polymorphic products. We then utilized this polymorphism to characterize 40 isolates from various Brazilian states. The largest genetic distances were found between isolates from the same location and between isolates from different parts of the country. Therefore, there was no correlation between the genetic similarity and the geographic origin of the isolates. The M13 marker was used to generate genetic fingerprints for five isolates; these fingerprints were compared with the band profiles obtained from inter-simple sequence repeat (UBC861) and inter-retrotransposon amplified polymorphism analyses. We found that the M13 marker was more effective than the other two markers for differentiating these isolates. PMID:23420369

Queiroz, C B; Miranda, E C; Hanada, R E; Sousa, N R; Gasparotto, L; Soares, M A; Silva, G F

2013-01-01

124

A single mating-type locus composed of homeodomain genes promotes nuclear migration and heterokaryosis in the white-rot fungus Phanerochaete chrysosporium.  

PubMed

The white-rot basidiomycete fungus Phanerochaete chrysosporium (Agaricomycetes) is a model species that produces potent wood-degrading enzymes. The mating system of the species has been difficult to characterize due to its cryptic fruiting habit and lack of clamp connections in the heterokaryotic phase. By exploiting the draft genome sequence, we reevaluated the mating system of P. chrysosporium by studying the inheritance and segregation of putative mating-type gene homologues, the homeodomain transcription factor genes (MAT-A) and the pheromone receptors (MAT-B). A pattern of mating incompatibility and fructification consistent with a bipolar system with a single MAT locus was observed, but the rejection response was much weaker than that seen in other agaricomycete species, leading to stable heterokaryons with identical MAT alleles. The homeodomain genes appear to comprise the single MAT locus because they are heterozygous in wild strains and hyperpolymorphic at the DNA sequence level and promote aspects of sexual reproduction, such as nuclear migration, heterokaryon stability, and basidiospore formation. The pheromone receptor loci that might constitute a MAT-B locus, as in many other Agaricomycetes, are not linked to the MAT-A locus and display low levels of polymorphism. This observation is inconsistent with a bipolar mating system that includes pheromones and pheromone receptors as mating-type determinants. The partial uncoupling of nuclear migration and mating incompatibility in this species may be predicted to lead to parasexual recombination and may have contributed to the homothallic behavior observed in previous studies. PMID:21131435

James, Timothy Y; Lee, Maria; van Diepen, Linda T A

2011-02-01

125

Signal Transduction: Turning a Switch into a Rheostat  

PubMed Central

MAP kinase cascades are inherently switch-like, but, during yeast mating, MAPK signaling is graded. A new study suggests that the Ste5 scaffold protein is responsible for making this switch less switch-like.

Bardwell, Lee

2010-01-01

126

Genetically Controlled Self-Aggregation of Cell-Surface-Engineered Yeast Responding to Glucose Concentration  

Microsoft Academic Search

We constructed an arming (cell-surface-engineered) yeast displaying two types of agglutinin (modified a-agglutinin and a-agglutinin) on the cell surface, with agglutination being independent of both mating type and pheromones. The modified a-agglutinin was artificially prepared by the fusion of the genes encoding Aga1p and Aga2p. The modified a-agglutinin could induce agglutination of cells displaying Aga1p (a-agglutinin). The upstream region of

WEN ZOU; MITSUYOSHI UEDA; ATSUO TANAKA

2001-01-01

127

The histone deacetylase RPD3 counteracts genomic silencing in Drosophila and yeast  

Microsoft Academic Search

BOTH position-effect variegation (PEV)1,2 in Drosophila and telomeric position-effect in yeast (TPE)3-5 result from the mosaic inactivation of genes relocated next to a block of centromeric heterochromatin or next to telomeres. In many aspects, these phenomena are analogous to other epigenetic silencing mechan-isms, such as the control of homeotic gene clusters6, X-chromo-some inactivation7 and imprinting in mammals8, and mating-type control

Francesco De Rubertis; David Kadosh; Sandra Henchoz; Daniel Pauli; Gunter Reuter; Kevin Struhl; Pierre Spierer

1996-01-01

128

Rapid kinetics of mismatch repair of heteroduplex DNA that is formed during recombination in yeast.  

PubMed Central

Homothallic switching of yeast mating type (MAT) genes is a highly efficient gene conversion process initiated by a double-strand break. The use of a galactose-inducible HO endonuclease gene has made it possible to analyze the synchronous progression of molecular intermediates during recombination. When MATa switches to MAT alpha, a 3' single-stranded end of HO-cleaved MAT DNA invades the homologous donor, HML alpha, and initiates copying of new DNA sequences. These early steps of recombination can be detected by PCR amplification. When recombination is initiated in a strain carrying the MATa-stk T-->A base pair substitution mutation located 8 bp to the right of the HO endonuclease cleavage site, the stk mutation is frequently included in heteroduplex DNA formed between MAT and HML and undergoes mismatch correction. We have followed the kinetics of mismatch repair of the stk mutation by determining the DNA sequence of the PCR-amplified early intermediates of recombination. Mismatch correction of heteroduplex DNA is quite rapid (t1/2 = 6-10 min) compared to the 60 min required to complete repair of the double-strand break. Mismatch repair occurs soon after the 3'-ended MAT-stk strand invades HML and forms heteroduplex DNA. Moreover, nearly all the correction events are restorations, in which the invading MAT-stk strand is corrected to the genotype of the resident HML donor. This rapid restoration ensures that the net result will be a gene conversion at the MAT locus. Rapid and preferential mismatch repair of heteroduplex DNA has important implications in understanding meiotic recombination. Images Fig. 3 Fig. 4

Haber, J E; Ray, B L; Kolb, J M; White, C I

1993-01-01

129

Mating type-specific cell-cell recognition of Saccharomyces cerevisiae: cell wall attachment and active sites of a- and alpha-agglutinin.  

PubMed Central

Mating type-specific agglutination of Saccharomyces cerevisiae a and alpha cells depends on the heterophilic interaction of two cell surface glycoproteins, the gene products of AG alpha 1 and AGA2. Evidence is presented with immunogold labelling that the alpha-agglutinin is part of the outer fimbrial cell wall coat. The a-agglutinin is bound via two S-S bridges (Cys7 and Cys50) to a cell wall component, most probably the gene product of AGA1. His273 of alpha-agglutinin has previously been shown to be essential for a- and alpha-agglutinin interaction and a model based on two opposing ion-pairs had been proposed. By site-directed mutagenesis this possibility has now been excluded. With the help of various peptides, either chemically synthesized, obtained by proteolysis of intact glycosylated a-agglutinin or prepared from a fusion protein expressed in Escherichia coli, the biologically active region of a-agglutinin was located at the C-terminus of the molecule. A peptide consisting of the C-terminal 10 amino acids (GSPIN-TQYVF) was active in nanomolar concentrations. Saccharide moieties, therefore, are not essential for the mating type-specific cell-cell interaction; glycosylated peptides are, however, four to five times more active than non-glycosylated ones. Comparisons of the recognition sequences of the S. cerevisiae agglutinins with that of the Dictyostelium contact site A glycoprotein (gp80), as well as with those of the various families of cell adhesion molecules of higher eucaryotes, have been made and are discussed. Images

Cappellaro, C; Baldermann, C; Rachel, R; Tanner, W

1994-01-01

130

Mating type-specific cell-cell recognition of Saccharomyces cerevisiae: cell wall attachment and active sites of a- and alpha-agglutinin.  

PubMed

Mating type-specific agglutination of Saccharomyces cerevisiae a and alpha cells depends on the heterophilic interaction of two cell surface glycoproteins, the gene products of AG alpha 1 and AGA2. Evidence is presented with immunogold labelling that the alpha-agglutinin is part of the outer fimbrial cell wall coat. The a-agglutinin is bound via two S-S bridges (Cys7 and Cys50) to a cell wall component, most probably the gene product of AGA1. His273 of alpha-agglutinin has previously been shown to be essential for a- and alpha-agglutinin interaction and a model based on two opposing ion-pairs had been proposed. By site-directed mutagenesis this possibility has now been excluded. With the help of various peptides, either chemically synthesized, obtained by proteolysis of intact glycosylated a-agglutinin or prepared from a fusion protein expressed in Escherichia coli, the biologically active region of a-agglutinin was located at the C-terminus of the molecule. A peptide consisting of the C-terminal 10 amino acids (GSPIN-TQYVF) was active in nanomolar concentrations. Saccharide moieties, therefore, are not essential for the mating type-specific cell-cell interaction; glycosylated peptides are, however, four to five times more active than non-glycosylated ones. Comparisons of the recognition sequences of the S. cerevisiae agglutinins with that of the Dictyostelium contact site A glycoprotein (gp80), as well as with those of the various families of cell adhesion molecules of higher eucaryotes, have been made and are discussed. PMID:7957044

Cappellaro, C; Baldermann, C; Rachel, R; Tanner, W

1994-10-17

131

A new yeast PUF family protein, Puf6p, represses ASH1 mRNA translation and is required for its localization  

PubMed Central

In yeast Saccharomyces cerevisiae, Ash1p, a protein determinant for mating-type switching, is segregated within the daughter cell nucleus to establish asymmetry of HO expression. The accumulation of Ash1p results from ASH1 mRNA that is sorted as a ribonucleoprotein particle (mRNP or locasome) to the distal tip of the bud where translation occurs. To study the mechanism regulating ASH1 mRNA translation, we isolated the ASH1 locasome and characterized the associated proteins by MALDI-TOF. One of these proteins was Puf6p, a new member of the PUF family of highly conserved RNA-binding proteins such as Pumilio in Drosophila, responsible for translational repression, usually to effect asymmetric expression. Puf6p-bound PUF consensus sequences in the 3?UTR of ASH1 mRNA and repressed the translation of ASH1 mRNA both in vivo and in vitro. In the puf6? strain, asymmetric localization of both Ash1p and ASH1 mRNA were significantly reduced. We propose that Puf6p is a protein that functions in the translational control of ASH1 mRNA, and this translational inhibition is necessary before localization can proceed.

Gu, Wei; Deng, Yingfeng; Zenklusen, Daniel; Singer, Robert H.

2004-01-01

132

Mating Type Gene Homologues and Putative Sex Pheromone-Sensing Pathway in Arbuscular Mycorrhizal Fungi, a Presumably Asexual Plant Root Symbiont  

PubMed Central

The fungal kingdom displays a fascinating diversity of sex-determination systems. Recent advances in genomics provide insights into the molecular mechanisms of sex, mating type determination, and evolution of sexual reproduction in many fungal species in both ancient and modern phylogenetic lineages. All major fungal groups have evolved sexual differentiation and recombination pathways. However, sexuality is unknown in arbuscular mycorrhizal fungi (AMF) of the phylum Glomeromycota, an ecologically vital group of obligate plant root symbionts. AMF are commonly considered an ancient asexual lineage dating back to the Ordovician, approximately 460 M years ago. In this study, we used genomic and transcriptomic surveys of several AMF species to demonstrate the presence of conserved putative sex pheromone-sensing mitogen-activated protein (MAP) kinases, comparable to those described in Ascomycota and Basidiomycota. We also find genes for high mobility group (HMG) transcription factors, homologous to SexM and SexP genes in the Mucorales. The SexM genes show a remarkable sequence diversity among multiple copies in the genome, while only a single SexP sequence was detected in some isolates of Rhizophagus irregularis. In the Mucorales and Microsporidia, the sexM gene is flanked by genes for a triosephosphate transporter (TPT) and a RNA helicase, but we find no evidence for synteny in the vicinity of the Sex locus in AMF. Nonetheless, our results, together with previous observations on meiotic machinery, suggest that AMF could undergo a complete sexual reproduction cycle.

Halary, Sebastien; Daubois, Laurence; Terrat, Yves; Ellenberger, Sabrina; Wostemeyer, Johannes; Hijri, Mohamed

2013-01-01

133

Phylogenetic relationships between members of the crucifer pathogenic Leptosphaeria maculans species complex as shown by mating type (MAT1-2), actin, and beta-tubulin sequences.  

PubMed

The dothideomycetous fungus Leptosphaeria maculans comprises a complex of species differing in specificity and pathogenicity on Brassica napus. Twenty-eight isolates were investigated and compared to 20 other species of the Pleosporales order. Sequences of the mating type MAT1-2 (23), fragments of actin (48) and beta-tubulin (45) genes were determined and used for phylogenetic analyses inferred by maximum parsimony, distance, maximum likelihood, and Bayesian approaches. These different approaches using single genes essentially confirmed findings using concatanated sequences. L. maculans formed a monophyletic group separate from Leptosphaeria biglobosa. The L. biglobosa clade encompasses five sub-clades; this finding is consistent with classification made previously on the basis of internal-transcribed sequences of the ribosomal DNA repeat. The propensity for purifying and neutral evolution of the three genes was determined using sliding window analysis, a technique not previously applied to genes of filamentous fungi. For members of the L. maculans species complex, this approach showed that in comparison to actin and beta-tubulin, exonic sequences of MAT1-2 were more diverse and appeared to evolve at a faster rate. However, different regions of MAT1-2 displayed different degrees of sequence conservation. The more conserved upstream region (including the High Mobility Group domain) may be better suited for interspecies differentiation, while the more diverse downstream region is more appropriate for intraspecies comparisons. PMID:16122948

Voigt, Kerstin; Cozijnsen, Anton J; Kroymann, Jürgen; Pöggeler, Stefanie; Howlett, Barbara J

2005-11-01

134

Transcriptional regulation at the yeast nuclear envelope  

PubMed Central

The spatial organization of the genome inside the nucleus affects many nuclear processes, such as DNA replication, DNA repair, and gene transcription. In metazoans, the nuclear periphery harbors mainly repressed genes that associate with the nuclear lamina. This review discusses how peripheral positioning is connected to transcriptional regulation in yeasts. Tethering of reporter genes to the nuclear envelope was found to result in transcriptional silencing. Similarly, repression of the silent mating type loci and subtelomeric genes is influenced by their position close to the nuclear envelope. In contrast, active genes are bound by nucleoporins and inducible genes associate with the nuclear pore complex upon activation. Taken together, these results portray the nuclear envelope as a platform for transcriptional regulation, both through activation at nuclear pores and silencing at the nuclear envelope.

Steglich, Babett; Sazer, Shelley; Ekwall, Karl

2013-01-01

135

Mating types in screwworm populations  

SciTech Connect

Response is given to questions raised by L.E. LaChance, et al., regarding the types of screwworm that occur in Mexico and anatomical differences in male genitalia among types. Errors in chromosome length and arm ratios are discussed. Results of testing the V-81 strain (sterile males) indicate that mating barriers exist even at high release rates. Mating discrimination must be high for a population to withstand an excess of sterile flies. The relevance of this to eradication programs is discussed. (RJC)

Richardson, R.H.; Ellison, J.R.; Averhoff, W.W.

1982-12-10

136

H3K9me-Independent Gene Silencing in Fission Yeast Heterochromatin by Clr5 and Histone Deacetylases  

PubMed Central

Nucleosomes in heterochromatic regions bear histone modifications that distinguish them from euchromatic nucleosomes. Among those, histone H3 lysine 9 methylation (H3K9me) and hypoacetylation have been evolutionarily conserved and are found in both multicellular eukaryotes and single-cell model organisms such as fission yeast. In spite of numerous studies, the relative contributions of the various heterochromatic histone marks to the properties of heterochromatin remain largely undefined. Here, we report that silencing of the fission yeast mating-type cassettes, which are located in a well-characterized heterochromatic region, is hardly affected in cells lacking the H3K9 methyltransferase Clr4. We document the existence of a pathway parallel to H3K9me ensuring gene repression in the absence of Clr4 and identify a silencing factor central to this pathway, Clr5. We find that Clr5 controls gene expression at multiple chromosomal locations in addition to affecting the mating-type region. The histone deacetylase Clr6 acts in the same pathway as Clr5, at least for its effects in the mating-type region, and on a subset of other targets, notably a region recently found to be prone to neo-centromere formation. The genomic targets of Clr5 also include Ste11, a master regulator of sexual differentiation. Hence Clr5, like the multi-functional Atf1 transcription factor which also modulates chromatin structure in the mating-type region, controls sexual differentiation and genome integrity at several levels. Globally, our results point to histone deacetylases as prominent repressors of gene expression in fission yeast heterochromatin. These deacetylases can act in concert with, or independently of, the widely studied H3K9me mark to influence gene silencing at heterochromatic loci.

Hansen, Klavs R.; Hazan, Idit; Shanker, Sreenath; Watt, Stephen; Verhein-Hansen, Janne; Bahler, Jurg; Martienssen, Robert A.; Partridge, Janet F.; Cohen, Amikam; Thon, Genevieve

2011-01-01

137

Genomes of Ashbya fungi isolated from insects reveal four mating-type loci, numerous translocations, lack of transposons, and distinct gene duplications.  

PubMed

The filamentous fungus Ashbya gossypii is a cotton pathogen transmitted by insects. It is readily grown and manipulated in the laboratory and is commercially exploited as a natural overproducer of vitamin B2. Our previous genome analysis of A. gossypii isolate ATCC10895, collected in Trinidad nearly 100 years ago, revealed extensive synteny with the Saccharomyces cerevisiae genome, leading us to use it as a model organism to understand the evolution of filamentous growth. To further develop Ashbya as a model system, we have investigated the ecological niche of A. gossypii and isolated additional strains and a sibling species, both useful in comparative analysis. We isolated fungi morphologically similar to A. gossypii from different plant-feeding insects of the suborder Heteroptera, generated a phylogenetic tree based on rDNA-ITS sequences, and performed high coverage short read sequencing with one A. gossypii isolate from Florida, a new species, Ashbya aceri, isolated in North Carolina, and a genetically marked derivative of ATCC10895 intensively used for functional studies. In contrast to S. cerevisiae, all strains carry four not three mating type loci, adding a new puzzle in the evolution of Ashbya species. Another surprise was the genome identity of 99.9% between the Florida strain and ATCC10895, isolated in Trinidad. The A. aceri and A. gossypii genomes show conserved gene orders rearranged by eight translocations, 90% overall sequence identity, and fewer tandem duplications in the A. aceri genome. Both species lack transposable elements. Finally, our work identifies plant-feeding insects of the suborder Heteroptera as the most likely natural reservoir of Ashbya, and that infection of cotton and other plants may be incidental to the growth of the fungus in its insect host. PMID:23749448

Dietrich, Fred S; Voegeli, Sylvia; Kuo, Sidney; Philippsen, Peter

2013-08-01

138

Genomes of Ashbya Fungi Isolated from Insects Reveal Four Mating-Type Loci, Numerous Translocations, Lack of Transposons, and Distinct Gene Duplications  

PubMed Central

The filamentous fungus Ashbya gossypii is a cotton pathogen transmitted by insects. It is readily grown and manipulated in the laboratory and is commercially exploited as a natural overproducer of vitamin B2. Our previous genome analysis of A. gossypii isolate ATCC10895, collected in Trinidad nearly 100 years ago, revealed extensive synteny with the Saccharomyces cerevisiae genome, leading us to use it as a model organism to understand the evolution of filamentous growth. To further develop Ashbya as a model system, we have investigated the ecological niche of A. gossypii and isolated additional strains and a sibling species, both useful in comparative analysis. We isolated fungi morphologically similar to A. gossypii from different plant-feeding insects of the suborder Heteroptera, generated a phylogenetic tree based on rDNA-ITS sequences, and performed high coverage short read sequencing with one A. gossypii isolate from Florida, a new species, Ashbya aceri, isolated in North Carolina, and a genetically marked derivative of ATCC10895 intensively used for functional studies. In contrast to S. cerevisiae, all strains carry four not three mating type loci, adding a new puzzle in the evolution of Ashbya species. Another surprise was the genome identity of 99.9% between the Florida strain and ATCC10895, isolated in Trinidad. The A. aceri and A. gossypii genomes show conserved gene orders rearranged by eight translocations, 90% overall sequence identity, and fewer tandem duplications in the A. aceri genome. Both species lack transposable elements. Finally, our work identifies plant-feeding insects of the suborder Heteroptera as the most likely natural reservoir of Ashbya, and that infection of cotton and other plants may be incidental to the growth of the fungus in its insect host.

Dietrich, Fred S.; Voegeli, Sylvia; Kuo, Sidney; Philippsen, Peter

2013-01-01

139

Red yeast  

MedlinePLUS

... with this combination.Talk with your health provider.Cyclosporine (Neoral, Sandimmune)Red yeast might affect the muscles. Cyclosporine (Neoral, Sandimmune) might also affect the muscles. Taking ...

140

Yeast Infections  

MedlinePLUS

Candida is the scientific name for yeast. It is a fungus that lives almost everywhere, including in ... infection that causes white patches in your mouth Candida esophagitis is thrush that spreads to your esophagus, ...

141

Counting Yeast.  

ERIC Educational Resources Information Center

Describes changes to a traditional study of population in yeast colonies. Changes to the procedures include: (1) only one culture per student team; (2) cultures are inoculated only once; and (3) the same tube is sampled daily. (DDR)

Bealer, Jonathan; Welton, Briana

1998-01-01

142

Electric Switches  

NSDL National Science Digital Library

In this activity, learners incorporate a simple switch into a battery/bulb circuit. Learners will use their knowledge of circuits to design and make their own switches using common materials. Learners will also identify switches found in common appliances. Note: This activity is designed to be done under the supervision of an educator familiar with electrical and electronic concepts.

Ieee

2013-07-08

143

Three evolutionary lineages of tomato wilt pathogen, Fusarium oxysporum f. sp. lycopersici , based on sequences of IGS, MAT1 , and pg1 , are each composed of isolates of a single mating type and a single or closely related vegetative compatibility group  

Microsoft Academic Search

Three evolutionary lineages of the tomato wilt pathogen Fusarium oxysporum f. sp. lycopersici were found among a worldwide sample of isolates based on phylogenetic analysis of the ribosomal DNA intergenic spacer region. Each lineage consisted of isolates mainly belonging to a single or closely related vegetative compatibility group (VCG) and a single mating type (MAT). The first lineage (A1) was

Masato Kawabe; Yumiko Kobayashi; Gen Okada; Isamu Yamaguchi; Tohru Teraoka; Tsutomu Arie

2005-01-01

144

Ethernet Switching  

NSDL National Science Digital Library

Created by Tony Castro of the Information and Communications Technologies Center (ICT), this simulation demonstrates ethernet switching. The animation depicts three separate local area networks connecting to an ethernet hub. The animation also includes descriptive text. This resource would be a helpful addition to any course on information and communications technologies as it allows students to see exactly how ethernet switching works.

Castro, Tony

2012-10-25

145

Switching Amplifiers  

NSDL National Science Digital Library

Created by Work-Ready Electronics, a project of the Advanced Technological Education, this module walks visitors through switching amplifiers. The site content is divided up into four sections: Switching Amplifiers Introduction, Class D Switching Amplifiers, Switching RF Power Amplifiers, and Troubleshooting. There is a quiz for each section to test what students learned in the module in the Knowledge Probe section, and the Learning Resources section contains four activities to help cement student understanding. There are also further resources - both print and Web based - for more information and two Questor games, a Flash quiz that reiterates the material covered. The Notebook function allows visitors to take notes and review them at any time. This is an excellent resource students and educators in electronics technician programs to introduce and explore switching amplifiers.

2008-09-04

146

Clavispora opuntiae and other yeasts associated with the moth Sigelgaita sp. in the cactus Pilosocereus arrabidae of Rio de Janeiro, Brazil.  

PubMed

Clavispora opuntiae was the prevalent yeast associated with the feeding sites of Sigelgaita sp. larvae in the cactus Pilosocereus arrabidae. Also associated with this habitat were Candida sonorensis, Pichia cactophila, Pichia barkeri, Candida sp. A, Geotrichum sp., Geotrichum sericeum and the yeast like organisms Prototheca zopfii and Acremonium sp. Atypical yeast biotypes that may represent new species of Pichia, Sporopachydermia and Candida were isolated. Mating types of Clavispora opuntiae were at a ratio 70 h- to 3 h- and reduced levels of sporulation suggested low pressure for sexual reproduction in this habitat. Sigelgaita sp. probably was not an important vector for Clavispora opuntiae because it was not isolated from an adult or eggs of this moth. PMID:1285643

Rosa, C A; Hagler, A N; Mendonça-Hagler, L C; de Morais, P B; Gomes, C M; Monteiro, R F

1992-11-01

147

Gene Switches  

NSDL National Science Digital Library

In this activity, learners explore how genetic switches function and the role of genetic switches in the process of evolution. To make these concepts less abstract and more understandable, learners first view a series of video clips and animations from the HHMI DVD (or online) "Evolution: Constant Change and Common Threads." Then, learners construct a model of a gene switch using craft materials or FridgiGears (magnetic gears). This activity can be done as a demonstration, a student inquiry activity, or a combination of the two.

Colvard, Mary

2010-01-01

148

Ras Signaling in Yeast  

PubMed Central

Since the study of yeast RAS and adenylate cyclase in the early 1980s, yeasts including budding and fission yeasts contributed significantly to the study of Ras signaling. First, yeast studies provided insights into how Ras activates downstream signaling pathways. Second, yeast studies contributed to the identification and characterization of GAP and GEF proteins, key regulators of Ras. Finally, the study of yeast provided many important insights into the understanding of C-terminal processing and membrane association of Ras proteins.

Tamanoi, Fuyuhiko

2011-01-01

149

Genetic structure of Kurtzmaniella cleridarum, a cactus flower beetle yeast of the Sonoran and Mojave Deserts: speciation by distance?  

PubMed

We studied 95 isolates of the yeast species Kurtzmaniella cleridarum recovered from nitidulid beetles collected in flowers of cacti of the Sonoran Desert of southern Arizona and the Mojave Desert of California. They were characterized on the basis of mating type and ten polymorphic DNA markers in relation to their geographic distribution. Although all loci appeared to be free of strong linkage, the recovered haplotypes represented but a small fraction of possible combinations, indicating that abundant asexual reproduction of local genotypes accounts for much of population growth, even though the yeast is capable of sexual recombination in nature. Much of the genetic differentiation took place at the local level, indicating that gene flow across the various localities is limited. However, a relationship exists between overall genetic differentiation and geography over long distances. We estimated that populations separated by c. 1300 km would share no alleles in common and that such a separation might be enough to favor the onset of speciation. PMID:23865628

Lachance, Marc-André; Perri, Ami M; Farahbakhsh, Amy S; Starmer, William T

2013-11-01

150

Modeling diauxic glycolytic oscillations in yeast.  

PubMed

Glycolytic oscillations in a stirred suspension of starved yeast cells is an excellent model system for studying the dynamics of metabolic switching in living systems. In an open-flow system the oscillations can be maintained indefinitely at a constant operating point where they can be characterized quantitatively by experimental quenching and bifurcation analysis. In this article, we use these methods to show that the dynamics of oscillations in a closed system is a simple transient version of the open-system dynamics. Thus, easy-setup closed-system experiments are also useful for investigations of central metabolism dynamics of yeast cells. We have previously proposed a model for the open system comprised of the primary fermentative reactions in yeast that quantitatively describes the oscillatory dynamics. However, this model fails to describe the transient behavior of metabolic switching in a closed-system experiment by feeding the yeast suspension with a glucose pulse-notably the initial NADH spike and final NADH rise. Another object of this study is to gain insight into the secondary low-flux metabolic pathways by feeding starved yeast cells with various metabolites. Experimental and computational results strongly suggest that regulation of acetaldehyde explains the observed behavior. We have extended the original model with regulation of pyruvate decarboxylase, a reversible alcohol dehydrogenase, and drainage of pyruvate. Using the method of time rescaling in the extended model, the description of the transient closed-system experiments is significantly improved. PMID:21081066

Hald, Bjørn Olav; Sørensen, Preben G

2010-11-17

151

Modeling Diauxic Glycolytic Oscillations in Yeast  

PubMed Central

Glycolytic oscillations in a stirred suspension of starved yeast cells is an excellent model system for studying the dynamics of metabolic switching in living systems. In an open-flow system the oscillations can be maintained indefinitely at a constant operating point where they can be characterized quantitatively by experimental quenching and bifurcation analysis. In this article, we use these methods to show that the dynamics of oscillations in a closed system is a simple transient version of the open-system dynamics. Thus, easy-setup closed-system experiments are also useful for investigations of central metabolism dynamics of yeast cells. We have previously proposed a model for the open system comprised of the primary fermentative reactions in yeast that quantitatively describes the oscillatory dynamics. However, this model fails to describe the transient behavior of metabolic switching in a closed-system experiment by feeding the yeast suspension with a glucose pulse—notably the initial NADH spike and final NADH rise. Another object of this study is to gain insight into the secondary low-flux metabolic pathways by feeding starved yeast cells with various metabolites. Experimental and computational results strongly suggest that regulation of acetaldehyde explains the observed behavior. We have extended the original model with regulation of pyruvate decarboxylase, a reversible alcohol dehydrogenase, and drainage of pyruvate. Using the method of time rescaling in the extended model, the description of the transient closed-system experiments is significantly improved.

Hald, Bj?rn Olav; S?rensen, Preben G.

2010-01-01

152

Reinventing Heterochromatin in Budding Yeasts: Sir2 and the Origin Recognition Complex Take Center Stage ?  

PubMed Central

The transcriptional silencing of the cryptic mating-type loci in Saccharomyces cerevisiae is one of the best-studied models of repressive heterochromatin. However, this type of heterochromatin, which is mediated by the Sir proteins, has a distinct molecular composition compared to the more ubiquitous type of heterochromatin found in Schizosaccharomyces pombe, other fungi, animals, and plants and characterized by the presence of HP1 (heterochromatin protein 1). This review discusses how the loss of important heterochromatin proteins, including HP1, in the budding yeast lineage presented an evolutionary opportunity for the development and diversification of alternative varieties of heterochromatin, in which the conserved deacetylase Sir2 and the replication protein Orc1 play key roles. In addition, we highlight how this diversification has been facilitated by gene duplications and has contributed to adaptations in lifestyle.

Hickman, Meleah A.; Froyd, Cara A.; Rusche, Laura N.

2011-01-01

153

Optical switch  

DOEpatents

An optical switching device (10) is provided whereby light from a first glass fiber (16) or a second glass fiber (14) may be selectively transmitted into a third glass fiber (18). Each glass fiber is provided with a focusing and collimating lens system (26, 28, 30). In one mode of operation, light from the first glass fiber (16) is reflected by a planar mirror (36) into the third glass fiber (18). In another mode of operation, light from the second glass fiber (14) passes directly into the third glass fiber (18). The planar mirror (36) is attached to a rotatable table (32) which is rotated to provide the optical switching.

Reedy, Robert P. (Livermore, CA) [Livermore, CA

1987-01-01

154

Optical switch  

DOEpatents

An optical switching device is provided whereby light from a first glass fiber or a second glass fiber may be selectively transmitted into a third glass fiber. Each glass fiber is provided with a focusing and collimating lens system. In one mode of operation, light from the first glass fiber is reflected by a planar mirror into the third glass fiber. In another mode of operation, light from the second glass fiber passes directly into the third glass fiber. The planar mirror is attached to a rotatable table which is rotated to provide the optical switching. 3 figs.

Reedy, R.P.

1987-11-10

155

Evidence for maintenance of sex determinants but not of sexual stages in red yeasts, a group of early diverged basidiomycetes  

PubMed Central

Background The red yeasts are an early diverged group of basidiomycetes comprising sexual and asexual species. Sexuality is based on two compatible mating types and sexual identity is determined by MAT loci that encode homeodomain transcription factors, peptide pheromones and their receptors. The objective of the present study was to investigate the presence and integrity of MAT genes throughout the phylogenetic diversity of red yeasts belonging to the order Sporidiobolales. Results We surveyed 18 sexual heterothallic and self-fertile species and 16 asexual species. Functional pheromone receptor homologues (STE3.A1 and STE3.A2) were found in multiple isolates of most of the sexual and asexual species. For each of the two mating types, sequence comparisons with whole-genome data indicated that synteny tended to be conserved along the pheromone receptor region. For the homeodomain transcription factor, likelihood methods suggested that diversifying selection acting on the self/non-self recognition region promotes diversity in sexual species, while rapid evolution seems to be due to relaxed selection in asexual strains. Conclusions The majority of both sexual and asexual species of red yeasts have functional pheromone receptors and homeodomain homologues. This and the frequent existence of asexual strains within sexual species, makes the separation between sexual and asexual species imprecise. Events of loss of sexuality seem to be recent and frequent, but not uniformly distributed within the Sporidiobolales. Loss of sex could promote speciation by fostering the emergence of asexual lineages from an ancestral sexual stock, but does not seem to contribute to the generation of exclusively asexual lineages that persist for a long time.

2011-01-01

156

Cloning of a novel constitutively expressed pectate lyase gene pelB from Fusarium solani f. sp. pisi (Nectria haematococca, mating type VI) and characterization of the gene product expressed in Pichia pastoris.  

PubMed Central

Since plant-pathogenic fungi must penetrate through pectinaceous layers of the host cell wall, pectin-degrading enzymes are thought to be important for pathogenesis. Antibodies prepared against a pectin-inducible pectate lyase (pectate lyase A [PLA]) produced by a phytopathogenic fungus, Fusarium solani f. sp. pisi (Nectria haematococca, mating type VI), was previously found to protect the host from infection. The gene (pelA) and its cDNA were cloned and sequenced. Here we report the isolation of a new pectate lyase gene, pelB, from a genomic library of F. solani f. sp. pisi with the pelA cDNA as the probe. A 2.6-kb DNA fragment containing pelB and its flanking regions was sequenced. The coding region of pelB was amplified by reverse transcription-mediated PCR, using total RNA isolated from F. solani pisi culture grown in the presence of glucose as the sole carbon source. The predicted open reading frame of pelB would encode a 25.6-kDa protein of 244 amino acids which has 65% amino acid sequence identity with PLA from F. solani f. sp. pisi but no significant homology with other pectinolytic enzymes. The first 16 amino acid residues at the N terminus appeared to be a signal peptide. The pelB cDNA was expressed in Pichia pastoris, yielding a pectate lyase B (PLB) which was found to be a glycoprotein of 29 kDa. PLB was purified to homogeneity by using a two-step procedure involving ammonium sulfate precipitation followed by Superdex G75 gel filtration chromatography. Purified PLB showed optimal lyase activity at pH 10.0. A rapid drop in the viscosity of the substrate and Mono Q anion-exchange chromatography of the products generated by the lyase showed that PLB cleaved polygalacturonate chains in an endo fashion. Western blotting (immunoblotting) with antibodies raised against PLA showed that PLB and PLA are immunologically related to each other. The 5' flanking regions of both pelA and pelB were translationally fused to the beta-glucuronidase gene and introduced into F. solani f. sp. pisi, and beta-glucuronidase activities of the transformants were measured. Expression of the marker gene by the transformants showed that pelA expression is induced by pectin and repressed by glucose, whereas expression of pelB is constitutive and is not subject to glucose repression. Reverse transcription-mediated PCR showed that both pelA and pelB are expressed when F. solani f. sp. pisi infects pea epicotyl.

Guo, W; Gonzalez-Candelas, L; Kolattukudy, P E

1995-01-01

157

Yeast Infection (Candidiasis)  

MedlinePLUS

... for adults A A A This is a candida (yeast) infection of the skin folds of the ... infection with the common yeast (or fungus) organism, Candida albicans, which is commonly found in the environment. ...

158

Phenoptosis in yeasts.  

PubMed

The current view on phenoptosis and apoptosis as genetic programs aimed at eliminating potentially dangerous organisms and cells, respectively, is given. Special emphasis is placed on apoptosis (phenoptosis) in yeasts: intracellular defects and a plethora of external stimuli inducing apoptosis in yeasts; distinctive morphological and biochemical hallmarks accompanying apoptosis in yeasts; pro- and antiapoptotic factors involved in yeast apoptosis signaling; consecutive stages of apoptosis from external stimulus to the cell death; a prominent role of mitochondria and other organelles in yeast apoptosis; possible pathways for release of apoptotic factors from the intermembrane mitochondrial space into the cytosol are described. Using some concrete examples, the obvious physiological importance and expediency of altruistic death of yeast cells is shown. Poorly known aspects of yeast apoptosis and prospects for yeast apoptosis study are defined. PMID:22817540

Sukhanova, E I; Rogov, A G; Severin, F F; Zvyagilskaya, R A

2012-07-01

159

Yeast Based Sensors  

NASA Astrophysics Data System (ADS)

Since the first microbial cell sensor was studied by Karube et al. in 1977, many types of yeast based sensors have been developed as analytical tools. Yeasts are known as facultative anaerobes. Facultative anaerobes can survive in both aerobic and anaerobic conditions. The yeast based sensor consisted of a DO electrode and an immobilized omnivorous yeast. In yeast based sensor development, many kinds of yeast have been employed by applying their characteristics to adapt to the analyte. For example, Trichosporon cutaneum was used to estimate organic pollution in industrial wastewater. Yeast based sensors are suitable for online control of biochemical processes and for environmental monitoring. In this review, principles and applications of yeast based sensors are summarized.

Shimomura-Shimizu, Mifumi; Karube, Isao

160

Reset Switching Probability of Resistive Switching Devices  

Microsoft Academic Search

The reset switching probability of resistive switching devices is characterized in array testing. The measured switching probability can be quantitatively explained based on the mecha- nism of a thermally activated reset process. An analytical model of switching probability is developed to describe the dependence of reset probability on operation parameters, including applied voltage, selection transistor gate voltage, and pulsewidth. The

An Chen; Ming-Ren Lin

2011-01-01

161

Central Roles of Small GTPases in the Development of Cell Polarity in Yeast and Beyond  

PubMed Central

Summary: The establishment of cell polarity is critical for the development of many organisms and for the function of many cell types. A large number of studies of diverse organisms from yeast to humans indicate that the conserved, small-molecular-weight GTPases function as key signaling proteins involved in cell polarization. The budding yeast Saccharomyces cerevisiae is a particularly attractive model because it displays pronounced cell polarity in response to intracellular and extracellular cues. Cells of S. cerevisiae undergo polarized growth during various phases of their life cycle, such as during vegetative growth, mating between haploid cells of opposite mating types, and filamentous growth upon deprivation of nutrition such as nitrogen. Substantial progress has been made in deciphering the molecular basis of cell polarity in budding yeast. In particular, it becomes increasingly clear how small GTPases regulate polarized cytoskeletal organization, cell wall assembly, and exocytosis at the molecular level and how these GTPases are regulated. In this review, we discuss the key signaling pathways that regulate cell polarization during the mitotic cell cycle and during mating.

Park, Hay-Oak; Bi, Erfei

2007-01-01

162

Lager brewing yeast  

Microsoft Academic Search

Lager brewing yeast is a group of closely related strains of Saccharomyces pastorianus\\/S. carlsbergensis used for lager beer production all over the world, making it one of the most important industrial yeasts. The pure cultivation\\u000a of yeast was established in the early 1880’s with immediate practical success for lager brewing yeast. However, almost a century\\u000a would elapse before its genetics

Yukiko Kodama; Morten C. Kielland-Brandt; Jørgen Hansen

163

Xylose fermentation by yeasts  

Microsoft Academic Search

Utilization and fermentation of xylose by the yeasts Pachysolen tannophilus I fGB 0101 and Pichia stipitis 5773 to 5776 under aerobic and anaerobic conditions are investigated. Pa. tannophilus requires biotin and thiamine for growth, whereas Pi. stipitis does not, and growth of both yeasts is stimulated by yeast extract. Pi. stipitis converts xylose (30 g\\/l) to ethanol under anaerobic conditions

H. Dellweg; M. Rizzi; H. Methner; D. Debus

1984-01-01

164

Cohabitation of insulators and silencing elements in yeast subtelomeric regions.  

PubMed Central

In budding yeast, the telomeric DNA is flanked by a combination of two subtelomeric repetitive sequences, the X and Y' elements. We have investigated the influence of these sequences on telomeric silencing. The telomere-proximal portion of either X or Y' dampened silencing when located between the telomere and the reporter gene. These elements were named STARs, for subtelomeric anti-silencing regions. STARs can also counteract silencer-driven repression at the mating-type HML locus. When two STARs bracket a reporter gene, its expression is no longer influenced by surrounding silencing elements, although these are still active on a second reporter gene. In addition, an intervening STAR uncouples the silencing of neighboring genes. STARs thus display the hallmarks of insulators. Protection from silencing is recapitulated by multimerized oligonucleotides representing Tbf1p- and Reb1p-binding sites, as found in STARs. In contrast, sequences located more centromere proximal in X and Y' elements reinforce silencing. They can promote silencing downstream of an insulated expressed domain. Overall, our results suggest that the silencing emanating from telomeres can be propagated in a discontinuous manner via a series of subtelomeric relay elements.

Fourel, G; Revardel, E; Koering, C E; Gilson, E

1999-01-01

165

Heterologous Protein Secretion from Yeast  

Microsoft Academic Search

Secretion of calf prochymosin from yeast yields fully activable zymogen while production in the yeast cytoplasm yields insoluble, unactivable enzyme with aberrant disulfide bonding. Factors that increase the efficiency of secretion of prochymosin from yeast are use of a yeast secretion signal sequence, integration of the transcriptional unit into the yeast genome, and specific mutations in a number of host

Robert A. Smith; Margaret J. Duncan; Donald T. Moir

1985-01-01

166

Population Growth in Yeasts  

NSDL National Science Digital Library

This lesson is the second of two that explore cellular respiration and population growth in yeasts. In the first lesson, students set up a simple way to indirectly observe and quantify the amount of respiration occurring in yeast-molasses cultures. Based on questions that arose during the first lesson and its associated activity, in this lesson students work in small groups to design experiments that will determine how environmental factors affect yeast population growth.

Engineering K-Ph.d. Program

167

High-Frequency Switching of Colony Morphology in Candida albicans  

Microsoft Academic Search

The pathogenic yeast Candida albicans switches heritably and at high frequency between at least seven general phenotypes identified by colony morphology on agar. Spontaneous conversion from the original smooth to variant phenotypes (star, ring, irregular wrinkle, hat, stipple, and fuzzy) occurs at a combined frequency of 1.4 × 10-4, but is increased 200 times by a low dose of ultraviolet

Bernice Slutsky; Jeffrey Buffo; David R. Soll

1985-01-01

168

Latching relay switch assembly  

DOEpatents

A latching relay switch assembly which includes a coil section and a switch or contact section. The coil section includes at least one permanent magnet and at least one electromagnet. The respective sections are, generally, arranged in separate locations or cavities in the assembly. The switch is latched by a permanent magnet assembly and selectively switched by an overriding electromagnetic assembly.

Duimstra, Frederick A. (Anaheim Hills, CA)

1991-01-01

169

Multiple Signaling Pathways Regulate Yeast Cell Death during the Response to Mating Pheromones  

PubMed Central

Mating pheromones promote cellular differentiation and fusion of yeast cells with those of the opposite mating type. In the absence of a suitable partner, high concentrations of mating pheromones induced rapid cell death in ?25% of the population of clonal cultures independent of cell age. Rapid cell death required Fig1, a transmembrane protein homologous to PMP-22/EMP/MP20/Claudin proteins, but did not require its Ca2+ influx activity. Rapid cell death also required cell wall degradation, which was inhibited in some surviving cells by the activation of a negative feedback loop involving the MAP kinase Slt2/Mpk1. Mutants lacking Slt2/Mpk1 or its upstream regulators also underwent a second slower wave of cell death that was independent of Fig1 and dependent on much lower concentrations of pheromones. A third wave of cell death that was independent of Fig1 and Slt2/Mpk1 was observed in mutants and conditions that eliminate calcineurin signaling. All three waves of cell death appeared independent of the caspase-like protein Mca1 and lacked certain “hallmarks” of apoptosis. Though all three waves of cell death were preceded by accumulation of reactive oxygen species, mitochondrial respiration was only required for the slowest wave in calcineurin-deficient cells. These findings suggest that yeast cells can die by necrosis-like mechanisms during the response to mating pheromones if essential response pathways are lacking or if mating is attempted in the absence of a partner.

Zhang, Nan-Nan; Dudgeon, Drew D.; Paliwal, Saurabh; Levchenko, Andre; Grote, Eric

2006-01-01

170

Metschnikowia proteae sp. nov., a nectarivorous insect-associated yeast species from Africa.  

PubMed

A collection of yeasts isolated from nectar of flowers of Protea caffra (Proteaceae) and associated scarab beetles (Atrichelaphinis tigrina, Cyrtothyrea marginalis, Trichostetha fascicularis and Heterochelus sp.) and drosophilid flies in South Africa, contained 28 isolates that could not be assigned to known species. Comparisons of the D1/D2 domains of the large subunit rRNA gene demonstrated the existence of three separate phylotypes with an affinity to the genus Metschnikowia and more specifically to the beetle-associated large-spored Metschnikowia clade. Twenty-six strains that had similar D1/D2 sequences were mixed in all pairwise combinations. They were found to mate and give rise to large asci typical of those in the clade. The name Metschnikowia proteae sp. nov. (type strain EBDT1Y1(T)?=?CBS 12522(T)?=?NRRL Y-48784(T); allotype strain EBDC2Y2?=?CBS 12521?=?NRRL Y-48785) is proposed to accommodate this novel species. The ecology of this novel yeast species is discussed in relation to its potential plant and insect host species. The additional two single strains isolated from Heterochelus sp. represent two novel undescribed species (Candida sp. 1 EBDM2Y3 and Candida sp. 2 EBDM8Y1). As these single strains are probably haploid mating types of Metschnikowia species, their description is deferred until the species are sufficiently well sampled to permit meaningful descriptions. PMID:22407789

de Vega, Clara; Guzmán, Beatriz; Lachance, Marc-André; Steenhuisen, Sandy-Lynn; Johnson, Steven D; Herrera, Carlos M

2012-10-01

171

Moonlighting Proteins in Yeasts  

PubMed Central

Proteins able to participate in unrelated biological processes have been grouped under the generic name of moonlighting proteins. Work with different yeast species has uncovered a great number of moonlighting proteins and shown their importance for adequate functioning of the yeast cell. Moonlighting activities in yeasts include such diverse functions as control of gene expression, organelle assembly, and modification of the activity of metabolic pathways. In this review, we consider several well-studied moonlighting proteins in different yeast species, paying attention to the experimental approaches used to identify them and the evidence that supports their participation in the unexpected function. Usually, moonlighting activities have been uncovered unexpectedly, and up to now, no satisfactory way to predict moonlighting activities has been found. Among the well-characterized moonlighting proteins in yeasts, enzymes from the glycolytic pathway appear to be prominent. For some cases, it is shown that despite close phylogenetic relationships, moonlighting activities are not necessarily conserved among yeast species. Organisms may utilize moonlighting to add a new layer of regulation to conventional regulatory networks. The existence of this type of proteins in yeasts should be taken into account when designing mutant screens or in attempts to model or modify yeast metabolism.

Gancedo, Carlos; Flores, Carmen-Lisset

2008-01-01

172

Light-regulated gene expression in yeast.  

PubMed

An important basic requirement of synthetic genetic networks is the option of external control of gene expression. Although several chemically inducible systems are available, all of these suffer from the common problem: the chemical inducers are difficult to remove so that to terminate the response. We have described a regulatory expression system for yeast, which employs light as inducer. This light switch translates light-controlled protein-protein interactions into the transcription of selected genes in a dose-dependent and reversible manner. PMID:22083743

Kozma-Bognar, Laszlo; Hajdu, Anita; Nagy, Ferenc

2012-01-01

173

Temporal switching jitter in photoconductive switches  

SciTech Connect

This paper reports on a recent comparison made between the Air Force Research Laboratory (AFRL) gallium arsenide, optically-triggered switch test configuration and the Sandia National Laboratories (SNL) gallium arsenide, optically-triggered switch test configuration. The purpose of these measurements was to compare the temporal switch jitter times. It is found that the optical trigger laser characteristics are dominant in determining the PCSS jitter.

GAUDET,JOHN A.; SKIPPER,MICHAEL C.; ABDALLA,MICHAEL D.; AHERN,SEAN M.; MAR,ALAN; LOUBRIEL,GUILLERMO M.; ZUTAVERN,FRED J.; O'MALLEY,MARTIN W.; HELGESON,WESLEY D.; ROMERO,SAMUEL P.

2000-04-13

174

RF MEMS switches and switch circuits  

Microsoft Academic Search

MEMS switches are devices that use mechanical movement to achieve a short circuit or an open circuit in the RF transmission line. RF MEMS switches are the specific micromechanical switches that are designed to operate at RF-to-millimeter-wave frequencies (0.1 to 100 GHz). The forces required for the mechanical movement can be obtained using electrostatic, magnetostatic, piezoelectric, or thermal designs. To

G. M. Rebeiz; J. B. Muldavin

2001-01-01

175

Characterization of Phenotypic Switching in Cryptococcus neoformans Biofilms  

PubMed Central

Cryptococcus neoformans is an encapsulated yeast-like fungus that is a relatively frequent cause of meningoencephalitis in immunocompromised patients and also occasionally causes disease in apparently healthy individuals. This fungus collectively forms biofilms on polystyrene plates and medical devices, whereas individually can undergo phenotypic switching. Both events have profound consequences in the establishment of fungal infection and are associated with persistent infection due to increase resistance to antimicrobial therapy. In this study, we characterized switch phenotypes in C. neoformans biofilms. Smooth, mucoid, and wrinkled switch phenotypes of various switching C. neoformans strains were examined for their adhering and biofilm-forming ability on 96-well plates using cell counts and 2,3-bis (2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino) carbonyl]-2H-tetrazolium hydroxide (XTT) reduction assay, respectively. Both assays showed that C. neoformans strains with the parent smooth phenotype adhered and formed stronger biofilms than their mucoid and wrinkled counterparts. Furthermore, the phenotypic switching frequencies of the individual colony types grown in biofilms or as planktonic cells were investigated. For the parent smooth variant of most strains, we found enhanced phenotypic switching in cryptococcal biofilms when compared to switching rates of planktonic cells. In contrast, the back-switching rate of mucoid to smooth variant was significantly higher in planktonic cells of seven strains of C. neoformans strains. These results suggested that phenotypic switching can occur in cryptococcal biofilms and extend our understanding of the relationship of both phenomena.

Martinez, Luis R.; Ibom, David C.; Casadevall, Arturo

2009-01-01

176

The DNA Damage Checkpoint Regulates a Transition between Yeast and Hyphal Growth in Schizosaccharomyces japonicus? †  

PubMed Central

Dimorphic yeasts change between unicellular growth and filamentous growth. Many dimorphic yeasts species are pathogenic for humans and plants, being infectious as invasive hypha. We have studied the determinants of the dimorphic switch in the nonpathogenic fission yeast Schizosaccharomyces japonicus, which is evolutionarily close to the well-characterized fission yeast S. pombe. We report that camptothecin, an inhibitor of topoisomerase I, reversibly induced the unicellular to hyphal transition in S. japonicus at low concentrations of camptothecin that did not induce checkpoint arrest and the transition required the DNA checkpoint kinase Chk1. Furthermore, a mutation of chk1 induced hyphal transition without camptothecin. Thus, we identify a second function for Chk1 distinct from its role in checkpoint arrest. Activation of the switch from single cell bipolar growth to monopolar filamentous growth may assist cells to evade the source of DNA damage.

Furuya, Kanji; Niki, Hironori

2010-01-01

177

RNAi in budding yeast  

PubMed Central

RNAi, a gene-silencing pathway triggered by double-stranded RNA, is conserved in diverse eukaryotic species but has been lost in the model budding yeast, Saccharomyces cerevisiae. Here, we show that RNAi is present in other budding-yeast species, including Saccharomyces castellii and Candida albicans. These species use noncanonical Dicer proteins to generate siRNAs, which mostly correspond to transposable elements and Y’ subtelomeric repeats. In S. castellii, RNAi mutants are viable but have excess Y’ mRNA levels. In S. cerevisiae, introducing Dicer and Argonaute of S. castellii restores RNAi, and the reconstituted pathway silences endogenous retrotransposons. These results identify a novel class of Dicer proteins, bring the tool of RNAi to the study of budding yeasts, and bring the tools of budding yeast to the study of RNAi.

Mower, Jeffrey P.; Wolfe, Kenneth H.; Fink, Gerald R.; Bartel, David P.

2013-01-01

178

Optical switching: Capillary action  

Microsoft Academic Search

Controlling light in optical systems quickly and easily is crucial for all-optical switching. An approach that does this by exploiting the condensation of gases in a porous structure could open up new avenues in the switching field.

Yuri Kivshar

2007-01-01

179

Yeast expression platforms  

Microsoft Academic Search

Yeasts provide attractive expression platforms. They combine ease of genetic manipulations and the option for a simple fermentation\\u000a design of a microbial organism with the capabilities of an eukaryotic organism to secrete and to modify a protein according\\u000a to a general eukaryotic scheme. For platform applications, a range of yeast species has been developed during the last decades.\\u000a We present

Erik Böer; Gerhard Steinborn; Gotthard Kunze; Gerd Gellissen

2007-01-01

180

On the mechanisms of glycolytic oscillations in yeast.  

PubMed

This work concerns the cause of glycolytic oscillations in yeast. We analyse experimental data as well as models in two distinct cases: the relaxation-like oscillations seen in yeast extracts, and the sinusoidal Hopf oscillations seen in intact yeast cells. In the case of yeast extracts, we use flux-change plots and model analyses to establish that the oscillations are driven by on/off switching of phosphofructokinase. In the case of intact yeast cells, we find that the instability leading to the appearance of oscillations is caused by the stoichiometry of the ATP-ADP-AMP system and the allosteric regulation of phosphofructokinase, whereas frequency control is distributed over the reaction network. Notably, the NAD+/NADH ratio modulates the frequency of the oscillations without affecting the instability. This is important for understanding the mutual synchronization of oscillations in the individual yeast cells, as synchronization is believed to occur via acetaldehyde, which in turn affects the frequency of oscillations by changing this ratio. PMID:15943800

Madsen, Mads F; Danø, Sune; Sørensen, Preben G

2005-06-01

181

Remote switch actuator  

DOEpatents

The invention provides a device and method for actuating electrical switches remotely. The device is removably attached to the switch and is actuated through the transfer of a user's force. The user is able to remain physically removed from the switch site obviating need for protective equipment. The device and method allow rapid, safe actuation of high-voltage or high-current carrying electrical switches or circuit breakers.

Haas, Edwin Gerard; Beauman, Ronald; Palo, Jr., Stefan

2013-01-29

182

Viral induced yeast apoptosis.  

PubMed

In an analogous system to mammals, induction of an apoptotic cell death programme (PCD) in yeast is not only restricted to various exogenous factors and stimuli, but can also be triggered by viral killer toxins and viral pathogens. In yeast, toxin secreting killer strains are frequently infected with double-stranded (ds)RNA viruses that are responsible for killer phenotype expression and toxin secretion in the infected host. In most cases, the viral toxins are either pore-forming proteins (such as K1, K2, and zygocin) that kill non-infected and sensitive yeast cells by disrupting cytoplasmic membrane function, or protein toxins (such as K28) that act in the nucleus by blocking DNA synthesis and subsequently causing a G1/S cell cycle arrest. Interestingly, while all these virus toxins cause necrotic cell death at high concentration, they trigger caspase- and ROS-mediated apoptosis at low-to-moderate concentration, indicating that even low toxin doses are deadly by triggering PCD in enemy cells. Remarkably, viral toxins are not solely responsible for cell death induction in vivo, as killer viruses themselves were shown to trigger apoptosis in non-infected yeast. Thus, as killer virus-infected and toxin secreting yeasts are effectively protected and immune to their own toxin, killer yeasts bear the intrinsic potential to dominate over time in their natural habitat. PMID:18291112

Schmitt, Manfred J; Reiter, Jochen

2008-07-01

183

Alarm toe switch  

Microsoft Academic Search

An alarm toe switch inserted within a shoe for energizing an alarm circuit in a covert manner includes an insole mounting pad into which a miniature reed switch is fixedly molded. An elongated slot perpendicular to the reed switch is formed in the bottom surface of the mounting pad. A permanent cylindrical magnet positioned in the forward portion of the

Ganyard

1982-01-01

184

Alarm toe switch  

Microsoft Academic Search

An alarm toe switch inserted within a shoe for energizing an alarm circuit n a covert manner includes an insole mounting pad into which a miniature reed switch is fixedly molded. An elongated slot perpendicular to the reed switch is formed in the bottom surface of the mounting pad. A permanent cylindrical magnet positioned in the forward portion of the

Ganyard; Floyd P

1982-01-01

185

Latching type optical switch  

NASA Astrophysics Data System (ADS)

An optical switch on yttrium orthoferrite crystal is developed. The switch is of latching type and has an operating time of 100 ns. Matrices of switches are feasible due to the dimensions of the optical rotator of less than 2 mm3.

Didosyan, Y. S.; Hauser, H.; Fiala, W.; Nicolics, J.; Toriser, W.

2002-05-01

186

Triggered plasma opening switch  

DOEpatents

A triggerable opening switch for a very high voltage and current pulse includes a transmission line extending from a source to a load and having an intermediate switch section including a plasma for conducting electrons between transmission line conductors and a magnetic field for breaking the plasma conduction path and magnetically insulating the electrons when it is desired to open the switch.

Mendel, Clifford W. (Albuquerque, NM)

1988-01-01

187

[Mitochondria inheritance in yeast saccharomyces cerevisiae].  

PubMed

The review is devoted to the main mechanisms of mitochondria inheritance in yeast Saccharonmyces cerevisiae. The genetic mechanisms of functionally active mitochondria inheritance in eukaryotic cells is one of the most relevant in modem researches. A great number of genetic diseases are associated with mitochondria dysfunction. Plasticity of eukaryotic cell metabolism according to the environmental changes is ensured by adequate mitochondria functioning by means of ATP synthesis coordination, reactive oxygen species accumulation, apoptosis regulation and is an important factor of cell adaptation to stress. Mitochondria participation in important for cell vitality processes masters the presence of accurate mechanisms of mitochondria functions regulation according to environment fluctuations. The mechanisms of mitochondria division and distribution are highly conserved. Baker yeast S. cerevisiae is an ideal model object for mitochondria researches due to energetic metabolism lability, ability to switch over respiration to fermentation, and petite-positive phenotype. Correction of metabolism according to the environmental changes is necessary for cell vitality. The influence of respiratory, carbon, amino acid and phosphate metabolism on mitochondria functions was shown. As far as the mechanisms that stabilize functions of mitochondria and mtDNA are highly conserve, we can project yeast regularities on higher eukaryotes systems. This makes it possible to approximate understanding the etiology and pathogenesis of a great number of human diseases. PMID:21786681

Fizikova, A Iu

2011-01-01

188

Quantifying the Dynamics of Coupled Networks of Switches and Oscillators  

PubMed Central

Complex network dynamics have been analyzed with models of systems of coupled switches or systems of coupled oscillators. However, many complex systems are composed of components with diverse dynamics whose interactions drive the system's evolution. We, therefore, introduce a new modeling framework that describes the dynamics of networks composed of both oscillators and switches. Both oscillator synchronization and switch stability are preserved in these heterogeneous, coupled networks. Furthermore, this model recapitulates the qualitative dynamics for the yeast cell cycle consistent with the hypothesized dynamics resulting from decomposition of the regulatory network into dynamic motifs. Introducing feedback into the cell-cycle network induces qualitative dynamics analogous to limitless replicative potential that is a hallmark of cancer. As a result, the proposed model of switch and oscillator coupling provides the ability to incorporate mechanisms that underlie the synchronized stimulus response ubiquitous in biochemical systems.

Francis, Matthew R.; Fertig, Elana J.

2012-01-01

189

Aneuploidy underlies a multicellular phenotypic switch.  

PubMed

Although microorganisms are traditionally used to investigate unicellular processes, the yeast Saccharomyces cerevisiae has the ability to form colonies with highly complex, multicellular structures. Colonies with the "fluffy" morphology have properties reminiscent of bacterial biofilms and are easily distinguished from the "smooth" colonies typically formed by laboratory strains. We have identified strains that are able to reversibly toggle between the fluffy and smooth colony-forming states. Using a combination of flow cytometry and high-throughput restriction-site associated DNA tag sequencing, we show that this switch is correlated with a change in chromosomal copy number. Furthermore, the gain of a single chromosome is sufficient to switch a strain from the fluffy to the smooth state, and its subsequent loss to revert the strain back to the fluffy state. Because copy number imbalance of six of the 16 S. cerevisiae chromosomes and even a single gene can modulate the switch, our results support the hypothesis that the state switch is produced by dosage-sensitive genes, rather than a general response to altered DNA content. These findings add a complex, multicellular phenotype to the list of molecular and cellular traits known to be altered by aneuploidy and suggest that chromosome missegregation can provide a quick, heritable, and reversible mechanism by which organisms can toggle between phenotypes. PMID:23812752

Tan, Zhihao; Hays, Michelle; Cromie, Gareth A; Jeffery, Eric W; Scott, Adrian C; Ahyong, Vida; Sirr, Amy; Skupin, Alexander; Dudley, Aimée M

2013-07-23

190

Aneuploidy underlies a multicellular phenotypic switch  

PubMed Central

Although microorganisms are traditionally used to investigate unicellular processes, the yeast Saccharomyces cerevisiae has the ability to form colonies with highly complex, multicellular structures. Colonies with the “fluffy” morphology have properties reminiscent of bacterial biofilms and are easily distinguished from the “smooth” colonies typically formed by laboratory strains. We have identified strains that are able to reversibly toggle between the fluffy and smooth colony-forming states. Using a combination of flow cytometry and high-throughput restriction-site associated DNA tag sequencing, we show that this switch is correlated with a change in chromosomal copy number. Furthermore, the gain of a single chromosome is sufficient to switch a strain from the fluffy to the smooth state, and its subsequent loss to revert the strain back to the fluffy state. Because copy number imbalance of six of the 16 S. cerevisiae chromosomes and even a single gene can modulate the switch, our results support the hypothesis that the state switch is produced by dosage-sensitive genes, rather than a general response to altered DNA content. These findings add a complex, multicellular phenotype to the list of molecular and cellular traits known to be altered by aneuploidy and suggest that chromosome missegregation can provide a quick, heritable, and reversible mechanism by which organisms can toggle between phenotypes.

Tan, Zhihao; Hays, Michelle; Cromie, Gareth A.; Jeffery, Eric W.; Scott, Adrian C.; Ahyong, Vida; Sirr, Amy; Skupin, Alexander; Dudley, Aimee M.

2013-01-01

191

Oxygen requirements of yeasts.  

PubMed Central

Type species of 75 yeast genera were examined for their ability to grow anaerobically in complex and mineral media. To define anaerobic conditions, we added a redox indicator, resazurin, to the media to determine low redox potentials. All strains tested were capable of fermenting glucose to ethanol in oxygen-limited shake-flask cultures, even those of species generally regarded as nonfermentative. However, only 23% of the yeast species tested grew under anaerobic conditions. A comparative study with a number of selected strains revealed that Saccharomyces cerevisiae stands out as a yeast capable of rapid growth at low redox potentials. Other yeasts, such as Torulaspora delbrueckii and Candida tropicalis, grew poorly mu max, 0.03 and 0.05 h-1, respectively) under anaerobic conditions in mineral medium supplemented with Tween 80 and ergosterol. The latter organisms grew rapidly under oxygen limitation and then displayed a high rate of alcoholic fermentation. It can be concluded that these yeasts have hitherto-unidentified oxygen requirements for growth. Images

Visser, W; Scheffers, W A; Batenburg-van der Vegte, W H; van Dijken, J P

1990-01-01

192

Mapping Yeast Transcriptional Networks  

PubMed Central

The term “transcriptional network” refers to the mechanism(s) that underlies coordinated expression of genes, typically involving transcription factors (TFs) binding to the promoters of multiple genes, and individual genes controlled by multiple TFs. A multitude of studies in the last two decades have aimed to map and characterize transcriptional networks in the yeast Saccharomyces cerevisiae. We review the methodologies and accomplishments of these studies, as well as challenges we now face. For most yeast TFs, data have been collected on their sequence preferences, in vivo promoter occupancy, and gene expression profiles in deletion mutants. These systematic studies have led to the identification of new regulators of numerous cellular functions and shed light on the overall organization of yeast gene regulation. However, many yeast TFs appear to be inactive under standard laboratory growth conditions, and many of the available data were collected using techniques that have since been improved. Perhaps as a consequence, comprehensive and accurate mapping among TF sequence preferences, promoter binding, and gene expression remains an open challenge. We propose that the time is ripe for renewed systematic efforts toward a complete mapping of yeast transcriptional regulatory mechanisms.

Hughes, Timothy R.; de Boer, Carl G.

2013-01-01

193

21 CFR 172.896 - Dried yeasts.  

Code of Federal Regulations, 2013 CFR

...172.896 Dried yeasts. Dried yeast (Saccharomyces cerevisiae and Saccharomyces fragilis ) and dried torula yeast (Candida utilis ) may be safely used in food provided the total folic acid content of the yeast does not exceed 0.04 milligram...

2013-04-01

194

Decreased ethyl carbamate generation during Chinese rice wine fermentation by disruption of CAR1 in an industrial yeast strain.  

PubMed

Saccharomyces cerevisiae metabolizes arginine to ornithine and urea during wine fermentations. In the fermentation of Chinese rice wine, yeast strains of S. cerevisiae do not fully metabolize urea, which will be secreted into the spirits and spontaneously reacts with ethanol to form ethyl carbamate, a potential carcinogenic agent for humans. To block the pathway of urea production, we genetically engineered two haploid strains to reduce the arginase (encoded by CAR1) activity, which were isolated from a diploid industrial Chinese rice wine strain. Finally the engineered haploids with opposite mating type were mated back to diploid strains, obtaining a heterozygous deletion strain (CAR1/car1) and a homozygous defect strain (car1/car1). These strains were compared to the parental industrial yeast strain in Chinese rice wine fermentations and spirit production. The strain with the homozygous CAR1 deletion showed significant reductions of urea and EC in the final spirits in comparison to the parental strain, with the concentration reductions by 86.9% and 50.5% respectively. In addition, EC accumulation was in a much lower tempo during rice wine storage. Moreover, the growth behavior and fermentation characteristics of the engineered diploid strain were similar to the parental strain. PMID:24769164

Wu, Dianhui; Li, Xiaomin; Shen, Chao; Lu, Jian; Chen, Jian; Xie, Guangfa

2014-06-16

195

Yeast killer systems.  

PubMed Central

The killer phenomenon in yeasts has been revealed to be a multicentric model for molecular biologists, virologists, phytopathologists, epidemiologists, industrial and medical microbiologists, mycologists, and pharmacologists. The surprisingly widespread occurrence of the killer phenomenon among taxonomically unrelated microorganisms, including prokaryotic and eukaryotic pathogens, has engendered a new interest in its biological significance as well as its theoretical and practical applications. The search for therapeutic opportunities by using yeast killer systems has conceptually opened new avenues for the prevention and control of life-threatening fungal diseases through the idiotypic network that is apparently exploited by the immune system in the course of natural infections. In this review, the biology, ecology, epidemiology, therapeutics, serology, and idiotypy of yeast killer systems are discussed.

Magliani, W; Conti, S; Gerloni, M; Bertolotti, D; Polonelli, L

1997-01-01

196

Virtual Yeast Cell  

NSDL National Science Digital Library

Learning about the various parts of a cell can be tricky business, but this virtual yeast cell offered by The University of Nottingham will come in handy for biology students and science instructors. This learning resource was created to help students in the brewing science program learn about yeast cytology, though just about anyone with an interest in cells will learn something from visiting the site. After entering the interactive cell, visitors can click on different parts of the cell (such as the cytoplasm or the nucleus) in order to learn more about the importance of each one. Visitors should remember that they can also download the virtual yeast cell and use it in the classroom or just with a group of friends.

2008-02-28

197

Virtual Yeast Cell  

NSDL National Science Digital Library

Learning about the various parts of a cell can be tricky business, but this virtual yeast cell offered by The University of Nottingham will come in handy for biology students and science instructors. This learning resource was created to help students in the brewing science program learn about yeast cytology, though just about anyone with an interest in cells will learn something from visiting the site. After entering the interactive cell, visitors can click on different parts of the cell (such as the cytoplasm or the nucleus) in order to learn more about the importance of each one. Visitors should remember that they can also download the virtual yeast cell and use it in the classroom or just with a group of friends.

198

Vaginal Yeast Infections (For Parents)  

MedlinePLUS

... a common infection caused by a yeast called candida albicans (a type of fungus). Yeast infections usually ... the vagina, it is known as vulvovaginal candidiasis . Candida can overgrow for many reasons. Stress, pregnancy, and ...

199

L-arabinose fermenting yeast  

DOEpatents

An L-arabinose utilizing yeast strain is provided for the production of ethanol by introducing and expressing bacterial araA, araB and araD genes. L-arabinose transporters are also introduced into the yeast to enhance the uptake of arabinose. The yeast carries additional genomic mutations enabling it to consume L-arabinose, even as the only carbon source, and to produce ethanol. Methods of producing ethanol include utilizing these modified yeast strains. ##STR00001##

Zhang, Min (Lakewood, CO); Singh, Arjun (Lakewood, CO); Knoshaug, Eric (Golden, CO); Franden, Mary Ann (Centennial, CO); Jarvis, Eric (Boulder, CO); Suominen, Pirkko (Maple Grove, MN)

2010-12-07

200

Effective switching frequency multiplier inverter  

DOEpatents

A switching frequency multiplier inverter for low inductance machines that uses parallel connection of switches and each switch is independently controlled according to a pulse width modulation scheme. The effective switching frequency is multiplied by the number of switches connected in parallel while each individual switch operates within its limit of switching frequency. This technique can also be used for other power converters such as DC/DC, AC/DC converters.

Su, Gui-Jia (Oak Ridge, TN); Peng, Fang Z. (Okemos, MI)

2007-08-07

201

An acoustic switch.  

PubMed

The benefits derived from the development of acoustic transistors which act as switches or amplifiers have been reported in the literature. Here we propose a model of acoustic switch. We theoretically demonstrate that the device works: the input signal is totally restored at the output when the switch is on whereas the output signal nulls when the switch is off. The switch, on or off, depends on a secondary acoustic field capable to manipulate the main acoustic field. The model relies on the attenuation effect of many oscillating bubbles on the main travelling wave in the liquid, as well as on the capacity of the secondary acoustic wave to move the bubbles. This model evidences the concept of acoustic switch (transistor) with 100% efficiency. PMID:23816529

Vanhille, Christian; Campos-Pozuelo, Cleofé

2014-01-01

202

Solid state switch  

DOEpatents

A solid state switch, with reverse conducting thyristors, is designed to operate at 20 kV hold-off voltage, 1500 A peak, 1.0 .mu.s pulsewidth, and 4500 pps, to replace thyratrons. The solid state switch is more reliable, more economical, and more easily repaired. The switch includes a stack of circuit card assemblies, a magnetic assist and a trigger chassis. Each circuit card assembly contains a reverse conducting thyristor, a resistor capacitor network, and triggering circuitry.

Merritt, Bernard T. (Livermore, CA); Dreifuerst, Gary R. (Livermore, CA)

1994-01-01

203

AC magnetohydrodynamic microfluidic switch  

SciTech Connect

A microfluidic switch has been demonstrated using an AC Magnetohydrodynamic (MHD) pumping mechanism in which the Lorentz force is used to pump an electrolytic solution. By integrating two AC MHD pumps into different arms of a Y-shaped fluidic circuit, flow can be switched between the two arms. This type of switch can be used to produce complex fluidic routing, which may have multiple applications in {micro}TAS.

Lemoff, A V; Lee, A P

2000-03-02

204

Evaluation of YeastIdent and Uni-Yeast-Tek yeast identification systems.  

PubMed Central

The accuracy of the new API YeastIdent system and the Flow Laboratories Uni-Yeast-Tek identification kit with an expanded data base was evaluated in comparison to the API 20C yeast identification system by three laboratories. A total of 489 test isolates were used, biased toward yeasts commonly encountered in clinical specimens. Isolates not in a system's data base were not counted in the evaluation of that system. For isolates in their data base, YeastIdent was 55% accurate and Uni-Yeast-Tek was 40% accurate. By the manufacturer's criteria of reliable identification without additional tests, both systems failed to identify many common and uncommon species. The limited number of substrates and difficulties in assessing results obtained with 11 of the API YeastIdent substrates and apparent errors in the expanded Uni-Yeast-Tek data base appeared to be major factors limiting the accuracy of these systems.

Salkin, I F; Land, G A; Hurd, N J; Goldson, P R; McGinnis, M R

1987-01-01

205

Reusable fast opening switch  

DOEpatents

A reusable fast opening switch for transferring energy, in the form of a high power pulse, from an electromagnetic storage device such as an inductor into a load. The switch is efficient, compact, fast and reusable. The switch comprises a ferromagnetic semiconductor which undergoes a fast transition between conductive and insulating states at a critical temperature and which undergoes the transition without a phase change in its crystal structure. A semiconductor such as europium rich europhous oxide, which undergoes a conductor to insulator transition when it is joule heated from its conductor state, can be used to form the switch.

Van Devender, John P. (Albuquerque, NM); Emin, David (Albuquerque, NM)

1986-01-01

206

Reusable fast opening switch  

DOEpatents

A reusable fast opening switch for transferring energy, in the form of a high power pulse, from an electromagnetic storage device such as an inductor into a load. The switch is efficient, compact, fast and reusable. The switch comprises a ferromagnetic semiconductor which undergoes a fast transition between conductive and metallic states at a critical temperature and which undergoes the transition without a phase change in its crystal structure. A semiconductor such as europium rich europhous oxide, which undergoes a conductor to insulator transition when it is joule heated from its conductor state, can be used to form the switch.

Van Devender, J.P.; Emin, D.

1983-12-21

207

Alarm toe switch  

DOEpatents

An alarm toe switch inserted within a shoe for energizing an alarm circuit n a covert manner includes an insole mounting pad into which a miniature reed switch is fixedly molded. An elongated slot perpendicular to the reed switch is formed in the bottom surface of the mounting pad. A permanent cylindrical magnet positioned in the forward portion of the slot with a diameter greater than the pad thickness causes a bump above the pad. A foam rubber block is also positioned in the slot rearwardly of the magnet and holds the magnet in normal inoperative relation. A non-magnetic support plate covers the slot and holds the magnet and foam rubber in the slot. The plate minimizes bending and frictional forces to improve movement of the magnet for reliable switch activation. The bump occupies the knuckle space beneath the big toe. When the big toe is scrunched rearwardly the magnet is moved within the slot relative to the reed switch, thus magnetically activating the switch. When toe pressure is released the foam rubber block forces the magnet back into normal inoperative position to deactivate the reed switch. The reed switch is hermetically sealed with the magnet acting through the wall so the switch assembly S is capable of reliable operation even in wet and corrosive environments.

Ganyard, Floyd P. (Albuquerque, NM)

1982-01-01

208

Mutagen testing with yeast.  

PubMed

This article deals primarily with the practical aspects of mutagen testing with yeast. Equipment necessary for a laboratory where mutagen testing with yeast is performed, and the most commonly used media, are listed. Some general procedures are described and, finally, for those who have little experience with work of this kind, a precise protocol is given for an experiment with stationary phase cells of the strain D7 of Saccharomyces cerevisiae using the heteroallelic ade2 system as the genetic endpoint. Some experimental data were obtained by students following this protocol using the direct-acting mutagen ethyl methanesulfonate (EMS); these data are discussed and analyzed. More details on the various genetic endpoints available in numerous yeast strains and on the interpretation of dose-dependence data, as well as an extended list of yeast literature, can be found in an article by Eckardt and von Borstel in this volume. Further technical advice is provided in our references to Zimmermann (1975), von Borstel (1981), and Zimmermann et al. (1984). PMID:3904715

Eckardt, F; Siede, W

1985-01-01

209

30 GHz tuned MEMS switches  

Microsoft Academic Search

This paper demonstrates the use of resonant tuning in high-isolation reflective MEMS electrostatic switches. Tuned switches can achieve higher isolation and a lower pulldown voltage than a comparable single element switch. An equivalent circuit model was developed for individual shunt capacitive membrane switches and then implemented in tuned circuits. The novel cross switch was developed on a high resistivity silicon.

Jeremy B. Muldavin; Gabriel M. Rebeiz

1999-01-01

210

Visually Activated Switch System (VASS).  

National Technical Information Service (NTIS)

The Visually Activated Switching System (VASS) provides a simple means for control system switching during 'hands-on' flight. Switching is accomplished by looking at a cockpit switch and operating a single trigger switch on the stick or throttle. A helmet...

E. Potter P. Burkott J. Gordon

1976-01-01

211

L-arabinose fermenting yeast  

DOEpatents

An L-arabinose utilizing yeast strain is provided for the production of ethanol by introducing and expressing bacterial araA, araB and araD genes. L-arabinose transporters are also introduced into the yeast to enhance the uptake of arabinose. The yeast carries additional genomic mutations enabling it to consume L-arabinose, even as the only carbon source, and to produce ethanol. A yeast strain engineered to metabolize arabinose through a novel pathway is also disclosed. Methods of producing ethanol include utilizing these modified yeast strains.

Zhang, Min; Singh, Arjun; Suominen, Pirkko; Knoshaug, Eric; Franden, Mary Ann; Jarvis, Eric

2013-02-12

212

Optical pseudospark switch  

Microsoft Academic Search

This patent discloses a high voltage, high current, multichannel, optically-triggered switch with the potential for improved lifetime of operation. Triggering of the switch is accomplished by ultraviolet illumination of multiple cathode apertures via fiber optic cables. The trigger optics for each channel, being composed of a fiber-optic cable terminated by some collimating optics, are protected from damaging metalization by enclosing

Michael G. Grothaus; Jack S. Bernardes; David C. Stoudt

1995-01-01

213

Optical Switching Devices.  

National Technical Information Service (NTIS)

An optical switching device employs a rare earth bis-phthalocyanine having third-order nonlinear susceptibilities. In a preferred optical switch, the rare earth bis-phthalocyanine is employed as a nonlinear optical material body that fills the space betwe...

M. E. Boyle J. S. Shirk

1991-01-01

214

Chin Activated Switch.  

National Technical Information Service (NTIS)

The patent application relates to a chin activated switch which is used in directing the movement of a binocular microscope or other surgical equipment and has particular utility in vitreous surgery. A chin activated switch for use in adjusting the moveme...

C. J. McCarthy S. Charles D. M. Eichenbaum

1975-01-01

215

The Electrical Switch  

NSDL National Science Digital Library

This activity is inquiry-based in that students will perform the activity before they formally learn about how a switch works. They will use a multimeter to discover the different settings on a triple-throw switch. The teacher should show the students how

Horton, Michael

2009-05-30

216

Reflective HTS switch  

DOEpatents

A HTS switch includes a HTS conductor for providing a superconducting path for an electrical signal and an serpentine wire actuator for controllably heating a portion of the conductor sufficiently to cause that portion to have normal, and not superconducting, resistivity. Mass of the portion is reduced to decrease switching time.

Martens, Jon S. (Albuquerque, NM); Hietala, Vincent M. (Placitas, NM); Hohenwarter, Gert K. G. (Madison, WI)

1994-01-01

217

Reflective HTS switch  

DOEpatents

A HTS (High Temperature Superconductor) switch includes a HTS conductor for providing a superconducting path for an electrical signal and an serpentine wire actuator for controllably heating a portion of the conductor sufficiently to cause that portion to have normal, and not superconducting, resistivity. Mass of the portion is reduced to decrease switching time. 6 figs.

Martens, J.S.; Hietala, V.M.; Hohenwarter, G.K.G.

1994-09-27

218

Paying Customers to Switch  

Microsoft Academic Search

This paper studies the business practice of offering discounts to new customers in markets with switching costs. In a two-period homogeneous-good duopoly model, it is shown that the equilibrium amount of discounts increases continuously in the expected switching costs of a typical consumer. In equilibrium, firms offer the same prices and discounts in a mature market even if they have

Yongmin Chen

1997-01-01

219

High energy semiconductor switch  

NASA Astrophysics Data System (ADS)

The objective was a controller for electric motors. By operating standard Nema B induction motors at variable speed a great deal of energy is saved. This is especially true in pumping and air conditioning applications. To allow wider use of variable speed AC drives, and to provide improved performance, a better semiconductor switch was sought. This was termed the High Energy Semiconductor Switch.

Risberg, R. L.

1989-02-01

220

Binary Switch Key.  

National Technical Information Service (NTIS)

The code key provides an information code pattern for a switching network. The code key is a portable self contained switch setting device employing spring loaded key pins, protected by a retractable skirt and a positive locking plate for securing the pin...

E. C. Bean C. J. Creveling

1965-01-01

221

A Novel Molecular Switch  

PubMed Central

Transcriptional regulation is a fundamental process for regulating the flux of all metabolic pathways. For the last several decades, the lac operon has served as a valuable model for studying transcription. More recently, the switch that controls the operon has also been successfully adapted to function in mammalian cells. Here we describe how, using directed evolution, we have created a novel switch that recognizes an asymmetric operator sequence. The new switch has a repressor with altered headpiece domains for operator recognition, and a redesigned dimer interface to create a heterodimeric repressor. Quite unexpectedly, the heterodimeric switch functions better than the natural system. It can repress more tightly than the naturally occurring switch of the lac operon; it is less leaky and can be induced more efficiently. Ultimately these novel repressors could be evolved to recognize eukaryotic promoters and used to regulate gene expression in mammalian systems.

Daber, Robert; Lewis, Mitchell

2009-01-01

222

Extracellular Polysaccharides Produced by Yeasts and Yeast-Like Fungi  

NASA Astrophysics Data System (ADS)

Several yeasts and yeast-like fungi are known to produce extracellular polysaccharides. Most of these contain D-mannose, either alone or in combination with other sugars or phosphate. A large chemical and structural variability is found between yeast species and even among different strains. The types of polymers that are synthesized can be chemically characterized as mannans, glucans, phosphoman-nans, galactomannans, glucomannans and glucuronoxylomannans. Despite these differences, almost all of the yeast exopolysaccharides display some sort of biological activity. Some of them have already applications in chemistry, pharmacy, cosmetics or as probiotic. Furthermore, some yeast exopolysaccharides, such as pullulan, exhibit specific physico-chemical and rheological properties, making them useful in a wide range of technical applications. A survey is given here of the production, the characteristics and the application potential of currently well studied yeast extracellular polysaccharides.

van Bogaert, Inge N. A.; de Maeseneire, Sofie L.; Vandamme, Erick J.

223

Yeast-Hyphal Dimorphism  

Microsoft Academic Search

All fungi have some capacity to grow in two basic morphological forms — spheres and tubes — therefore it could be argued that\\u000a they are all, to some extent, dimorphic. For many filamentous fungi spherical growth may only be expressed during the formation\\u000a of spores and many yeast-like fungi have only the remnants of a true filamentous growth habit. However,

N. A. R. Gow

224

Yeast Colony Embedding Method  

PubMed Central

Patterning of different cell types in embryos is a key mechanism in metazoan development. Communities of microorganisms, such as colonies and biofilms also display patterns of cell types. For example, in the yeast S. cerevisiae, sporulated cells and pseudohyphal cells are not uniformly distributed in colonies. The functional importance of patterning and the molecular mechanisms that underlie these patterns are still poorly understood. One challenge with respect to investigating patterns of cell types in fungal colonies is that unlike metazoan tissue, cells in colonies are relatively weakly attached to one another. In particular, fungal colonies do not contain the same extensive level of extracellular matrix found in most tissues . Here we report on a method for embedding and sectioning yeast colonies that reveals the interior patterns of cell types in these colonies. The method can be used to prepare thick sections (0.5 ?) useful for light microscopy and thin sections (0.1 ?) suitable for transmission electron microscopy. Asci and pseudohyphal cells can easily be distinguished from ovoid yeast cells by light microscopy , while the interior structure of these cells can be visualized by EM. The method is based on surrounding colonies with agar, infiltrating them with Spurr's medium, and then sectioning. Colonies with a diameter in the range of 1-2 mm are suitable for this protocol. In addition to visualizing the interior of colonies, the method allows visualization of the region of the colony that invades the underlying agar.

Piccirillo, Sarah; Honigberg, Saul M.

2011-01-01

225

The evolution of phenotypic switching in subdivided populations.  

PubMed

Stochastic switching is an example of phenotypic bet hedging, where offspring can express a phenotype different from that of their parents. Phenotypic switching is well documented in viruses, yeast, and bacteria and has been extensively studied when the selection pressures vary through time. However, there has been little work on the evolution of phenotypic switching under both spatially and temporally fluctuating selection pressures. Here we use a population genetic model to explore the interaction of temporal and spatial variation in determining the evolutionary dynamics of phenotypic switching. We find that the stable switching rate is mainly determined by the rate of environmental change and the migration rate. This stable rate is also a decreasing function of the recombination rate, although this is a weaker effect than those of either the period of environmental change or the migration rate. This study highlights the interplay of spatial and temporal environmental variability, offering new insights into how migration can influence the evolution of phenotypic switching rates, mutation rates, or other sources of phenotypic variation. PMID:24496012

Carja, Oana; Liberman, Uri; Feldman, Marcus W

2014-04-01

226

Anomalous resistive switching phenomenon  

NASA Astrophysics Data System (ADS)

Resistive switching was observed in Pt/SrTiO3/Pt capacitor devices. The switching depends on both the amplitude and polarity of the applied voltage and cannot be described as either bipolar or unipolar resistive switching. We term this behavior antipolar due to the opposite polarity of the set voltage relative to the previous reset voltage. A model based on electron injection by tunneling at interfaces and a Poole-Frenkel mechanism through the bulk is proposed. This model is quantified by use of a simple mathematical equation to simulate the experimental results.

Mojarad, Shahin A.; Goss, J. P.; Kwa, Kelvin S. K.; Petrov, Peter K.; Zou, Bin; Alford, Neil; O'Neill, Anthony

2012-12-01

227

Photoconductive switch package  

DOEpatents

A photoconductive switch is formed of a substrate that has a central portion of SiC or other photoconductive material and an outer portion of cvd-diamond or other suitable material surrounding the central portion. Conducting electrodes are formed on opposed sides of the substrate, with the electrodes extending beyond the central portion and the edges of the electrodes lying over the outer portion. Thus any high electric fields produced at the edges of the electrodes lie outside of and do not affect the central portion, which is the active switching element. Light is transmitted through the outer portion to the central portion to actuate the switch.

Ca[rasp, George J

2013-10-22

228

ISS of Switched Systems and Applications to Switching Adaptive Control  

Microsoft Academic Search

In this paper we prove that a switched nonlinear system has several useful ISS-type properties under average dwell-time switching signals if each constituent dynamical system is ISS. This extends available results for switched linear systems. We apply our result to stabilization of uncertain nonlinear systems via switching supervisory control, and show that the plant states can be kept bounded in

L. Vu; D. Chatterjee; D. Liberzon

2005-01-01

229

Parasite epigenetics and immune evasion: lessons from budding yeast  

PubMed Central

The remarkable ability of many parasites to evade host immunity is the key to their success and pervasiveness. The immune evasion is directly linked to the silencing of the members of extended families of genes that encode for major parasite antigens. At any time only one of these genes is active. Infrequent switches to other members of the gene family help the parasites elude the immune system and cause prolonged maladies. For most pathogens, the detailed mechanisms of gene silencing and switching are poorly understood. On the other hand, studies in the budding yeast Saccharomyces cerevisiae have revealed similar mechanisms of gene repression and switching and have provided significant insights into the molecular basis of these phenomena. This information is becoming increasingly relevant to the genetics of the parasites. Here we summarize recent advances in parasite epigenetics and emphasize the similarities between S. cerevisiae and pathogens such as Plasmodium, Trypanosoma, Candida, and Pneumocystis. We also outline current challenges in the control and the treatment of the diseases caused by these parasites and link them to epigenetics and the wealth of knowledge acquired from budding yeast.

2013-01-01

230

Switch Actuator Mechanism.  

National Technical Information Service (NTIS)

The switch actuator mechanism has utility as a circuit arming device in bombs which are dropped from aircraft. The mechanism includes a plunger having a sleeve mounted thereon, spring detent mechanism cooperating with the sleeve whereby the sleeve is mova...

S. Yerkovich

1965-01-01

231

Solar array switching unit  

NASA Technical Reports Server (NTRS)

A solar array switching (SASU) unit (22) according to the present invention includes a control system (24), a solar cell array (26) and switch circuits (28). The SASU unit (22) is associated with a power card (30) for receiving an output from the array (26). The array (26) has a number (0.5Y) of rows (38) each of which includes a pair of cell strings (42) separated by one of the switch circuits (28). Each of the strings (42) includes a number (X) of cells in electrical series. The SASU (22) switches the array (26) between a short string configuration where the array (26) effectively includes Y strings of X length, and a long string configuration where the array (26) effectively includes 0.5Y strings of 2X length. The SASU (22) thereby facilitates the use of solar power for space missions where solar intensity, operating temperature or other factors vary significantly.

Craig, Jr., Calvin L. (Inventor)

2000-01-01

232

Basics of Safety Switches  

NSDL National Science Digital Library

This course is one of the quickStep series offered by Siemens in Safety Switches. These are FREE on-line industrial knowledge building tutorials. quickSTEPs are a great start for industry novices moving into technical jobs or staff in operational support rolls. They can also be very effectively used as out of class assignments for review or to build fundamental skills. Each course includes: an online tutorial organized as a number of units, lessons with self check quiz questions, a glossary of terms, a self-check final exam with scoring, an extensive downloadable PDF study guide. This course offers: current protection, fuses, enclosures, switch design, switch terminology, safety switches, a final exam, a glossary and a 72 page study guide.

2008-11-25

233

An optical switch  

DOEpatents

The invention is a gas mixture for a diffuse discharge switch having an electron attaching gas wherein electron attachment is brought about by indirect excitation of molecules to long live states by exposure to laser light. 3 figs.

Christophorou, L.G.; Hunter, S.R.

1987-04-30

234

Optical Switch Evaluation Support.  

National Technical Information Service (NTIS)

Extensive testing has been done on nonlinear interface optical switch (NIOS) devices fabricated from laser deposited nonstoichiometric tungsten oxide films. A Fresnel coefficient formalism for evaluating the indices of refraction of the films has been dev...

J. Chaiken

1993-01-01

235

Plasmonic enhanced ultrafast switch.  

SciTech Connect

Ultrafast electronic switches fabricated from defective material have been used for several decades in order to produce picosecond electrical transients and TeraHertz radiation. Due to the ultrashort recombination time in the photoconductor materials used, these switches are inefficient and are ultimately limited by the amount of optical power that can be applied to the switch before self-destruction. The goal of this work is to create ultrafast (sub-picosecond response) photoconductive switches on GaAs that are enhanced through plasmonic coupling structures. Here, the plasmonic coupler primarily plays the role of being a radiation condenser which will cause carriers to be generated adjacent to metallic electrodes where they can more efficiently be collected.

Subramania,Ganapathi Subramanian; Reno, John Louis; Passmore, Brandon Scott; Harris, Tom.; Shaner, Eric Arthur; Barrick, Todd A.

2009-09-01

236

Switching power supply filter  

NASA Technical Reports Server (NTRS)

A filter for a switching power supply. The filter includes a common mode inductor with coil configurations allowing differential mode current from a dc source to pass through but attenuating common mode noise from the power supply so that the noise does not reach the dc source. The invention also includes the use of feed through capacitors at the switching power supply input terminals to provide further high-frequency noise attenuation.

Kumar, Prithvi R. (Inventor); Abare, Wayne (Inventor)

1989-01-01

237

Improved optical pseudospark switch  

Microsoft Academic Search

Disclosed is a high-voltage, high-current, multichannel, optically-triggered switch with the potential for improved lifetime of operation. Triggering of the switch is accomplished by ultraviolet illumination of multiple cathode apertures via fiber-optic cables. The trigger optics for each channel, being composed of a fiber-optic cable terminated by some collimating optics, are protected from damaging metalization by enclosing them in an angled

Michael G. Grothaus; Jack S. Bernardes; David C. Stoudt

1993-01-01

238

uv preilluminated gas switches  

SciTech Connect

We have designed, built, and characterized uv preilluminated gas switches for a trigger circuit and a low inductance discharge circuit. These switches have been incorporated into a 54 x 76 x 150 cm pulser module to produce a 1 Ma output current rising at 5 x 10/sup 12/ amps/sec with 1 ns jitter. Twenty such modules will be used on the Nova Inertial Confinement Fusion Laser System for plasma retropulse shutters.

Bradley, L.P.; Orham, E.L.; Stowers, I.F.; Braucht, J.R.

1980-06-03

239

Switch Card Apparatus and Methods.  

National Technical Information Service (NTIS)

Switch card apparatus are disclosed. In one embodiment, a circuit includes a first portion having a first switch adapted to be coupled to a first voltage, a second portion including a second switch, and a third portion including a third switch. The first ...

G. H. Smith H. N. Nguyen R. A. Kubinski T. T. Phan

2004-01-01

240

A radiation hard vacuum switch  

DOEpatents

A vacuum switch with an isolated trigger probe which is not directly connected to the switching electrodes. The vacuum switch within the plasmatron is triggered by plasma expansion initiated by the trigger probe which travels through an opening to reach the vacuum switch elements. The plasma arc created is directed by the opening to the space between the anode and cathode of the vacuum switch to cause conduction. 3 figs.

Boettcher, G.E.

1988-07-19

241

Circuit Techniques for Improving the Switching Loci of Transistor Switches in Switching Regulators  

Microsoft Academic Search

The use of switching regulator circuits at high power levels and high frequencies requires careful examination and control of the power dissipation during switching, which may be the dominant loss. In this paper it is shown that it is possible to remove most of the switching losses from the switching transistor with two networks, each containing three components: an inductor

E. T. Calkin; B. H. Hamilton

1976-01-01

242

Yeast interactions and wine flavour  

Microsoft Academic Search

Wine is the product of complex interactions between fungi, yeasts and bacteria that commence in the vineyard and continue throughout the fermentation process until packaging. Although grape cultivar and cultivation provide the foundations of wine flavour, microorganisms, especially yeasts, impact on the subtlety and individuality of the flavour response. Consequently, it is important to identify and understand the ecological interactions

Graham H. Fleet

2003-01-01

243

Yeast as a screening tool  

Microsoft Academic Search

The versatile genetic malleability of yeast, and the high degree of conservation between its cellular processes and those of human cells, have made it the model of choice for pioneering research in molecular and cell biology over the past four decades. These character- istics of yeast, taken together with technical advan- tages such as simple growth conditions, rapid cell division

Alcide Barberis; Tea Gunde; Catherine Berset; Stephan Audetat; Urs Lüthi

2005-01-01

244

Monitoring polyglutamine toxicity in yeast.  

PubMed

Experiments in yeast have significantly contributed to our understanding of general aspects of biochemistry, genetics, and cell biology. Yeast models have also delivered deep insights in to the molecular mechanism underpinning human diseases, including neurodegenerative diseases. Many neurodegenerative diseases are associated with the conversion of a protein from a normal and benign conformation into a disease-associated and toxic conformation - a process called protein misfolding. The misfolding of proteins with abnormally expanded polyglutamine (polyQ) regions causes several neurodegenerative diseases, such as Huntington's disease and the Spinocerebellar Ataxias. Yeast cells expressing polyQ expansion proteins recapitulate polyQ length-dependent aggregation and toxicity, which are hallmarks of all polyQ-expansion diseases. The identification of modifiers of polyQ toxicity in yeast revealed molecular mechanisms and cellular pathways that contribute to polyQ toxicity. Notably, several of these findings in yeast were reproduced in other model organisms and in human patients, indicating the validity of the yeast polyQ model. Here, we describe different expression systems for polyQ-expansion proteins in yeast and we outline experimental protocols to reliably and quantitatively monitor polyQ toxicity in yeast. PMID:21144902

Duennwald, Martin L

2011-03-01

245

Energy losses in switches  

SciTech Connect

The authors experiments show energy losses between 2 and 10 times that of the resistive time predictions. The experiments used hydrogen, helium, air, nitrogen, SF{sub 6} polyethylene, and water for the switching dielectric. Previously underestimated switch losses have caused over predicting the accelerator outputs. Accurate estimation of these losses is now necessary for new high-efficiency pulsed power devices where the switching losses constitute the major portion of the total energy loss. They found that the switch energy losses scale as (V{sub peak}I{sub peak}){sup 1.1846}. When using this scaling, the energy losses in any of the tested dielectrics are almost the same. This relationship is valid for several orders of magnitude and suggested a theoretical basis for these results. Currents up to .65 MA, with voltages to 3 MV were applied to various gaps during these experiments. The authors data and the developed theory indicates that the switch power loss continues for a much longer time than the resistive time, with peak power loss generally occurring at peak current in a ranging discharge instead of the early current time. All of the experiments were circuit code modeled after developing a new switch loss version based on the theory. The circuit code predicts switch energy loss and peak currents as a function of time. During analysis of the data they noticed slight constant offsets between the theory and data that depended on the dielectric. They modified the plasma conductivity for each tested dielectric to lessen this offset.

Martin, T.H.; Seamen, J.F.; Jobe, D.O.

1993-07-01

246

Modelling the yeast interactome.  

PubMed

The topology behind biological interaction networks has been studied for over a decade. Yet, there is no definite agreement on the theoretical models which best describe protein-protein interaction (PPI) networks. Such models are critical to quantifying the significance of any empirical observation regarding those networks. Here, we perform a comprehensive analysis of yeast PPI networks in order to gain insights into their topology and its dependency on interaction-screening technology. We find that: (1) interaction-detection technology has little effect on the topology of PPI networks; (2) topology of these interaction networks differs in organisms with different cellular complexity (human and yeast); (3) clear topological difference is present between PPI networks, their functional sub-modules, and their inter-functional "linkers"; (4) high confidence PPI networks have more "geometrical" topology compared to predicted, incomplete, or noisy PPI networks; and (5) inter-functional "linker" proteins serve as mediators in signal transduction, transport, regulation and organisational cellular processes. PMID:24589662

Janji?, Vuk; Sharan, Roded; Pržulj, Nataša

2014-01-01

247

Red yeast rice for dysipidemia.  

PubMed

Red yeast rice is an ancient Chinese food product that contains monacolins, chemical substances that are similar to statins in their mechanisms of action and lipid lowering properties. Several studies have found red yeast rice to be moderately effective at improving the lipid profile, particularly for lowering the low-density lipoprotein cholesterol levels. One large randomized controlled study from China found that red yeast rice significantly improved risk of major adverse cardiovascular events and overall survival in patients following myocardial infarction. Thus, red yeast rice is a potentially useful over-the-counter cholesterol-lowering agent. However, many red yeast rice formulations are non-standardized and unregulated food supplements, and there is a need for further research and regulation of production. PMID:24003656

Shamim, Shariq; Al Badarin, Firas J; DiNicolantonio, James J; Lavie, Carl J; O'Keefe, James H

2013-01-01

248

Programmed nuclear destruction in yeast  

PubMed Central

Studies of the budding yeast Saccharomyces cerevisiae have provided many of the most important insights into the mechanisms of autophagy, which are common to all eukaryotes. However, investigation of yeast self-destruction pathways, including autophagy and programmed cell death, has been almost exclusively restricted to cells undergoing vegetative growth, leaving very little exploration of their functions during developmental transitions in the yeast life cycle. We have recently discovered that whole nuclei are subject to programmed destruction during yeast gametogenesis. Programmed nuclear destruction (PND) possesses characteristics of apoptosis in the form of DNA cleavage by endonuclease G, and involves bulk protein turnover through an unusual autophagic pathway involving lysis of the vacuole rather than delivery of components to it through macroautophagy. We thus illuminate an example of developmentally programmed cellular “self-eating” in yeast, which is associated with the rupture of a lytic organelle, reminiscent of programmed cell death mechanisms in plants and animals.

Eastwood, Michael D.; Cheung, Sally W.T.; Meneghini, Marc D.

2013-01-01

249

Functional dissection of the global repressor Tup1 in yeast: dominant role of the C-terminal repression domain.  

PubMed Central

In the yeast Saccharomyces cerevisiae, Tup1, in association with Cyc8 (Ssn6), functions as a general repressor of transcription. Tup1 and Cyc8 are required for repression of diverse families of genes coordinately controlled by glucose repression, mating type, and other mechanisms. This repression is mediated by recruitment of the Cyc8-Tup1 complex to target promoters by sequence-specific DNA-binding proteins. We created a library of XhoI linker insertions and internal in-frame deletion mutations within the TUP1 coding region. Insertion mutations outside of the WD domains were wild type, while insertions within the WD domains induced mutant phenotypes with differential effects on the target genes SUC2, MFA2, RNR2, and HEM13. Deletion mutations confirmed previous findings of two separate repression domains in the N and C termini. The cumulative data suggest that the C-terminal repression domain, located near the first WD repeat, plays the dominant role in repression. Although the N-terminal repression domain is sufficient for partial repression, deletion of this region does not compromise repression. Surprisingly, deletion of the majority of the histone-binding domain of Tup1 also does not significantly reduce repression. The N-terminal region containing potential alpha-helical coiled coils is required for Tup1 oligomerization and association with Cyc8. Association with Cyc8 is required for repression of SUC2, HEM13, and RNR2 but not MFA2 and STE2.

Zhang, Zhizhou; Varanasi, Ushasri; Trumbly, Robert J

2002-01-01

250

Switching power supply  

DOEpatents

The invention is a repratable capacitor charging, switching power supply. A ferrite transformer steps up a dc input. The transformer primary is in a full bridge configuration utilizing power MOSFETs as the bridge switches. The transformer secondary is fed into a high voltage, full wave rectifier whose output is connected directly to the energy storage capacitor. The transformer is designed to provide adequate leakage inductance to limit capacitor current. The MOSFETs are switched to the variable frequency from 20 to 50 kHz to charge a capacitor from 0.6 kV. The peak current in a transformer primary and secondary is controlled by increasing the pulse width as the capacitor charges. A digital ripple counter counts pulses and after a preselected desired number is reached an up-counter is clocked.

Mihalka, A.M.

1984-06-05

251

Thermionic gas switch  

DOEpatents

A temperature responsive thermionic gas switch having folded electron emitting surfaces. An ionizable gas is located between the emitter and an interior surface of a collector, coaxial with the emitter. In response to the temperature exceeding a predetermined level, sufficient electrons are derived from the emitter to cause the gas in the gap between the emitter and collector to become ionized, whereby a very large increase in current in the gap occurs. Due to the folded emitter surface area of the switch, increasing the "on/off" current ratio and adjusting the "on" current capacity is accomplished.

Hatch, George L. (San Francisco, CA); Brummond, William A. (Livermore, CA); Barrus, Donald M. (San Jose, CA)

1986-01-01

252

Magnetic switches and circuits  

SciTech Connect

This report outlines the use of saturable inductors as switches in lumped-element, magnetic-pulse compression circuits is discussed and the characteristic use of each is defined. In addition, the geometric constraints and magnetic pulse compression circuits used in short-pulse, low-inductance systems are considered. The scaling of presaturation leakage currents, magnetic energy losses, and switching times with geometrical and material parameters are developed to aid in evaluating magnetic pulse compression systems in a particular application. Finally, a scheme for increasing the couping coefficient in saturable stripline transformers is proposed to enable their use in the short-pulse, high-voltage regime.

Nunnally, W.C.

1982-05-01

253

Bearingless switched reluctance motor  

NASA Technical Reports Server (NTRS)

A switched reluctance motor has a stator with a first set of poles directed toward levitating a rotor horizontally within the stator. A disc shaped portion of a hybrid rotor is affected by the change in flux relative to the current provided at these levitation poles. A processor senses the position of the rotor and changes the flux to move the rotor toward center of the stator. A second set of poles of the stator are utilized to impart torque upon a second portion of the rotor. These second set of poles are driven in a traditional switched reluctance manner by the processor.

Morrison, Carlos R. (Inventor)

2004-01-01

254

Polyglutamine misfolding in yeast  

PubMed Central

Protein misfolding is associated with many human diseases, including neurodegenerative diseases, such as Alzheimer disease, Parkinson disease and Huntington disease. Protein misfolding often results in the formation of intracellular or extracellular inclusions or aggregates. Even though deciphering the role of these aggregates has been the object of intense research activity, their role in protein misfolding diseases is unclear. Here, I discuss the implications of studies on polyglutamine aggregation and toxicity in yeast and other model organisms. These studies provide an excellent experimental and conceptual paradigm that contributes to understanding the differences between toxic and protective trajectories of protein misfolding. Future studies like the ones discussed here have the potential to transform basic concepts of protein misfolding in human diseases and may thus help to identify new therapeutic strategies for their treatment.

2011-01-01

255

Expanding Yeast Knowledge Online  

PubMed Central

The completion of the Saccharomyces cerevisiae genome sequencing project11 and the continued development of improved technology for large-scale genome analysis have led to tremendous growth in the amount of new yeast genetics and molecular biology data. Efficient organization, presentation, and dissemination of this information are essential if researchers are to exploit this knowledge. In addition, the development of tools that provide efficient analysis of this information and link it with pertinent information from other systems is becoming increasingly important at a time when the complete genome sequences of other organisms are becoming available. The aim of this review is to familiarize biologists with the type of data resources currently available on the World Wide Web (WWW).

DOLINSKI, KARA; BALL, CATHERINE A.; CHERVITZ, STEPHEN A.; DWIGHT, SELINA S.; HARRIS, MIDORI A.; ROBERTS, SHANNON; ROE, TAIYUN; CHERRY, J. MICHAEL; BOTSTEIN, DAVID

2011-01-01

256

49 CFR 236.6 - Hand-operated switch equipped with switch circuit controller.  

Code of Federal Regulations, 2013 CFR

...2013-10-01 2013-10-01 false Hand-operated switch equipped with switch...Instructions: All Systems General § 236.6 Hand-operated switch equipped with switch circuit controller. Hand-operated switch equipped...

2013-10-01

257

High Power Optical Microwave Switches  

NASA Astrophysics Data System (ADS)

The RF distribution and pulse compression systems of the Next Linear Collider could benefit from a microwave switch that could handle few hundred megawatts^1. We present a rigorous analysis form an abstract point of view for the design of high power microwave switches. In our analysis we show how the design can be made to accomplish three goals. First, when the switch is off, the electric fields on the active elements are low. Second, when the switch is on, the losses in the active elements should be below a certain level, finally, one needs to limit the switching time to satisfy the application at hand. We first study the case of a single switch, and then expand our analysis to the case of multiple switches. We also give a design example. ^1 Sami G. Tantawi et. al. "Active radio frequency pulse compression using switched resonant delay lines," Nuclear Instruments and Methods in Physics Research A. Vol. 370 , 1996, pp. 297-302

Tantawi, S. G.; Ruth, R. D.; Vlieks, A. E.

1997-05-01

258

Remotely-Actuated Biomedical Switch.  

National Technical Information Service (NTIS)

The report describes an implantable electronic switch that may be remotely actuated by an rf impulse to operate low-voltage bioinstrumentation attached to or also implanted in the monitored subject. This switching circuitry's unique characteristic lies in...

1969-01-01

259

Kiowa Creek Switching Station  

SciTech Connect

The Western Area Power Administration (Western) proposes to construct, operate, and maintain a new Kiowa Creek Switching Station near Orchard in Morgan County, Colorado. Kiowa Creek Switching Station would consist of a fenced area of approximately 300 by 300 feet and contain various electrical equipment typical for a switching station. As part of this new construction, approximately one mile of an existing 115-kilovolt (kV) transmission line will be removed and replaced with a double circuit overhead line. The project will also include a short (one-third mile) realignment of an existing line to permit connection with the new switching station. In accordance with the Council on Environmental Quality (CEQ) regulations for implementing the procedural provisions of the National Environmental Policy Act of 1969 (NEPA), 40 CFR Parts 1500--1508, the Department of Energy (DOE) has determined that an environmental impact statement (EIS) is not required for the proposed project. This determination is based on the information contained in this environmental assessment (EA) prepared by Western. The EA identifies and evaluates the environmental and socioeconomic effects of the proposed action, and concludes that the advance impacts on the human environment resulting from the proposed project would not be significant. 8 refs., 3 figs., 1 tab.

Not Available

1990-03-01

260

Public digital switching systems  

Microsoft Academic Search

INCE the‘ expansion of telephony to cover long distances, an extensive network of compatible switching nodes, transmission terminals and facilities, and signaling protocols have been developed and deployed the world over. Today one may call over this integrated network to reach any of over 500 million telephone stations. The telephone today is as it was intended by Alexander Graham Bell-a

1983-01-01

261

Switched fragmented aperture antennas  

Microsoft Academic Search

This paper introduces a reconfigurable aperture concept derived from fragmented aperture design where the configuration of the fragmented aperture may be switched by the user to obtain different functionalities. A fragmented aperture antenna is a patchwork of discrete conducting and dielectric units distributed over the specified aperture. The arrangement of the units is determined using an efficient, multistage procedure that

James C. Maloney; Morris P. Kesler; Lisa M. Lust; Lon N. Pringle; T. Lynn Fountain; Paul H. Harms; Glenn S. Smith

2000-01-01

262

High Speed Packet Switching.  

National Technical Information Service (NTIS)

This document constitutes the final report prepared by Proteon, Inc. of Westborough, Massachusetts under contract NAS 5-30629 entitled High-Speed Packet Switching (SBIR 87-1, Phase 2) prepared for NASA-Greenbelt, Maryland. The primary goal of this researc...

1991-01-01

263

A Cdse Bistable Switch.  

National Technical Information Service (NTIS)

Under certain conditions of synthesis, cadmium selenide (CdSe) shows a hysteresis effect in its current-voltage relationship. The material, therefore, has been of interest for use as a switch to control the electroluminescent (EL) emission of a solid stat...

S. A. Harper, L. J. Nicastro

1967-01-01

264

Transparent electrode for optical switch  

DOEpatents

The invention relates generally to optical switches and techniques for applying a voltage to an electro-optical crystal, and more particularly, to transparent electodes for an optical switch. System architectures for very large inertial confinement fusion (ICF) lasers require active optical elements with apertures on the order of one meter. Large aperture optical switches are needed for isolation of stages, switch-out from regenerative amplifier cavities and protection from target retroreflections.

Goldhar, J.; Henesian, M.A.

1984-10-19

265

Discovery of a "White-Gray-Opaque" Tristable Phenotypic Switching System in Candida albicans: Roles of Non-genetic Diversity in Host Adaptation  

PubMed Central

Non-genetic phenotypic variations play a critical role in the adaption to environmental changes in microbial organisms. Candida albicans, a major human fungal pathogen, can switch between several morphological phenotypes. This ability is critical for its commensal lifestyle and for its ability to cause infections. Here, we report the discovery of a novel morphological form in C. albicans, referred to as the “gray” phenotype, which forms a tristable phenotypic switching system with the previously reported white and opaque phenotypes. White, gray, and opaque cell types differ in a number of aspects including cellular and colony appearances, mating competency, secreted aspartyl proteinase (Sap) activities, and virulence. Of the three cell types, gray cells exhibit the highest Sap activity and the highest ability to cause cutaneous infections. The three phenotypes form a tristable phenotypic switching system, which is independent of the regulation of the mating type locus (MTL). Gray cells mate over 1,000 times more efficiently than do white cells, but less efficiently than do opaque cells. We further demonstrate that the master regulator of white-opaque switching, Wor1, is essential for opaque cell formation, but is not required for white-gray transitions. The Efg1 regulator is required for maintenance of the white phenotype, but is not required for gray-opaque transitions. Interestingly, the wor1/wor1 efg1/efg1 double mutant is locked in the gray phenotype, suggesting that Wor1 and Efg1 could function coordinately and play a central role in the regulation of gray cell formation. Global transcriptional analysis indicates that white, gray, and opaque cells exhibit distinct gene expression profiles, which partly explain their differences in causing infections, adaptation ability to diverse host niches, metabolic profiles, and stress responses. Therefore, the white-gray-opaque tristable phenotypic switching system in C. albicans may play a significant role in a wide range of biological aspects in this common commensal and pathogenic fungus.

Guan, Guobo; Dai, Yu; Nobile, Clarissa J.; Liang, Weihong; Cao, Chengjun; Zhang, Qiuyu; Zhong, Jin; Huang, Guanghua

2014-01-01

266

Engineering antibodies by yeast display.  

PubMed

Since its first application to antibody engineering 15 years ago, yeast display technology has been developed into a highly potent tool for both affinity maturing lead molecules and isolating novel antibodies and antibody-like species. Robust approaches to the creation of diversity, construction of yeast libraries, and library screening or selection have been elaborated, improving the quality of engineered molecules and certainty of success in an antibody engineering campaign and positioning yeast display as one of the premier antibody engineering technologies currently in use. Here, we summarize the history of antibody engineering by yeast surface display, approaches used in its application, and a number of examples highlighting the utility of this method for antibody engineering. PMID:22450168

Boder, Eric T; Raeeszadeh-Sarmazdeh, Maryam; Price, J Vincent

2012-10-15

267

Component Processes in Task Switching.  

ERIC Educational Resources Information Center

Studied task switching in 4 experiments involving 111 Israeli undergraduates. Results show the preparation for a task switch is not a by-product of general preparation by phasic alertness or predicting target onset and establish reconfiguration as a separate preparatory process. Suggests that there are at least three components of task switching

Meiran, Nachshon; Chorev, Ziv; Sapir, Ayelet

2000-01-01

268

Alarm toe switch. [Patent application  

Microsoft Academic Search

An alarm toe switch inserted within a shoe for energizing an alarm circuit in a covert manner includes an insole mounting pad into which a miniature reed switch is fixedly molded. An elongated slot perpendicular to the reed switch is formed in the bottom surface of the mounting pad. A permanent cylindrical magnet positioned in the forward portion of the

Ganyard

1980-01-01

269

Organic Materials For Optical Switching  

NASA Technical Reports Server (NTRS)

Equations predict properties of candidate materials. Report presents results of theoretical study of nonlinear optical properties of organic materials. Such materials used in optical switching devices for computers and telecommunications, replacing electronic switches. Optical switching potentially offers extremely high information throughout in compact hardware.

Cardelino, Beatriz H.

1993-01-01

270

Semiconductor ac static power switch  

NASA Technical Reports Server (NTRS)

Semiconductor ac static power switch has long life and high reliability, contains no moving parts, and operates satisfactorily in severe environments, including high vibration and shock conditions. Due to their resistance to shock and vibration, static switches are used where accidental switching caused by mechanical vibration or shock cannot be tolerated.

Vrancik, J.

1968-01-01

271

Language Switching and Language Competition  

ERIC Educational Resources Information Center

This study examined the asymmetrical language switching cost in a word reading task (Experiment 1) and in a categorization task (Experiment 2 and 3). In Experiment 1, Spanish-English bilinguals named words in first language (L1) and second language (L2) in a switching paradigm. They were slower to switch from their weaker L2 to their more dominant…

Macizo, Pedro; Bajo, Teresa; Paolieri, Daniela

2012-01-01

272

A 35 GHz Latching Switch  

Microsoft Academic Search

This paper describes the development of a lightweight fast-switching 35 GHz latching ferrite circulator, with an instantaneous bandwidth of 5%, and a switching time of less the 0.30 microseconds. The device is designed for use over the temperature range of -60° C to +100° C under dynamic operating conditions. It is particularly well suited for use as a switching element

William C. Passaro; James W. McManus

1966-01-01

273

Triacylglycerol lipases of the yeast  

Microsoft Academic Search

All eukaryotes including the yeast contain a lipid storage compartment which is named lipid particle, lipid droplet or oil\\u000a body. Lipids accumulating in this subcellular fraction serve as a depot of energy and building blocks for membrane lipid synthesis.\\u000a In the yeast, the major storage lipids are triacylglycerols (TGs) and steryl esters (SEs). An important step in the life cycle

Karlheinz Grillitsch; Günther Daum

2011-01-01

274

Sociobiology of the budding yeast.  

PubMed

Social theory has provided a useful framework for research with microorganisms. Here I describe the advantages and possible risks of using a well-known model organism, the unicellular yeast Saccharomyces cerevisiae, for sociobiological research. I discuss the problems connected with clear classification of yeast behaviour based on the fitnessbased Hamilton paradigm. Relevant traits include different types of communities, production of flocculins, invertase and toxins, and the presence of apoptosis. PMID:24736156

Wloch-Salamon, Dominika M

2014-04-01

275

High gain GaAs photoconductive semiconductor switches: Switch longevity  

SciTech Connect

Optically activated, high gain GaAs switches are being tested for many different pulsed power applications that require long lifetime (longevity). The switches have p and n contact metallization (with intentional or unintentional dopants) configured in such a way as to produce p-i-n or n-i-n switches. The longevity of the switches is determined by circuit parameters and by the ability of the contacts to resist erosion. This paper will describe how the switches performed in test-beds designed to measure switch longevity. The best longevity was achieved with switches made with diffused contacts, achieving over 50 million pulses at 10 A and over 2 million pulses at 80 A.

Loubriel, G.M.; Zutavern, F.J.; Mar, A. [and others

1998-07-01

276

Modeling Huntington disease in yeast  

PubMed Central

Yeast have been extensively used to model aspects of protein folding diseases, yielding novel mechanistic insights and identifying promising candidate therapeutic targets. In particular, the neurodegenerative disorder Huntington disease (HD), which is caused by the abnormal expansion of a polyglutamine tract in the huntingtin (htt) protein, has been widely studied in yeast. This work has led to the identification of several promising therapeutic targets and compounds that have been validated in mammalian cells, Drosophila and rodent models of HD. Here we discuss the development of yeast models of mutant htt toxicity and misfolding, as well as the mechanistic insights gleaned from this simple model. The role of yeast prions in the toxicity/misfolding of mutant htt is also highlighted. Furthermore, we provide an overview of the application of HD yeast models in both genetic and chemical screens, and the fruitful results obtained from these approaches. Finally, we discuss the future of yeast in neurodegenerative research, in the context of HD and other diseases.

Mason, Robert P

2011-01-01

277

Boolean Network Model Predicts Knockout Mutant Phenotypes of Fission Yeast  

PubMed Central

Boolean networks (or: networks of switches) are extremely simple mathematical models of biochemical signaling networks. Under certain circumstances, Boolean networks, despite their simplicity, are capable of predicting dynamical activation patterns of gene regulatory networks in living cells. For example, the temporal sequence of cell cycle activation patterns in yeasts S. pombe and S. cerevisiae are faithfully reproduced by Boolean network models. An interesting question is whether this simple model class could also predict a more complex cellular phenomenology as, for example, the cell cycle dynamics under various knockout mutants instead of the wild type dynamics, only. Here we show that a Boolean network model for the cell cycle control network of yeast S. pombe correctly predicts viability of a large number of known mutants. So far this had been left to the more detailed differential equation models of the biochemical kinetics of the yeast cell cycle network and was commonly thought to be out of reach for models as simplistic as Boolean networks. The new results support our vision that Boolean networks may complement other mathematical models in systems biology to a larger extent than expected so far, and may fill a gap where simplicity of the model and a preference for an overall dynamical blueprint of cellular regulation, instead of biochemical details, are in the focus.

Davidich, Maria I.; Bornholdt, Stefan

2013-01-01

278

49 CFR 213.135 - Switches.  

Code of Federal Regulations, 2013 CFR

...switch point shall fit its stock rail properly, with the switch...vertical movement of a stock rail in the switch plates or of a switch plate on a tie shall not adversely affect the...the switch point to the stock rail. Broken or cracked switch...

2013-10-01

279

Metabolic regulation of yeast  

NASA Astrophysics Data System (ADS)

Metabolic regulation which is based on endogeneous and exogeneous process variables which may act constantly or time dependently on the living cell is discussed. The observed phenomena of the regulation are the result of physical, chemical, and biological parameters. These parameters are identified. Ethanol is accumulated as an intermediate product and the synthesis of biomass is reduced. This regulatory effect of glucose is used for the aerobic production of ethanol. Very high production rates are thereby obtained. Understanding of the regulation mechanism of the glucose effect has improved. In addition to catabolite repression, several other mechanisms of enzyme regulation have been described, that are mostly governed by exogeneous factors. Glucose also affects the control of respiration in a third class of yeasts which are unable to make use of ethanol as a substrate for growth. This is due to the lack of any anaplerotic activity. As a consequence, diauxic growth behavior is reduced to a one-stage growth with a drastically reduced cell yield. The pulse chemostat technique, a systematic approach for medium design is developed and medium supplements that are essential for metabolic control are identified.

Fiechter, A.

1982-12-01

280

Kinetic analysis of yeast galactokinase: implications for transcriptional activation of the GAL genes  

Microsoft Academic Search

Galactokinase (EC 2.7.1.6) catalyses the first step in the catabolism of galactose. Yeast galactokinase, Gal1p, and the closely related but catalytically inactive Gal3p, also function as ligand sensors in the GAL genetic switch. In the presence of galactose and ATP (the substrates of the reaction catalysed by Gal1p) Gal1p or Gal3p can bind to Gal80p, a transcriptional repressor. This relieves

David J. Timson; Richard J. Reece

2002-01-01

281

Intragenic Suppressor Mutations Restore GTPase and Translation Functions of a Eukaryotic Initiation Factor 5B Switch II Mutant?  

PubMed Central

Structural studies of GTP-binding proteins identified the Switch I and Switch II elements as contacting the ?-phosphate of GTP and undergoing marked conformational changes upon GTP versus GDP binding. Movement of a universally conserved Gly at the N terminus of Switch II is thought to trigger the structural rearrangement of this element. Consistently, we found that mutation of this Gly in the Switch II element of the eukaryotic translation initiation factor 5B (eIF5B) from Saccharomyces cerevisiae impaired cell growth and the guanine nucleotide-binding, GTPase, and ribosomal subunit joining activities of eIF5B. In a screen for mutations that bypassed the critical requirement for this Switch II Gly in eIF5B, intragenic suppressors were identified in the Switch I element and at a residue in domain II of eIF5B that interacts with Switch II. The intragenic suppressors restored yeast cell growth and eIF5B nucleotide-binding, GTP hydrolysis, and subunit joining activities. We propose that the Switch II mutation distorts the geometry of the GTP-binding active site, impairing nucleotide binding and the eIF5B domain movements associated with GTP binding. Accordingly, the Switch I and domain II suppressor mutations induce Switch II to adopt a conformation favorable for nucleotide binding and hydrolysis and thereby reestablish coupling between GTP binding and eIF5B domain movements.

Shin, Byung-Sik; Acker, Michael G.; Maag, David; Kim, Joo-Ran; Lorsch, Jon R.; Dever, Thomas E.

2007-01-01

282

Switched matrix accelerator  

SciTech Connect

We describe a new concept for a microwave circuit functioning as a charged-particle accelerator at mm wavelengths, permitting an accelerating gradient higher than conventional passive circuits can withstand consistent with cyclic fatigue. The device provides acceleration for multiple bunches in parallel channels, and permits a short exposure time for the conducting surface of the accelerating cavities. Our analysis includes scalings based on a smooth transmission line model and a complementary treatment with a coupled-cavity simulation. We also provide an electromagnetic design for the accelerating structure, arriving at rough dimensions for a seven-cell accelerator matched to standard waveguide and suitable for bench tests at low power in air at 91.392 GHz. A critical element in the concept is a fast mm-wave switch suitable for operation at high power, and we present the considerations for implementation in an H-plane tee. We discuss the use of diamond as the photoconductor switch medium.

Whittum, David H.; Tantawi, Sami G.

2001-01-01

283

Plasma opening switch  

DOEpatents

A command triggered plasma opening switch assembly using an amplification stage. The assembly surrounds a coaxial transmission line and has a main plasma opening switch (POS) close to the load and a trigger POS upstream from the main POS. The trigger POS establishes two different current pathways through the assembly depended on whether it has received a trigger current pulse. The initial pathway has both POS's with plasma between their anodes and cathodes to form a short across the transmission line and isolating the load. The final current pathway is formed when the trigger POS receives a trigger current pulse which energizes its fast coil to push the conductive plasma out from between its anode and cathode, allowing the main transmission line current to pass to the fast coil of the main POS, thus pushing its plasma out the way so as to establish a direct current pathway to the load.

Savage, Mark E. (Albuquerque, NM); Mendel, Jr., Clifford W. (Albuquerque, NM)

2001-01-01

284

Quantized conductance atomic switch.  

PubMed

A large variety of nanometre-scale devices have been investigated in recent years that could overcome the physical and economic limitations of current semiconductor devices. To be of technological interest, the energy consumption and fabrication cost of these 'nanodevices' need to be low. Here we report a new type of nanodevice, a quantized conductance atomic switch (QCAS), which satisfies these requirements. The QCAS works by controlling the formation and annihilation of an atomic bridge at the crossing point between two electrodes. The wires are spaced approximately 1 nm apart, and one of the two is a solid electrolyte wire from which the atomic bridges are formed. We demonstrate that such a QCAS can switch between 'on' and 'off' states at room temperature and in air at a frequency of 1 MHz and at a small operating voltage (600 mV). Basic logic circuits are also easily fabricated by crossing solid electrolyte wires with metal electrodes. PMID:15635405

Terabe, K; Hasegawa, T; Nakayama, T; Aono, M

2005-01-01

285

Switched optoelectronic microwave load  

NASA Astrophysics Data System (ADS)

The paper presents the analysis of a switched optoelectronic microwave load which can work either as a laser-controlled, matched or adjustable, resistive load or as a high-speed optoelectronic microwave switch. The device consists of a GaAs microstrip section controlled by a pulse-operated laser diode via substrate-edge-excitation. The exponential decay of photoconductivity across a longitudinal section of the microstrip forms a laser-induced electron-hole plasma wedge that works as a lossy tapered transmission-line section. The specific microwave power distribution within the excited region is derived in detail, as is the total input reflection coefficient under two special operating conditions (open-ended section and matched section). Numerical results are presented for a 906 nm excitation.

Platte, W.

1982-10-01

286

The quantum cryptographic switch  

NASA Astrophysics Data System (ADS)

We illustrate the principle of a cryptographic switch for a quantum scenario, in which a third party (Charlie) can control to a continuously varying degree the amount of information the receiver (Bob) receives, after the sender (Alice) has sent her information through a quantum channel. Suppose Charlie transmits a Bell state to Alice and Bob. Alice uses dense coding to transmit two bits to Bob. Only if the 2-bit information corresponding to the choice of the Bell state is made available by Charlie to Bob can the latter recover Alice's information. By varying the amount of information Charlie gives, he can continuously alter the information recovered by Bob. The performance of the protocol as subjected to the squeezed generalized amplitude damping channel is considered. We also present a number of practical situations where a cryptographic switch would be of use.

Srinatha, N.; Omkar, S.; Srikanth, R.; Banerjee, Subhashish; Pathak, Anirban

2014-01-01

287

Cryogenic switched MOSFET characterization  

NASA Technical Reports Server (NTRS)

Both p channel and n channel enhancement mode MOSFETs can be readily switched on and off at temperatures as low as 2.8 K so that switch sampled readout of a VLWIR Ge:Ga focal plane is electronically possible. Noise levels as low as 100 rms electrons per sample (independent of sample rate) can be achieved using existing p channel MOSFETs, at overall rates up to 30,000 samples/second per multiplexed channel (e.g., 32 detectors at a rate of almost 1,000 frames/second). Run of the mill devices, including very low power dissipation n channel FETs would still permit noise levels of the order of 500 electrons/sample.

1981-01-01

288

Future switching satellites  

NASA Technical Reports Server (NTRS)

Communications satellites of the future are likely to use much narrower beams in order to increase the uplink G/T and the downlink EIRP so that small earth terminals of the VSAT class can achieve full mesh connectivity. These satellites will need onboard switches to route traffic from originating upbeams to destination downbeams. This paper presents a new approach to accomplishing this rerouting using destination-directed packets that inherently carry the information needed to control the onboard switch connections and to adjust the traffic flow among the beams and the stations. The method also inherently provides channel multiplication and DAMA advantages which result in maximally efficient utilization of the space segment resource.

Campanella, S. Joseph; Pontano, Benjamin A.; Chalmers, Harvey

1988-01-01

289

Switching Power Supplies  

NSDL National Science Digital Library

Created by Work-Ready Electronics, a project of the Advanced Technological Education program, this module walks visitors through the basics of switching power supplies. The content of the site is divided into four areas: SMPS Basics and Switching Regulators; DC-DC Converters: Charge Pumps, Forwards Converters and Flyback Converters; Inverters, UPS and Hysteresis Curve, and SMPS: Advantages, Disadvantages and Troubleshooting. There is a quiz for each area in the Knowledge Probe area, and the Learning Resources section contains five activities to help cement student understanding. There are also further resources - both print and Web based - for more information and two Questors, a Flash trivia game. The Notebook function allows visitors to take notes and review them at any time. This is an excellent resource students and educators in electronics technician programs.

2008-09-05

290

Composite Material Switches  

NASA Technical Reports Server (NTRS)

A device to protect electronic circuitry from high voltage transients is constructed from a relatively thin piece of conductive composite sandwiched between two conductors so that conduction is through the thickness of the composite piece. The device is based on the discovery that conduction through conductive composite materials in this configuration switches to a high resistance mode when exposed to voltages above a threshold voltage.

Javadi, Hamid (Inventor)

2001-01-01

291

Composite Material Switches  

NASA Technical Reports Server (NTRS)

A device to protect electronic circuitry from high voltage transients is constructed from a relatively thin piece of conductive composite sandwiched between two conductors so that conduction is through the thickness of the composite piece. The device is based on the discovery that conduction through conductive composite materials in this configuration switches to a high resistance mode when exposed to voltages above a threshold voltage.

Javadi, Hamid (Inventor)

2002-01-01

292

CREE: Making the Switch  

ScienceCinema

CREE, with the help of ARPA-E funding, has developed a Silicon Carbide (SIC) transistor which can be used to create solid state transformers capable of meeting the unique needs of the emerging smart grid. SIC transistors are different from common silicon computer chips in that they handle grid scale voltages with ease and their high frequency switching is well suited to the intermittent nature of renewable energy generation.

Grider, David; Palmer, John

2014-04-09

293

Dectin-1 mediates macrophage recognition of Candida albicans yeast but not filaments  

PubMed Central

The ability of Candida albicans to rapidly and reversibly switch between yeast and filamentous morphologies is crucial to pathogenicity, and it is thought that the filamentous morphology provides some advantage during interaction with the mammalian immune system. Dectin-1 is a receptor that binds ?-glucans and is important for macrophage phagocytosis of fungi. The receptor also collaborates with Toll-like receptors for inflammatory activation of phagocytes by fungi. We show that yeast cell wall ?-glucan is largely shielded from Dectin-1 by outer wall components. However, the normal mechanisms of yeast budding and cell separation create permanent scars which expose sufficient ?-glucan to trigger antimicrobial responses through Dectin-1, including phagocytosis and activation of reactive oxygen production. During filamentous growth, no cell separation or subsequent ?-glucan exposure occurs, and the pathogen fails to activate Dectin-1. The data demonstrate a mechanism by which C. albicans shape alone directly contributes to the method by which phagocytes recognize the fungus.

Gantner, Benjamin N; Simmons, Randi M; Underhill, David M

2005-01-01

294

Lipoxygenase inhibitors shift the yeast/mycelium dimorphism in Ceratocystis ulmi.  

PubMed Central

The yeast-mycelium dimorphism in Ceratocystis ulmi, the causative agent of Dutch elm disease, was switched by gossypol, nordihydroguaiaretic acid, and propylgallate. In each case the mycelial form was converted to the yeast form. These compounds are recognized lipoxygenase inhibitors. Inhibitors of cyclooxygenase and thromboxane synthetase did not cause mycelia to shift to the yeast form. We suggest the following two-part hypothesis: (i) that lipoxygenase is a target for antifungal antibiotics and (ii) that many phytoalexins (antimicrobial compounds of plant origin) are targeted toward fungal lipoxygenases. In addition, in a study to determine potential lipoxygenase substrates, a fatty acid analysis indicated that C. ulmi conidiospores contained high levels of oleic, linoleic, and linolenic acids but no arachidonic acid.

Jensen, E C; Ogg, C; Nickerson, K W

1992-01-01

295

Optical switch fabric design for gigabit switching router  

NASA Astrophysics Data System (ADS)

One of the key issues of high performance IP Gigabit Switching Router (GSR) design is about switching fabrics. In the traditional bus-based router architectures, the data transfer rate of copper backplanes will soon reach the speed limit because of connector reflections and crosstalk. An alternative optical switching fabric technology is necessary in order to satisfy the demand for high switching bandwidth. In this paper we firstly present a novel all-optical broadcasting switch fabric design scheme based on broadcasting bus architecture. In this section we also illustrate the advantages and disadvantages of this kind of architecture and demonstrate that this kind of switching fabric architecture have no interior block as well as none I/O block. Second, we discuss such implementation scheme of all-optical broadcasting switch fabric architecture as queuing, scheduling and multicasting. Finally, we get a conclusion that all-optical broadcasting switch fabric is one of the cost-effective solutions to design high-speed, scalable and simple switch fabrics compared with those complicated electric crossbar switch fabrics in GSR design.

Wei, Wei; Zeng, QingJi

2001-10-01

296

Ultrafast gas switching experiments  

SciTech Connect

We describe recent experiments which studied the physics of ultrafast gas breakdown under the extreme overvoltages which occur when a high pressure gas switch is pulse charged to hundreds of kV in 1 ns or less. The highly overvolted peaking gaps produce powerful electromagnetic pulses with risetimes < 100 ps which can be used for ultrawideband radar systems, particle accelerators, laser drivers, bioelectromagnetic studies, electromagnetic effects testing, and for basic studies of gas breakdown physics. We have produced and accurately measured pulses with 50 to 100 ps risetimes to peak levels of 75 to 160 kV at pulse repetition frequencies (PRF) to I kHz. A unique gas switch was developed to hold off hundreds of kV with parasitic inductance less than I nH. An advanced diagnostic system using Fourier compensation was developed to measure single-shot risetimes below 35 ps. The complete apparatus is described and wave forms are presented. The measured data are compared with a theoretical model which predicts key features including dependence on gas species and pressure. We have applied this technology to practical systems driving ultrawideband radiating antennas and bounded wave simulators. For example, we have developed a thyristor/pulse transformer based system using a highly overvolted cable switch. This pulser driving a Sandia- designed TEM cell, provides an ultra wideband impulse with < 200 ps risetime to the test object at a PRF > 1 kHz at > 100 kV/m E field.

Frost, C.A.; Martin, T.H.; Patterson, P.E.; Rinehart, L.F.; Rohwein, G.J.; Roose, L.D.; Aurand, J.F.; Buttram, M.T.

1996-11-01

297

Organic optical bistable switch  

NASA Astrophysics Data System (ADS)

We demonstrate an organic optical bistable switch by integrating an efficient organic photodetector on top of a transparent electrophosphorescent organic light-emitting diode (TOLED). The bistability is achieved with an external field-effect transistor providing positive feedback. In the ``LOW'' state, the TOLED is off and the current in the photodetector is solely its dark current. In the ``HIGH'' state, the TOLED emits light that is directly coupled into the integrated photodetector through the transparent cathode. The photocurrent then is fed back to the TOLED, maintaining it in the HIGH state. The green electrophosphorescent material, fac tris(2-phenylpyridine) iridium [Ir(ppy)3] doped into a 4,4'-N,N'-dicarbazole-biphenyl host was used as the luminescent material in the TOLED, while alternating thin layers of copper phthalocyanine and 3,4,9,10-perylenetetracarboxylic bis-benzimidazole were used as the active region of the organic photodetector. The circuit has a 3 dB bandwidth of 25 kHz, and can be switched between HIGH and LOW using pulses as narrow as 60 ns. The bistable switch can be both electrically and optically reset, making it a candidate for image-retaining displays (e.g., electronic paper) and other photonic logic applications. The integrated organic device also has broad use as a linear circuit element in applications such as automatic brightness control.

Xue, Jiangeng; Forrest, Stephen R.

2003-01-01

298

Ferroelectric switching of elastin.  

PubMed

Ferroelectricity has long been speculated to have important biological functions, although its very existence in biology has never been firmly established. Here, we present compelling evidence that elastin, the key ECM protein found in connective tissues, is ferroelectric, and we elucidate the molecular mechanism of its switching. Nanoscale piezoresponse force microscopy and macroscopic pyroelectric measurements both show that elastin retains ferroelectricity at 473 K, with polarization on the order of 1 ?C/cm(2), whereas coarse-grained molecular dynamics simulations predict similar polarization with a Curie temperature of 580 K, which is higher than most synthetic molecular ferroelectrics. The polarization of elastin is found to be intrinsic in tropoelastin at the monomer level, analogous to the unit cell level polarization in classical perovskite ferroelectrics, and it switches via thermally activated cooperative rotation of dipoles. Our study sheds light onto a long-standing question on ferroelectric switching in biology and establishes ferroelectricity as an important biophysical property of proteins. This is a critical first step toward resolving its physiological significance and pathological implications. PMID:24958890

Liu, Yuanming; Cai, Hong-Ling; Zelisko, Matthew; Wang, Yunjie; Sun, Jinglan; Yan, Fei; Ma, Feiyue; Wang, Peiqi; Chen, Qian Nataly; Zheng, Hairong; Meng, Xiangjian; Sharma, Pradeep; Zhang, Yanhang; Li, Jiangyu

2014-07-01

299

A yeast-based rapid prototype platform for gene control elements in mammalian cells.  

PubMed

Programming genetic circuits in mammalian cells requires flexible, tunable, and user-tailored gene-control systems. However, most existing control systems are either mechanistically specific for microbial organisms or must be laboriously re-engineered to function in mammalian cells. Here, we demonstrate a ribozyme-based device platform that can be directly transported from yeast to mammalian cells in a "plug-and-play" manner. Ribozyme switches previously prototyped in yeast are shown to regulate gene expression in a predictable, ligand-responsive manner in human HEK 293, HeLa, and U2OS cell lines without any change to device sequence nor further optimization. The ribozyme-based devices, which exhibit activation ratios comparable to the best RNA-based regulatory devices demonstrated in mammalian cells to-date, retain their prescribed functions (ON or OFF switch), tunability of regulatory stringency, and responsiveness to different small-molecule inputs in mammalian hosts. Furthermore, we observe strong correlations of device performance between yeast and all mammalian cell lines tested (R(2) ?= 0.63-0.97). Our unique device architecture can therefore act as a rapid prototyping platform (RPP) based on a yeast chassis, providing a well-developed and genetically tractable system that supports rapid and high-throughput screens for generating gene-controllers with a broad range of functions in mammalian cells. This platform will accelerate development of mammalian gene-controllers for diverse applications, including cell-based therapeutics and cell-fate reprogramming. PMID:23184812

Wei, Kathy Y; Chen, Yvonne Y; Smolke, Christina D

2013-04-01

300

Heterothallism in Saccharomyces cerevisiae isolates from nature: effect of HO locus on the mode of reproduction  

PubMed Central

Understanding the evolution of sex and recombination, key factors in the evolution of life, is a major challenge in biology. Studies of reproduction strategies of natural populations are important to complement the theoretical and experimental models. Fungi with both sexual and asexual life cycles are an interesting system for understanding the evolution of sex. In a study of natural populations of yeast Saccharomyces cerevisiae, we found that the isolates are heterothallic, meaning their mating type is stable, while the general belief is that natural S. cerevisiae strains are homothallic (can undergo mating-type switching). Mating-type switching is a gene-conversion process initiated by a site-specific endonuclease HO; this process can be followed by mother–daughter mating. Heterothallic yeast can mate with unrelated haploids (amphimixis), or undergo mating between spores from the same tetrad (intratetrad mating, or automixis), but cannot undergo mother–daughter mating as homothallic yeasts can. Sequence analysis of HO gene in a panel of natural S. cerevisiae isolates revealed multiple mutations. Good correspondence was found in the comparison of population structure characterized using 19 microsatellite markers spread over eight chromosomes and the HO sequence. Experiments that tested whether the mating-type switching pathway upstream and downstream of HO is functional, together with the detected HO mutations, strongly suggest that loss of function of HO is the cause of heterothallism. Furthermore, our results support the hypothesis that clonal reproduction and intratetrad mating may predominate in natural yeast populations, while mother–daughter mating might not be as significant as was considered.

EZOV, TAL KATZ; CHANG, SHANG-LIN; FRENKEL, ZE'EV; SEGRE, AYELLET V.; BAHALUL, MORAN; MURRAY, ANDREW W.; LEU, JUN-YI; KOROL, ABRAHAM; KASHI, YECHEZKEL

2014-01-01

301

Candida zeylanoides: another opportunistic yeast.  

PubMed Central

A patient with a long history of scleroderma and gastrointestinal malabsorption requiring total parenteral nutrition was admitted with Candida zeylanoides fungemia. The yeast responded to therapy, but on two subsequent admissions for episodes of fever the blood cultures yielded the same yeast. The identity of the Candida species was established biochemically by both the API (Analytab) and Vitek system approaches. C. zeylanoides ATCC 20356 and ATCC 7351 served as controls for these analyses and for antifungal susceptibility studies and restriction endonuclease analyses of chromosomal DNA. These investigations indicated that representative isolates of the yeasts from the three episodes were identical and differed in several respects from the ATCC strains, which did not share many of the characteristics bands with the DNA restriction fragment analysis. C. zeylanoides variants capable of tolerating 35 degrees C can complicate the recovery of patients, especially individuals compromised by their underlying disease. Images

Levenson, D; Pfaller, M A; Smith, M A; Hollis, R; Gerarden, T; Tucci, C B; Isenberg, H D

1991-01-01

302

Cdc42 Oscillations in Yeasts  

NSDL National Science Digital Library

A fundamental problem in cell biology is how cells define one or several discrete sites of polarity. Through mechanisms involving positive and negative feedback, the small Rho-family guanosine triphosphatase Cdc42 breaks symmetry in round budding yeast cells to define a single site of polarized cell growth. However, it is not clear how cells can define multiple sites of polarization concurrently. We discuss a study in which rod-shaped fission yeast cells, which naturally polarize growth at their two cell ends, exhibited oscillations of Cdc42 activity between these sites. We compare these findings with similar oscillatory behavior of Cdc42 detected in budding yeast cells and discuss the possible mechanism and functional outputs of these oscillations.

Felipe O. Bendezu (Switzerland;University of Lausanne REV); Sophie G. Martin (Switzerland;University of Lausanne REV)

2012-12-04

303

Transient Responses of Yeasts to Glucose Excess.  

National Technical Information Service (NTIS)

The thesis describes the physiological responses of yeasts when they are transferred from glucose limitation to glucose excess. In certain organisms such as Saccharomyces cerevisiae, bakers' yeast, this change in environmental conditions results in an imm...

H. van Urk

1989-01-01

304

Disruption of Yeast Membranes by Methylphenidate.  

National Technical Information Service (NTIS)

Methylphenidate blocked sorbose uptake and loss by yeast spheroplasts and, at higher concentrations, disrupted spheroplasts. At high concentrations methylphenidate also ruptured the membranes of whole yeast cells; sorbose and 280 nm-absorbing materials we...

E. Spoerl

1970-01-01

305

Pentose utilization in yeasts: Physiology and biochemistry.  

National Technical Information Service (NTIS)

The fermentive performance of bacteria, yeasts, and filamentous fungi was investigated in a pentose (xylose)-rich lignocellulosic hydrolyzate. The filamentous fungus Fusarium oxysporum and the xylose-fermenting yeast Pichia stipitis were found to be very ...

H. Jeppson

1996-01-01

306

Yeast Can Affect Behavior and Learning.  

ERIC Educational Resources Information Center

A pediatrician recounts his experiences in diagnosing and treating allergies to common yeast germs that may result in behavior and learning problems. He lists characteristics that may predispose children to yeast-connected health problems. (CL)

Crook, William G.

1984-01-01

307

Monolithic integrated analog switching arrays  

Microsoft Academic Search

The reduction of the chip area of low ON-resistance transistor switches in n-channel metal oxide semiconductor-Si-gate technology to obtain higher density of monolithic integrated analog switching arrays is outlined. The applicability of the scaling principle, the reduction of the gate poly-Si line width and the use of a double diffusion process were studied. Transistor switches with two micron channel length

E. Baechle; J. Hersener; J. Koehne; M. Kuisl; K. Schlueter; A. Stuermer

1983-01-01

308

DNA-controlled excitonic switches.  

PubMed

Fluorescence resonance energy transfer (FRET) is a promising means of enabling information processing in nanoscale devices, but dynamic control over exciton pathways is required. Here, we demonstrate the operation of two complementary switches consisting of diffusive FRET transmission lines in which exciton flow is controlled by DNA. Repeatable switching is accomplished by the removal or addition of fluorophores through toehold-mediated strand invasion. In principle, these switches can be networked to implement any Boolean function. PMID:22401838

Graugnard, Elton; Kellis, Donald L; Bui, Hieu; Barnes, Stephanie; Kuang, Wan; Lee, Jeunghoon; Hughes, William L; Knowlton, William B; Yurke, Bernard

2012-04-11

309

The Yeast Nuclear Pore Complex  

PubMed Central

An understanding of how the nuclear pore complex (NPC) mediates nucleocytoplasmic exchange requires a comprehensive inventory of the molecular components of the NPC and a knowledge of how each component contributes to the overall structure of this large molecular translocation machine. Therefore, we have taken a comprehensive approach to classify all components of the yeast NPC (nucleoporins). This involved identifying all the proteins present in a highly enriched NPC fraction, determining which of these proteins were nucleoporins, and localizing each nucleoporin within the NPC. Using these data, we present a map of the molecular architecture of the yeast NPC and provide evidence for a Brownian affinity gating mechanism for nucleocytoplasmic transport.

Rout, Michael P.; Aitchison, John D.; Suprapto, Adisetyantari; Hjertaas, Kelly; Zhao, Yingming; Chait, Brian T.

2000-01-01

310

Power transistor switching characterization  

NASA Technical Reports Server (NTRS)

The switching properties of power transistors are investigated. The devices studied were housed in IO-3 cases and were of an n(+)-p-n(-)-n(+) vertical dopant structure. The effects of the magnitude of the reverse-base current and temperature on the reverse-bias second breakdown characteristics are discussed. Brief discussions of device degradation due to second breakdown and of a constant voltage turn-off circuit are included. A description of a vacuum tube voltage clamp circuit which reduces clamped collector voltage overshoot is given.

Blackburn, D. L.

1981-01-01

311

A terahertz molecular switch.  

PubMed

We present time-dependent results describing the current through a molecular device, modeled as a complex with two active centers connected to leads under bias. We show that, at a properly adjusted external voltage, a passing terahertz electromagnetic pulse may cause a transition between states of finite and negligible current, suggesting that the system might be useful as a nanoscopic switch in the terahertz range. A phase diagram defining the bias region in which the transition takes place within a short time is given. As described, the physical processes involved are of an entirely different nature than those in ordinary photodetectors. PMID:12786110

Orellana, P; Claro, F

2003-05-01

312

Neutron activated switch  

DOEpatents

A switch for reacting quickly to a neutron emission. A rod consisting of fissionable material is located inside a vacuum tight body. An adjustable contact is located coaxially at an adjustable distance from one end of the rod. Electrical leads are connected to the rod and to the adjustable contact. With a vacuum drawn inside the body, a neutron bombardment striking the rod causes it to heat and expand longitudinally until it comes into contact with the adjustable contact. This circuit closing occurs within a period of a few microseconds.

Barton, David M. (Espanola, NM)

1991-01-01

313

Biological switches and clocks  

PubMed Central

To introduce this special issue on biological switches and clocks, we review the historical development of mathematical models of bistability and oscillations in chemical reaction networks. In the 1960s and 1970s, these models were limited to well-studied biochemical examples, such as glycolytic oscillations and cyclic AMP signalling. After the molecular genetics revolution of the 1980s, the field of molecular cell biology was thrown wide open to mathematical modellers. We review recent advances in modelling the gene–protein interaction networks that control circadian rhythms, cell cycle progression, signal processing and the design of synthetic gene networks.

Tyson, John J.; Albert, Reka; Goldbeter, Albert; Ruoff, Peter; Sible, Jill

2008-01-01

314

Composite Thermal Switch  

NASA Technical Reports Server (NTRS)

Lithium primary and lithium ion secondary batteries provide high specific energy and energy density. The use of these batteries also helps to reduce launch weight. Both primary and secondary cells can be packaged as high-rate cells, which can present a threat to crew and equipment in the event of external or internal short circuits. Overheating of the cell interior from high current flows induced by short circuits can result in exothermic reactions in lithium primary cells and fully charged lithium ion secondary cells. Venting of the cell case, ejection of cell components, and fire have been reported in both types of cells, resulting from abuse, cell imperfections, or faulty electronic control design. A switch has been developed that consists of a thin layer of composite material made from nanoscale particles of nickel and Teflon that conducts electrons at room temperature and switches to an insulator at an elevated temperature, thus interrupting current flow to prevent thermal runaway caused by internal short circuits. The material is placed within the cell, as a thin layer incorporated within the anode and/or the cathode, to control excess currents from metal-to-metal or metal-to-carbon shorts that might result from cell crush or a manufacturing defect. The safety of high-rate cells is thus improved, preventing serious injury to personnel and sensitive equipment located near the battery. The use of recently available nanoscale particles of nickel and Teflon permits an improved, homogeneous material with the potential to be fine-tuned to a unique switch temperature, sufficiently below the onset of a catastrophic chemical reaction. The smaller particles also permit the formation of a thinner control film layer (<50 m), which can be incorporated into commercial high-rate lithium primary and secondary cells. The innovation permits incorporation in current lithium and lithium-ion cell designs with a minimal impact on cell weight and volume. The composite thermal switch (CTS(TradeMark)) coating can be incorporated in either the anode or cathode or both. The coating can be applied in a variety of different processes that permits incorporation in the cell and electrode manufacturing processes. The CTS responds quickly and halts current flow in the hottest parts of the cell first. The coating can be applied to metal foil and supplied as a cell component onto which the active electrode materials are coated.

McDonald, Robert; Brawn, Shelly; Harrison, Katherine; O'Toole, Shannon; Moeller, Michael

2011-01-01

315

Selection and improvement of wine yeasts  

Microsoft Academic Search

The selection of wine yeasts is usually carried out within the species Saccha- romyces cerevisiae. It aims at identifying the yeast strains that, besides fermenting grape juice vigorously and producing high ethanol yield, can also positively influence the com- position and the sensorial characteristics of wine. The natural availability of yeast strains possessing an ideal combination of oenological characteristics is

S. RAINIERI; I. S. PRETORIUS

316

Continuous ethanol production using induced yeast aggregates  

Microsoft Academic Search

The induction of yeast cell aggregates in a column reactor was initiated by packing yeast cell paste of Saccharomyces uvarum into the column, and then YMP broth was fed into the column from the bottom at a linear flow rate of 2.5 cm\\/h. Thereafter, yeast cells aggregated in the column within 48 h without a supply of oxygen. When this

LiFu Chen; Cheng-Shung Gong

1986-01-01

317

Yeast: A Research Organism for Teaching Genetics.  

ERIC Educational Resources Information Center

Explains why laboratory strains of bakers yeast, Saccharomyces cerevisiae, are particularly suited for classroom science activities. Describes the sexual life cycle of yeast and the genetic system with visible mutations. Presents an overview of activities that can be done with yeast and gives a source for teachers to obtain more information. (PR)

Manney, Thomas R.; Manney, Monta L.

1992-01-01

318

Enological functions of parietal yeast mannoproteins  

Microsoft Academic Search

Parietal yeast mannoproteins play a very important role in the overall vinification process. Their production and release, both during winemaking and aging on lees, depends on the specific yeast strain and the nutritional conditions. The following enological functions of parietal yeast mannoproteins have been described: (a) adsorption of ochratoxin A; (b) combination with phenolic compounds; (c) increased growth of malolactic

Andrea Caridi

2006-01-01

319

Phylogenetics of Saccharomycetales, the ascomycete yeasts  

Microsoft Academic Search

Ascomycete yeasts (phylum Ascomycota: subphylum Saccharomycotina: class Saccharomycetes: order Saccharomycetales) comprise a monophyletic lineage with a single order of about 1000 known species. These yeasts live as saprobes, often in association with plants, animals and their interfaces. A few species account for most human mycotic infections, and fewer than 10 species are plant pathogens. Yeasts are responsible for important industrial

Sung-Oui Suh; Meredith Blackwell; Cletus P. Kurtzman; M.-A. Lachance

2006-01-01

320

Beer brewing using a fusant between a sake yeast and a brewer's yeast  

Microsoft Academic Search

Beer brewing using a fusant between a sake yeast (a lysine auxotrophic mutant of sake yeast K-14) and a brewer's yeast (a respiratory-deficient mutant of the top fermentation yeast NCYC1333) was performed to take advantage of the beneficial characteristics of sake yeasts, i.e., the high productivity of esters, high tolerance to ethanol, and high osmotolerance. The fusant (F-32) obtained was

Nobuhiko Mukai; Chiharu Nishimori; Ikuko Wilson Fujishige; Akihiro Mizuno; Toshiro Takahashi; Kazuo Sato

2001-01-01

321

The critical temperature regions in resistive switching  

Microsoft Academic Search

Critical temperature regions for resistive switching were found based on HfAlO resistive switching memory. From 5 K to 300 K, the resistive switching appears at 60 K, and then a reversible bipolar switching between the two states is observed at above 150 K. It is suggested that the resistive switching characteristics of the binary transitional metal oxides are governed by

L. Chen; P. Zhou; Q. Q. Sun; S. J. Ding; A. Q. Jiang; D. W. Zhang

2011-01-01

322

Guaranteed scheduling for switches with configuration overhead  

Microsoft Academic Search

In this paper, we present three algorithms that provide performance guarantees for scheduling switches, such as optical switches, with configuration overhead. Each algorithm emulates an unconstrained (zero overhead) switch by accumulating a batch of configuration requests and generating a corresponding schedule for a constrained switch. Speedup is required both to cover the configuration overhead of the switch and to compensate

Brian Towles; William J. Dally

2003-01-01

323

Tuning the temperature dependence for switching in dithienylethene photochromic switches.  

PubMed

Diarylethene photochromic switches use light to drive structural changes through reversible electrocyclization reactions. High efficiency in dynamic photoswitching is a prerequisite for applications, as is thermal stability and the selective addressability of both isomers ring-opened and -closed diarylethenes. These properties can be optimized readily through rational variation in molecular structure. The efficiency with regard to switching as a function of structural variation is much less understood, with the exception of geometric requirements placed on the reacting atoms. Ultimately, increasing the quantum efficiency of photochemical switching in diarylethenes requires a detailed understanding of the excited-state potential energy surface(s) and the mechanisms involved in switching. Through studies of the temperature dependence, photoswitching and theoretical studies demonstrate the occurrence or absence of thermal activation barriers in three constitutional isomers that bear distinct ?-conjugated systems. We found that a decrease in the thermal barriers correlates with an increase in switching efficiency. The origin of the barriers is assigned to the decrease in ?-conjugation that is concomitant with the progress of the photoreaction. Furthermore, we show that balanced molecular design can minimize the change in the extent of ?-conjugation during switching and lead to optimal bidirectional switching efficiencies. Our findings hold implications for future structural design of diarylethene photochromic switches. PMID:23889496

Kudernac, Tibor; Kobayashi, Takao; Uyama, Ayaka; Uchida, Kingo; Nakamura, Shinichiro; Feringa, Ben L

2013-08-29

324

EDITORIAL: Molecular switches at surfaces Molecular switches at surfaces  

NASA Astrophysics Data System (ADS)

In nature, molecules exploit interaction with their environment to realize complex functionalities on the nanometer length scale. Physical, chemical and/or biological specificity is frequently achieved by the switching of molecules between microscopically different states. Paradigmatic examples are the energy production in proton pumps of bacteria or the signal conversion in human vision, which rely on switching molecules between different configurations or conformations by external stimuli. The remarkable reproducibility and unparalleled fatigue resistance of these natural processes makes it highly desirable to emulate nature and develop artificial systems with molecular functionalities. A promising avenue towards this goal is to anchor the molecular switches at surfaces, offering new pathways to control their functional properties, to apply electrical contacts, or to integrate switches into larger systems. Anchoring at surfaces allows one to access the full range from individual molecular switches to self-assembled monolayers of well-defined geometry and to customize the coupling between molecules and substrate or between adsorbed molecules. Progress in this field requires both synthesis and preparation of appropriate molecular systems and control over suitable external stimuli, such as light, heat, or electrical currents. To optimize switching and generate function, it is essential to unravel the geometric structure, the electronic properties and the dynamic interactions of the molecular switches on surfaces. This special section, Molecular Switches at Surfaces, collects 17 contributions describing different aspects of this research field. They analyze elementary processes, both in single molecules and in ensembles of molecules, which involve molecular switching and concomitant changes of optical, electronic, or magnetic properties. Two topical reviews summarize the current status, including both challenges and achievements in the field of molecular switches on metal surfaces, focusing on electronic and vibrational spectroscopy in one case and scanning tunneling microscopy studies in the other. Original research articles describe results in many aspects of the field, including: Self-assembly, self-organization, and controlled growth of molecular layers on various substrates. Highly-ordered arrays provide model systems with extraordinary structural properties, allowing one to adjust interactions between molecules and between molecule and substrate, and can be robustly prepared from solution, an essential prerequisite for applications. Conformational or electronic switching of molecules adsorbed at metal and semiconductor surfaces. These studies highlight the elementary processes governing molecular switching at surfaces as well as the wide range of possible stimuli. Carbon-based substrates such as graphene or carbon nanotubes. These substrates are attractive due to their effective two-dimensionality which implies that switching of adsorbed molecules can effect a significant back-action on the substrate. Mechanisms of conformational switching. Several contributions study the role of electron-vibron coupling and heating in current-induced conformational switching. We hope that the collection of articles presented here will stimulate and encourage researchers in surface physics and interfacial chemistry to contribute to the still emerging field of molecular switches at surfaces. We wish to acknowledge the support and input from many colleagues in preparing this special section. A significant part of this work has been conducted in the framework of the Sonderforschungsbereich 658 Elementary Processes in Molecular Switches at Surfaces of the Deutsche Forschungsgemeinschaft, to which we are grateful for financial support. Molecular surfaces at switches contents Molecular switches at surfacesMartin Weinelt and Felix von Oppen Optically and thermally induced molecular switching processes at metal surfacesPetra Tegeder Effects of electron-vibration coupling in transport through single moleculesKatharina J Franke and Jose Ignaci

Weinelt, Martin; von Oppen, Felix

2012-10-01

325

High current photoconductive semiconductor switches  

SciTech Connect

Photoconductive Semiconductor Switches (PCSS) are a completely different type of switch than those currently used in pulsed power applications. The most important attributes of PCSS are jitter-free triggering, low inductance, fast rise time, fast recovery (opening time), and high repetition rate. The most important limitation of the PCSS is the higher laser power required to activate them and the low-electric fields that they switch. These two issues are related because, for a given voltage that needs to be switched, a low field implies a large ''gap'' and, hence, a very large laser energy. This is especially troublesome since the laser energy required to reach a given switch resistance is proportional to the square of the gap spacing. In this paper we descibe major advances in PCSS. The first section describes how we are able to switch higher fields. Si can be used to switch fields of up to 82 kV/cm (a voltage of 123 kV across 1.5 cm), more than a factor of two higher than the 36 kV/cm that we reported a year ago. The development of PCSS for use in pulsed power application requires the ability to switch both high voltages and large currents. Having made signifcant progress in voltage standoff and switched fields, we are now concentrating on the current density issue. The second section describes the devlopment of two-impedance systems to test the maximum currents that the samples can switch. Presently the best we can switch corresponds to 4.0 kA (distributed over 2.1 cm) or 3.2 kA/cm (a current of 800 A distributed over a width of 0.25 cm) for GaAs in our sub-/OMEGA/ impedance test system. The third section focuses on the lock-on phenomenon first reported by our laboratory a year ago. 12 refs., 6 figs., 2 tabs.

Loubriel, G. M.; O'Malley, M. W.; Zutavern, F. J.; McKenzie, B. B.; Conley, W. R.; Hjalmarson, H. P.

1988-01-01

326

Study of optoelectronic switch for satellite-switched time-division multiple access  

NASA Technical Reports Server (NTRS)

The use of optoelectronic switching for satellite switched time division multiple access will improve the isolation and reduce the crosstalk of an IF switch matrix. The results are presented of a study on optoelectronic switching. Tasks include literature search, system requirements study, candidate switching architecture analysis, and switch model optimization. The results show that the power divided and crossbar switching architectures are good candidates for an IF switch matrix.

Su, Shing-Fong; Jou, Liz; Lenart, Joe

1987-01-01

327

TDP-43 toxicity in yeast.  

PubMed

The budding yeast Saccharomyces cerevisiae is an emerging tool for investigating the molecular pathways that underpin several human neurodegenerative disorders associated with protein misfolding. Amyotrophic lateral sclerosis (ALS) is a devastating adult onset neurodegenerative disease primarily affecting motor neurons. The protein TDP-43 has recently been demonstrated to play an important role in the disease, however, the mechanisms by which TDP-43 contributes to pathogenesis are unclear. To explore the mechanistic details that result in aberrant accumulation of TDP-43 and to discover potential strategies for therapeutic intervention, we employed a yeast TDP-43 proteinopathy model system. These studies allowed us to determine the regions of TDP-43 required for aggregation and toxicity and to define the effects of ALS-linked mutant forms of TDP-43. We have also been able to harness the power of yeast genetics to identify potent modifiers of TDP-43 toxicity using high-throughput yeast genetic screens. Here, we describe the methods and approaches that we have used in order to gain insight into TDP-43 biology and its role in disease. These approaches are readily adaptable to other neurodegenerative disease proteins. PMID:21115123

Armakola, Maria; Hart, Michael P; Gitler, Aaron D

2011-03-01

328

Yeast Proteomics and Protein Microarrays  

PubMed Central

Our understanding of biological processes as well as human diseases has improved greatly thanks to studies on model organisms such as yeast. The power of scientific approaches with yeast lies in its relatively simple genome, its facile classical and molecular genetics, as well as the evolutionary conservation of many basic biological mechanisms. However, even in this simple model organism, systems biology studies, especially proteomic studies had been an intimidating task. During the past decade, powerful high-throughput technologies in proteomic research have been developed for yeast including protein microarray technology. The protein microarray technology allows the interrogation of protein-protein, protein-DNA, protein-small molecule interaction networks as well as post-translational modification networks in a large-scale, high-throughput manner. With this technology, many groundbreaking findings have been established in studies with the budding yeast Saccharomyces cerevisiae, most of which could have been unachievable with traditional approaches. Discovery of these networks has profound impact on explicating biological processes with a proteomic point of view, which may lead to a better understanding of normal biological phenomena as well as various human diseases.

Chen, Rui; Snyder, Michael

2010-01-01

329

Maximising the yeast chronological lifespan.  

PubMed

When investigating aging it is important to focus on the factors that are needed to attain, and which can be manipulated to extend, the longest lifespans. This has long been appreciated by those workers who use Drosophila or Caenorhabditis elegans as model experimental systems to study aging. Often though it seems it is not a consideration in many studies of yeast chronological aging. In this chapter I summarise how recent work has revealed the preconditioning that is needed for yeast to survive for long periods in stationary phase, therefore for it to exhibit a long chronological life span (CLS). Of critical importance in this regard is the nature of the nutrient limitation that, during the earlier growth phase, had forced the cells to undergo growth arrest. I have attempted to highlight those studies that have focussed on the longest CLSs, as this helps to identify investigations that may be addressing - not just factors that can influence chronological longevity - but those factors that are correlated with the authentic processes of chronological aging. Attempting to maximize long-term stationary survival in yeast should also enhance the potential relevance of this organism as an aging model to those who wrestle with the problems of aging in more complex systems. Finally I also give a personal perspective of how studies on the yeast CLS may still yet provide some important new insights into events that are correlated with aging. PMID:22094421

Piper, Peter W

2012-01-01

330

Toxicogenomics using yeast DNA microarrays  

Microsoft Academic Search

Development of genomics and bioinformatics enable us to analyze the global gene expression profiles of cells by DNA microarray. Changes in gene expression patterns indicate changes in its physiological conditions. Following the exposure of an organism or cell to toxic chemicals or other environmental stresses, the global genetic responses can be expeditiously and easily analyzed. Baker's yeast, Saccharomyces cerevisiae, is

Daisuke Yasokawa; Hitoshi Iwahashi

2010-01-01

331

Dielectric properties of yeast cells  

Microsoft Academic Search

Summary Dielectric measurements were made on suspensions of intact yeast cells over a frequency range of 10 kHz to 100 MHz. The suspensions showed typical dielectric dispersions, which are considered to be caused by the presence of cytoplasmic membranes with sufficiently low conductivity. Since the conductivity of the cell wall was found to be of nearly the same value as

Koji Asami; Tetsuya Hanai; Naokazu Koizumi

1976-01-01

332

Emerging technologies in yeast genomics  

Microsoft Academic Search

The genomic revolution is undeniable: in the past year alone, the term 'genomics' was found in nearly 500 research articles, and at least 6 journals are devoted solely to genomic biology. More than just a buzzword, molecular biology has genuinely embraced genomics (the systematic, large-scale study of genomes and their functions). With its facile genetics, the budding yeast Saccharomyces cerevisiae

Anuj Kumar; Michael Snyder

2001-01-01

333

Bistable solitons and optical switching  

Microsoft Academic Search

Using a particular nonlinearity (the 'linear + smooth step' model) as an illustrative example, it is demonstrated numerically that cyclic switching between bistable soliton states of the highly-nonlinear (generalized) Schroedinger equation can occur. Some important aspects of the switching process, including the nature and role of the intermediate states, are discussed. This numerical simulation may serve as a model of

Richard H. Enns; Sadanand S. Rangnekar

1987-01-01

334

IP switching and gigabit routers  

Microsoft Academic Search

To cope with the growth in the Internet and corporate IP networks, we require IP routers capable of much higher performance than is possible with existing architectures. This article examines two approaches to the design of a high-performance router, the gigabit router and the IP switch, and then provides some detail on the implementation of an IP switch and the

P. Newman; G. Minshall; T. Lyon; L. Huston

1997-01-01

335

Broadband Latching Switches and Circulators.  

National Technical Information Service (NTIS)

Work during this period was concentrated on reducing the switching energy of the 1.0 - 2.0 GHz and the 2.0 - 4.0 GHz latching circulators. Several external return path configurations were developed to lower the switching energy while maintaining maximum b...

J. W. Simon W. K. Alverson J. E. Pippin J. K. Parks

1968-01-01

336

Battery switch for downhole tools  

SciTech Connect

An electrical circuit for a downhole tool may include a battery, a load electrically connected to the battery, and at least one switch electrically connected in series with the battery and to the load. The at least one switch may be configured to close when a tool temperature exceeds a selected temperature.

Boling, Brian E. (Sugar Land, TX)

2010-02-23

337

Vacuum Cut-off Switch.  

National Technical Information Service (NTIS)

The vacuum cut-off switch is shown in a system including an evacuation chamber, a pump, an electric motor, a battery and conduits connecting the components. A pressure responsive detecting device is associated with the switch for controlling the operation...

J. E. Coyle

1964-01-01

338

Ferroelectric Liquid Crystal Optical Interconnect Switching Systems.  

National Technical Information Service (NTIS)

This grant explored the possible use of ferroelectric liquid crystals (FLC's) in the reamization of photonic switching fabrics. Problems addressed included device fabrication, switch architectures, and switch performance. Experimental versions of most arc...

J. W. Goodman

1993-01-01

339

Alterable Magnetic Gratings for Fiber Optic Switching.  

National Technical Information Service (NTIS)

Optical mode switching of fiber light can enhance the capability of fiber optic communications systems by eliminating opto-electronic-opto converters at switching nodes and by performing the switching even on crosstalk-prone high data rate channels. Durin...

G. F. Sauter J. A. Krawczak G. L. Nelson F. G. Hewitt

1982-01-01

340

Affective modulation of attentional switching.  

PubMed

Affective modulation of attentional switching may have developed early in evolution and may therefore have primacy over other affective influences. This behavioral study investigated the influence of affect on attentional switching between emotionally neutral stimuli, whether limited-capacity control processes are involved, and whether attentional flexibility should be distinguished from attentional broadening. Experiment 1 showed that suboptimally presented happy faces facilitated switching from an automatized response routine, whereas angry faces had the opposite effect. In Experiment 2, participants with a dominant global (i.e., broad) or local (i.e., narrow) spatial bias switched more easily to the opposite bias after suboptimal happy faces than after neutral primes but less easily after angry faces. Affective modulation of attentional switching was probably incorporated during evolution in many more complex forms of information processing. PMID:23858953

Heerebout, Bram T; Todorovi?, Ana; Smedinga, Hilde E; Phaf, R Hans

2013-01-01

341

Optimized scalable network switch  

DOEpatents

In a massively parallel computing system having a plurality of nodes configured in m multi-dimensions, each node including a computing device, a method for routing packets towards their destination nodes is provided which includes generating at least one of a 2m plurality of compact bit vectors containing information derived from downstream nodes. A multilevel arbitration process in which downstream information stored in the compact vectors, such as link status information and fullness of downstream buffers, is used to determine a preferred direction and virtual channel for packet transmission. Preferred direction ranges are encoded and virtual channels are selected by examining the plurality of compact bit vectors. This dynamic routing method eliminates the necessity of routing tables, thus enhancing scalability of the switch.

Blumrich, Matthias A. (Ridgefield, CT) [Ridgefield, CT; Chen, Dong (Croton On Hudson, NY) [Croton On Hudson, NY; Coteus, Paul W. (Yorktown Heights, NY) [Yorktown Heights, NY; Gara, Alan G. (Mount Kisco, NY) [Mount Kisco, NY; Giampapa, Mark E. (Irvington, NY) [Irvington, NY; Heidelberger, Philip (Cortlandt Manor, NY) [Cortlandt Manor, NY; Steinmacher-Burow, Burkhard D. (Mount Kisco, NY) [Mount Kisco, NY; Takken, Todd E. (Mount Kisco, NY) [Mount Kisco, NY; Vranas, Pavlos M. (Bedford Hills, NY) [Bedford Hills, NY

2007-12-04

342

High voltage coaxial switch  

DOEpatents

A coaxial high voltage, high current switch having a solid cylindrical cold cathode coaxially surrounded by a thin hollow cylindrical inner electrode and a larger hollow cylindrical outer electrode. A high voltage trigger between the cathode and the inner electrode causes electrons to be emitted from the cathode and flow to the inner electrode preferably through a vacuum. Some of the electrons penetrate the inner electrode and cause a volumetric discharge in the gas (which may be merely air) between the inner and outer electrodes. The discharge provides a low impedance path between a high voltage charge placed on the outer electrode and a load (which may be a high power laser) coupled to the inner electrode. For high repetition rate the gas between the inner and outer electrodes may be continuously exchanged or refreshed under pressure. 3 figs.

Rink, J.P.

1983-07-19

343

High voltage coaxial switch  

DOEpatents

A coaxial high voltage, high current switch having a solid cylindrical cold cathode coaxially surrounded by a thin hollow cylindrical inner electrode and a larger hollow cylindrical outer electrode. A high voltage trigger between the cathode and the inner electrode causes electrons to be emitted from the cathode and flow to the inner electrode preferably through a vacuum. Some of the electrons penetrate the inner electrode and cause a volumetric discharge in the gas (which may be merely air) between the inner and outer electrodes. The discharge provides a low impedance path between a high voltage charge placed on the outer electrode and a load (which may be a high power laser) coupled to the inner electrode. For high repetition rate the gas between the inner and outer electrodes may be continuously exchanged or refreshed under pressure.

Rink, John P. (Los Alamos, NM)

1983-07-19

344

"Smart" watchdog safety switch  

DOEpatents

A method and apparatus for monitoring a process having a periodic output so that the process equipment is not damaged in the event of a controller failure, comprising a low-pass and peak clipping filter, an event detector that generates an event pulse for each valid change in magnitude of the filtered periodic output, a timing pulse generator, a counter that increments upon receipt of any timing pulse and resets to zero on receipt of any event pulse, an alarm that alerts when the count reaches some preselected total count, and a set of relays that opens to stop power to process equipment. An interface module can be added to allow the switch to accept a variety of periodic output signals.

Kronberg, James W. (353 Church Rd., Beech Island, SC 29842)

1991-01-01

345

''Smart'' watchdog safety switch  

DOEpatents

A method and apparatus for monitoring a process having a periodic output so that the process equipment is not damaged in the event of a controller failure, comprising a low-pass and peak clipping filter, an event detector that generates an event pulse for each valid change in magnitude of the filtered periodic output, a timing pulse generator, a counter that increments upon receipt of any timing pulse and resets to zero on receipt of any event pulse, an alarm that alerts when the count reaches some preselected total count, and a set of relays that opens to stop power to process equipment. An interface module can be added to allow the switch to accept a variety of periodic output signals. 21 figures.

Kronberg, J.W.

1991-10-01

346

Quantum switches and circuits  

US Patent & Trademark Office Database

Quantum switches, referred to as trisistors, operate on the basis of interactions between two elementary particles (EP), such as photons, electrons, phonons, etc. A first EP is used as a control input to the trisistor and interacts with a second EP, thereby inducing a detectable state change in the second EP that determines the trisistor's output value. The physical property which determines the particular EP state could be, for example, polarization, spin direction or energy level. The trisistors are connected primarily in series rather than in parallel as in previous quantum computing devices. The trisistors can be combined to form various types of logic gates, circuits, and other computer components. To implement the changes of state of the trisistors, one preferred embodiment employs nonlinear optics using a thin section of crystal.

2004-11-16

347

Yeasts in an industrial malting ecosystem.  

PubMed

The malting ecosystem consists of two components: the germinating cereal grains and the complex microbial community. Yeasts and yeast-like fungi are an important part of this ecosystem, but the composition and the effects of this microbial group have been largely unknown. In this study we surveyed the development of yeasts and yeast-like fungi in four industrial scale malting processes. A total of 136 malting process samples were collected and examined for the presence of yeasts growing at 15, 25 and 37 degrees C. More than 700 colonies were isolated and characterized. The isolates were discriminated by PCR-fingerprinting with microsatellite primer (M13). Yeasts representing different fingerprint types were identified by sequence analysis of the D1/D2 domain of the 26S rRNA gene. Furthermore, identified yeasts were screened for the production of alpha-amylase, beta-glucanase, cellulase and xylanase. A numerous and diverse yeast community consisting of both ascomycetous (25) and basidiomycetous (18) species was detected in the various stages of the malting process. The most frequently isolated ascomycetous yeasts belonged to the genera Candida, Clavispora, Galactomyces, Hanseniaspora, Issatchenkia, Pichia, Saccharomyces and Williopsis and the basidiomycetous yeasts to Bulleromyces, Filobasidium, Cryptococcus, Rhodotorula, Sporobolomyces and Trichosporon. In addition, two ascomycetous yeast-like fungi (black yeasts) belonging to the genera Aureobasidium and Exophiala were commonly detected. Yeasts and yeast-like fungi produced extracellular hydrolytic enzymes with a potentially positive contribution to the malt enzyme spectrum. Knowledge of the microbial diversity provides a basis for microflora management and understanding of the role of microbes in the cereal germination process. PMID:16758169

Laitila, A; Wilhelmson, A; Kotaviita, E; Olkku, J; Home, S; Juvonen, R

2006-11-01

348

Global gene deletion analysis exploring yeast filamentous growth.  

PubMed

The dimorphic switch from a single-cell budding yeast to a filamentous form enables Saccharomyces cerevisiae to forage for nutrients and the opportunistic pathogen Candida albicans to invade human tissues and evade the immune system. We constructed a genome-wide set of targeted deletion alleles and introduced them into a filamentous S. cerevisiae strain, ?1278b. We identified genes involved in morphologically distinct forms of filamentation: haploid invasive growth, biofilm formation, and diploid pseudohyphal growth. Unique genes appear to underlie each program, but we also found core genes with general roles in filamentous growth, including MFG1 (YDL233w), whose product binds two morphogenetic transcription factors, Flo8 and Mss11, and functions as a critical transcriptional regulator of filamentous growth in both S. cerevisiae and C. albicans. PMID:22984072

Ryan, Owen; Shapiro, Rebecca S; Kurat, Christoph F; Mayhew, David; Baryshnikova, Anastasia; Chin, Brian; Lin, Zhen-Yuan; Cox, Michael J; Vizeacoumar, Frederick; Cheung, Doris; Bahr, Sondra; Tsui, Kyle; Tebbji, Faiza; Sellam, Adnane; Istel, Fabian; Schwarzmüller, Tobias; Reynolds, Todd B; Kuchler, Karl; Gifford, David K; Whiteway, Malcolm; Giaever, Guri; Nislow, Corey; Costanzo, Michael; Gingras, Anne-Claude; Mitra, Robi David; Andrews, Brenda; Fink, Gerald R; Cowen, Leah E; Boone, Charles

2012-09-14

349

Alarm toe switch. [Patent application  

DOEpatents

An alarm toe switch inserted within a shoe for energizing an alarm circuit in a covert manner includes an insole mounting pad into which a miniature reed switch is fixedly molded. An elongated slot perpendicular to the reed switch is formed in the bottom surface of the mounting pad. A permanent cylindrical magnet positioned in the forward portion of the slot with a diameter greater than the pad thickness causes a bump above the pad. A foam rubber block is also positioned in the slot rearwardly of the magnet and holds the magnet in normal inoperative relation. A non-magnetic support plate covers the slot and holds the magnet and foam rubber in the slot. The plate minimizes bending and frictional forces to improve movement of the magnet for reliable switch activation. The bump occupies the knuckle space beneath the big toe. When the big toe is scrunched rearwardly the magnet is moved within the slot relative to the reed switch, thus magnetically activating the switch. When toe pressure is released the foam rubber block forces the magnet back into normal inoperative position to deactivate the reed switch.

Ganyard, F.P.

1980-11-18

350

ARTICLES: Polymer passive Q switch  

NASA Astrophysics Data System (ADS)

A study was made of polymer passive Q switches made of polyurethane acrylate colored with a dithiobenzyl complex of nickel. These switches were designed for the use in YAG:Nd3+ lasers. The polymer employed in these switches was elastic in a wide range of temperatures (beginning from -30°C), it adhered well to glass surfaces of the optical grade, and had a high optical strength. The layer structure of these switches improved the transfer of heat from the polymer to the substrate, the thermal conductivity of which was higher, so that the switches could operate stably at radiation intensities up to 16 W/cm2 without any need to move the switch. The photochemical stability of the dye in polyurethane acrylate was 106 pulses at a given point. When the resonator length was reduced to 6 cm and the active element was YAG:Nd3+ , the duration of the single pulses generated using a passive Q switch of this type was ~0.5 nsec and the divergence did not exceed 1 mrad (the corresponding half-width of the beam in the near-field zone was 1.5 mm).

Bezrodny?, V. I.; Tikhonov, E. A.

1986-12-01

351

Symmetric cell division in pseudohyphae of the yeast Saccharomyces cerevisiae.  

PubMed Central

Laboratory strains of Saccharomyces cerevisiae are dimorphic; in response to nitrogen starvation they switch from a yeast form (YF) to a filamentous pseudohyphal (PH) form. Time-lapse video microscopy of dividing cells reveals that YF and PH cells differ in their cell cycles and budding polarity. The YF cell cycle is controlled at the G1/S transition by the cell-size checkpoint Start. YF cells divide asymmetrically, producing small daughters from full-sized mothers. As a result, mothers and daughters bud asynchronously. Mothers bud immediately but daughters grow in G1 until they achieve a critical cell size. By contrast, PH cells divide symmetrically, restricting mitosis until the bud grows to the size of the mother. Thus, mother and daughter bud synchronously in the next cycle, without a G1 delay before Start. YF and PH cells also exhibit distinct bud-site selection patterns. YF cells are bipolar, producing their second and subsequent buds at either pole. PH cells are unipolar, producing their second and subsequent buds only from the end opposite the junction with their mother. We propose that in PH cells a G2 cell-size checkpoint delays mitosis until bud size reaches that of the mother cell. We conclude that yeast and PH forms are distinct cell types each with a unique cell cycle, budding pattern, and cell shape. Images

Kron, S J; Styles, C A; Fink, G R

1994-01-01

352

When yeast cells meet, karyogamy!  

PubMed Central

Cytoskeleton-mediated transport processes are central to the subcellular organization of cells. The nucleus constitutes the largest organelle of a cell, and studying how it is positioned and moved around during various types of cell morphogenetic processes has puzzled researchers for a long time. Now, the molecular architectures of the underlying dynamic processes start to reveal their secrets.   In yeast, karyogamy denotes the migration of two nuclei toward each other—termed nuclear congression—upon partner cell mating and the subsequent fusion of these nuclei to form a diploid nucleus. It constitutes a well-studied case. Recent insights completed the picture about the molecular processes involved and provided us with a comprehensive model amenable to quantitative computational simulation of the process. This review discusses our understanding of yeast nuclear congression and karyogamy and seeks to explain how a detailed, quantitative and systemic understanding has emerged from this knowledge.

Gibeaux, Romain; Knop, Michael

2013-01-01

353

Preparation of extracts from yeast.  

PubMed

Because yeast is exceptionally well suited to genetic analysis, both classical and molecular, it is an attractive system for expressing recombinant animal proteins for purification purposes. Methods available for lysing yeast cells include autolysis, pressure cells (e.g., French press), abrasives (glass bead vortexing), and enzymatic lysis (e.g., zymolase). One of the simplest methods, discussed in this protocol, involves the abrasive action of well-agitated glass beads. This is a very effective method for both low volumes (e.g., <1 mL using a microcentrifuge tube) and many liters using a specialized DynoMill apparatus. Cell breakage is typically >95%, as assessed by phase-contrast microscopy. PMID:21205845

Simpson, Richard J

2011-01-01

354

Switching performance of Nb3Sn persistent current switch  

NASA Astrophysics Data System (ADS)

We designed a persistent current switch consisting of Nb3Sn superconducting wire for Superconducting Magneto-Hydro-Dynamic Propulsion Ship (MHDS). Nb3Sn has Tc higher than NbTi, which is commonly used for the conventional persistent current switch, and thus is expected to show a higher stability against the disturbance. We therefore performed numerical simulations for the heat transfer in a 10kA-class Nb3Sn persistent current switch by using a finite element method. The results of switching performance will be presented based on the computer simulation for temperature distribution during the heating and cooling cycle. We also present the estimated time for the transition from the superconducting to normal state (off-state) and vice versa (on-state).

Tomita, M.; Nemoto, K.; Sugawara, K.; Murakami, M.

355

Flipping the switch: integrin switching provides metastatic competence.  

PubMed

Integrin switching plays a critical role in the progression to metastatic disease, but the mechanism by which it contributes remains poorly understood. In the 11 February 2014 issue of Science Signaling, Truong et al. identified a transforming growth factor-?-mediated, prometastatic switch that is activated by ?1 integrin inhibition in triple-negative breast cancers (TNBCs). Their work provides insight into the complex signaling changes that arise from integrin switching. Further characterization of ?-integrin switching will require elucidation of the distribution of specific ?-? integrin heterodimers and the role of ligand binding. Identifying the nature of the molecular interactions and the influence of a specific oncogenic context, including the status of driver mutations such as those in Myc and p53, will define the next phase in integrin cancer biology. PMID:24667375

Madamanchi, Aasakiran; Zijlstra, Andries; Zutter, Mary M

2014-03-25

356

Okazaki Fragment Maturation in Yeast  

Microsoft Academic Search

In the presence of proliferating cell nuclear antigen, yeast DNA polymerase (Pol ) replicated DNA at a rate of 40 - 60 nt\\/s. When downstream double-stranded DNA was encountered, Pol paused, but most replication complexes proceeded to carry out strand-displacement synthesis at a rate of 1.5 nt\\/s. In the presence of the flap endonuclease FEN1 (Rad27), the complex carried out

Rao Ayyagari; Xavier V. Gomes; Dmitry A. Gordenin; Peter M. J. Burgers

2003-01-01

357

Bistable solitons and optical switching  

NASA Astrophysics Data System (ADS)

Using a particular nonlinearity (the 'linear + smooth step' model) as an illustrative example, it is demonstrated numerically that cyclic switching between bistable soliton states of the highly-nonlinear (generalized) Schroedinger equation can occur. Some important aspects of the switching process, including the nature and role of the intermediate states, are discussed. This numerical simulation may serve as a model of optical switching between distinctly different soliton states in a nonlinear optical fiber and should simulate the search for the materials and mechanisms with appropriate nonlinearities.

Enns, Richard H.; Rangnekar, Sadanand S.

1987-07-01

358

Switching performance of Nb3Sn persistent current switch  

Microsoft Academic Search

We designed a persistent current switch consisting of Nb3Sn superconducting wire for Superconducting Magneto-Hydro-Dynamic Propulsion Ship (MHDS). Nb3Sn has Tc higher than NbTi, which is commonly used for the conventional persistent current switch, and thus is expected to show a higher stability against the disturbance. We therefore performed numerical simulations for the heat transfer in a 10kA-class Nb3Sn persistent current

M. Tomita; K. Nemoto; K. Sugawara; M. Murakami

2000-01-01

359

Techniques for optical packet switching and optical burst switching  

Microsoft Academic Search

Wavelength-division multiplexing appears to be the solution of choice for providing a faster networking infrastructure that can meet the explosive growth of the Internet. Several differ-ent technologies have been developed so far for the transfer of data over WDM. In this article we survey two new technologies which are still in the experimental stage, optical packet switch-ing and optical burst

Lisong Xu; H. G. Perros; G. Rouskas

2001-01-01

360

Zero background yeast reporter plasmids.  

PubMed

UAS-less reporter plasmids are widespread and powerful tools for the identification and analysis of binding sites for transcriptional activators. The common reporter plasmids for the yeast Saccharomyces cerevisiae are multicopy (2mu) vectors with the CYC1 core promoter upstream of the lacZ gene. Insertion of putative or known activator binding sites upstream of the core promoter puts lacZ (beta-galactosidase) expression under the control of the corresponding activator. Although these constructs have proved to work well for most purposes, they have certain limitations: (1) they give significant and carbon-source-dependent lacZ background expression; (2) unlike most other yeast promoters, the CYC1 upstream region has a partially open chromatin structure with an accessible TATA box; (3) they use only a single, moderately sensitive reporter; and (4) the use of multicopy vectors can result in activator titration. Here, we introduce novel reporter plasmids based on the yeast MEL1 (alpha-galactosidase) gene that can overcome all of these limitations. It is also shown that background expression is due to fortuitous activator binding sites within the plasmid backbones that are insufficiently shielded from the core promoters in the common CYC1 reporter plasmids. PMID:10773444

Melcher, K; Sharma, B; Ding, W V; Nolden, M

2000-04-18

361

Pheromone Signaling Pathways in Yeast  

NSDL National Science Digital Library

The actions of many extracellular stimuli are elicited by complexes of cell surface receptors, heterotrimeric guanine nucleotide–binding proteins (G proteins), and mitogen-activated protein kinase (MAPK) complexes. Analysis of haploid yeast cells and their response to peptide mating pheromones has produced important advances in the understanding of G protein and MAPK signaling mechanisms. Many of the components, their interrelationships, and their regulators were first identified in yeast. Examples include definitive demonstration of a positive signaling role for G protein βγ subunits, the discovery of a three-tiered structure of the MAPK module, development of the concept of a kinase-scaffold protein, and the discovery of the first regulator of G protein signaling protein. New and powerful genomic, proteomic, and computational approaches available in yeast are beginning to uncover new pathway components and interactions and have revealed their presence in unexpected locations within the cell. This updated Connections Map in the Database of Cell Signaling includes several major revisions to this prototypical signal response pathway.

Henrik G. Dohlman (University of North Carolina;Department of Biochemistry and Biophysics REV); Janna E. Slessareva (University of North Carolina;Department of Biochemistry and Biophysics REV)

2006-12-05

362

49 CFR 236.342 - Switch circuit controller.  

Code of Federal Regulations, 2013 CFR

...342 Switch circuit controller. Switch circuit controller connected at the point to switch, derail, or movable-point frog, shall be maintained so that its contacts will not be in position corresponding to switch point closure when switch point...

2013-10-01

363

Compact optical crossbar switch  

US Patent & Trademark Office Database

A planar optical crossbar switch comprising two thin planar substrates, on each of which are recorded or attached two holographic lenses between which light propagates by means of total internal reflection. The first lens is a negative cylindrical lens, used to input the incident light signal to the substrate, and the second lens is a positive cylindrical lens. The two substrates are disposed at right angles to each other in such a way that the positive lenses are positioned one on top of the other with a spatial light modulator sandwiched between them or beneath them. A linear array of detectors collects the output signal from the negative lens on the second substrate. Light from an element in the linear array of sources is spread out, by means of the negative cylindrical holographic lens on the first substrate, across a row of the SLM, and light from a column of the SLM is focused by means of the cylindrical holographic lenses on the second substrate, onto a particular element of the linear array of output detectors. To connect a signal form the ith source in the input array to the jth detector in the output array, the value of the {i,j} pixel of the SLM matrix should be in the ON state.

2001-01-09

364

Heteroleptic Copper Switches  

PubMed Central

Heteroleptic copper compounds have been designed and synthesized on solid supports. Chemical redox agents were used to change the oxidation state of the SiO2-immobilized heteroleptic copper compounds from Cu(I) to Cu(II) and then back to Cu(I). Optical spectroscopy of a dimethyl sulfoxide (DMSO) suspension demonstrated the reversibility of the Cu(I)/Cu(II) SiO2-immobilized compounds by monitoring the metal-to-ligand charge transfer (MLCT) peak at about 450 nm. EPR spectroscopy was used to monitor the isomerization of Cu(I) tetrahedral to Cu(II) square planar. This conformational change corresponds to a 90° rotation of one ligand with respect to the other. Conductive AFM (cAFM) and macroscopic gold electrodes were used to study the electrical properties of a p+ Si-immobilized heteroleptic copper compound where switching between the Cu(I)/Cu(II) states occurred at ?0.8 and +2.3 V.

Kabehie, Sanaz; Xue, Mei; Stieg, Adam Z.; Liong, Monty; Wang, Kang L.

2013-01-01

365

The magnetoelectrochemical switch.  

PubMed

In the field of spintronics, the archetype solid-state two-terminal device is the spin valve, where the resistance is controlled by the magnetization configuration. We show here how this concept of spin-dependent switch can be extended to magnetic electrodes in solution, by magnetic control of their chemical environment. Appropriate nanoscale design allows a huge enhancement of the magnetic force field experienced by paramagnetic molecular species in solutions, which changes between repulsive and attractive on changing the electrodes' magnetic orientations. Specifically, the field gradient force created within a sub-100-nm-sized nanogap separating two magnetic electrodes can be reversed by changing the orientation of the electrodes' magnetization relative to the current flowing between the electrodes. This can result in a breaking or making of an electric nanocontact, with a change of resistance by a factor of up to 10(3). The results reveal how an external field can impact chemical equilibrium in the vicinity of nanoscale magnetic circuits. PMID:25009179

Lunca Popa, Petru; Kemp, Neil T; Majjad, Hicham; Dalmas, Guillaume; Faramarzi, Vina; Andreas, Christian; Hertel, Riccardo; Doudin, Bernard

2014-07-22

366

Physiological properties of some yeast strains.  

PubMed

Twenty yeast strains have recently been isolated in pure cultures from natural and industrial sources and identified based mainly on physiological properties. The majority of the strains (15) are alcohologenic belonging to the genus Saccharomyces and comprise two brewer's (beer) yeast strains (S. carlsbergensis= S. uvarum A and B), two baker's yeast strains (S. cerevisiae CA and CP), one spirit yeast strain (S. cerevisiae CF) and ten wine yeast strains (S. cerevisiae var. ellipsoideus = S. ellipsoideus 1, 3, 4, 6, 8 and 9; S. oviformis 2, 5 and 7; and S. uvarum 10). The other 5 yeast strains belong to different species: Kloeckera apiculate, Candida mycoderma (Mycoderma vini), Pichia membranaefaciens, Rhodotorula glutinis and Torulopsis holmii, respectively. PMID:16841476

Oprean, Letitia; Gaspar, Enikö; Lengyel, Ecaterina; Cristea, V

2006-06-01

367

Yeasts Diversity in Fermented Foods and Beverages  

NASA Astrophysics Data System (ADS)

People across the world have learnt to culture and use the essential microorganisms for production of fermented foods and alcoholic beverages. A fermented food is produced either spontaneously or by adding mixed/pure starter culture(s). Yeasts are among the essential functional microorganisms encountered in many fermented foods, and are commercially used in production of baker's yeast, breads, wine, beer, cheese, etc. In Asia, moulds are predominant followed by amylolytic and alcohol-producing yeasts in the fermentation processes, whereas in Africa, Europe, Australia and America, fermented products are prepared exclusively using bacteria or bacteria-yeasts mixed cultures. This chapter would focus on the varieties of fermented foods and alcoholic beverages produced by yeasts, their microbiology and role in food fermentation, widely used commercial starters (pilot production, molecular aspects), production technology of some common commercial fermented foods and alcoholic beverages, toxicity and food safety using yeasts cultures and socio-economy

Tamang, Jyoti Prakash; Fleet, Graham H.

368

Metabolic engineering of malolactic wine yeast.  

PubMed

Malolactic fermentation is essential for the deacidification of high acid grape must. We have constructed a genetically stable industrial strain of Saccharomyces cerevisiae by integrating a linear cassette containing the Schizosaccharomyces pombe malate permease gene (mae1) and the Oenococcus oeni malolactic gene (mleA) under control of the S. cerevisiae PGK1 promoter and terminator sequences into the URA3 locus of an industrial wine yeast. The malolactic yeast strain, ML01, fully decarboxylated 5.5 g/l of malate in Chardonnay grape must during the alcoholic fermentation. Analysis of the phenotype, genotype, transcriptome, and proteome revealed that the ML01 yeast is substantially equivalent to the parental industrial wine yeast. The ML01 yeast enjoys 'Generally Regarded As Safe' status from the FDA and is the first genetically enhanced yeast that has been commercialized. Its application will prevent the formation of noxious biogenic amines produced by lactic acid bacteria in wine. PMID:16621641

Husnik, John I; Volschenk, Heinrich; Bauer, Jurgen; Colavizza, Didier; Luo, Zongli; van Vuuren, Hennie J J

2006-07-01

369

Electromagnetic Activation of Capillary Switches  

NASA Astrophysics Data System (ADS)

By designing coupled droplet pairs with the appropriate length scale to promote surface tension as the dominant force, one can create bi-stable capillary switches. This bi-stability can be triggered by pressure pulses, surface chemistry, electroosmosis, or body forces. To exploit the latter, we designed a capillary switch with electromagnetic activation. The resulting setup consists of a sub-millimeter tube, overfilled with a ferrofluid, surrounded by a wire coil to generate a magnetic field. Evidence of this capillary switching will be presented along with some theoretical basis in fluid- and electro-dynamics. The approach may also be used to investigate other transport phenomena in electromagnetically-coupled microfluidic systems, including the relative effects of translational motion of the ferrofluid (both particles and solvent molecules) versus the rotational effects of the individual magnetic grains. These individually addressable capillary switches offer intriguing applications including high-speed adaptive optics, actuators at the microscale, and possible PCB integration.

Malouin, Bernie; Dayal, Rohan; Parsa, Leila; Hirsa, Amir

2008-11-01

370

Switching characteristics of MINPN devices  

NASA Astrophysics Data System (ADS)

The I- V characteristics of the MINPN devices have been studied with the focus on the physical processes in the switchings. The study consists of computer simulation and experimental measurements, both of which show that these devices can exhibit one-state as well as two-state switchings. Such switchings are attributed to the regenerative process of the avalanche of the reverse PN junction with one or multiple current gains of the two composite NPN and MINP transistors. The MIS minority injection plays an important role in determining the switching characteristics of the device. Experimentally the breakover voltage and the hold-on voltage of this device are observed to be adjustable by applying base voltages. This can be considered as another evidence for the increased minority injection of the MIS structure.

Chang, David C. Y.; Lee, Chung Len; Lei, Tan Fu

1989-03-01

371

Theory of molecular hysteresis switch  

NASA Astrophysics Data System (ADS)

Molecular hysteresis switching has been recently observed in a series of experiments that measured the I-V spectrum of bipyridyl-dinitro oligophenylene-ethylene dithiol (BPDN) based molecular devices [1]. The experimental observations clearly show the presence of Coulomb blockade in single organic molecules that is responsible for the voltage-induced switching. We present the theory of the hysteresis switch which explains the non-linear hysteresis I-V characteristics based on the mechanisms of Coulomb blockade and the existence of two different molecular conformations of neutral and charged states of the molecule. [1] A.S. Blum, J.G. Kushmerick, D.P. Long, C.H. Patterson, J.C. Yang, J.C. Henderson, Y.X. Yao, J.M. Tour, R. Shashidhar, and B.R. Ratna, ``Molecularly inherent voltage-controlled conductance switching'' , Nature Materials 4, 167 (2005).

Kozhushner, Mortko; Oleynik, Ivan

2006-03-01

372

Optical interconnection networks for switching  

NASA Astrophysics Data System (ADS)

An ever-increasing bandwidth demand in computer communication and switching necessitates an efficient interconnection technology. Some of the advanced electronic parallel computer communication architectures may not even be sufficient to meet the ultra-high speed switching requirements of today's applications. The optical signal whether communicated through waveguides or free-space can propagate at the speed of light in the medium and, hence, is independent of the number of components that receive those signals. Optical interconnections are inherently fast, secure, and parallel in nature, which in turn, facilitate high bandwidth computer communication and switching. An attractive means for exploiting optical bema non-interaction property is to use free-space propagation but with focused, i.e., photorefractive volume holographic interconnection technique. In this talk we review a number of different optical interconnection network architectures with an emphasis on photorefractive volume holograms and their possibilities and problems as applied to computer communication switching.

Iftekharuddin, Khan M.

2001-07-01

373

IGBT: a solid state switch.  

National Technical Information Service (NTIS)

A Copper Vapour Laser Power Supply has been designed using a solid state switch consisting in eighteen Isolated Gate Bipolar Transistors (IGBT), -1200 volts, 400 Amps, each-in parallel. This paper presents the Isolated Gate Bipolar Transistor (IGBTs) repl...

D. Chatroux J. Maury B. Hennevin

1993-01-01

374

Method for Fingerprinting Yeast Cell Wall Mannans  

PubMed Central

Controlled acetolysis of yeast mannans yields mixtures of oligosaccharides with (1?2) and (1?3) linkages between the mannose units, whereas the less stable (1?6) linkages of the polysaccharide backbone are cleaved. The “fingerprints,” obtained by gel filtration of the oligosaccharide mixtures, can be used to distinguish between the different yeast mannans. The general method may be useful for determining the taxonomy of yeasts and for making correlations between immunochemical reactivity and mannan structure.

Kocourek, Jan; Ballou, Clinton E.

1969-01-01

375

Production of ethanol by immobilized yeast cells  

Microsoft Academic Search

Saccharomyces cerevisiae cells were immobilized in calcium alginate beads for use in the continuous production of ethanol. Yeasts were grown in medium supplemented with ethanol to selectively screen for a culture which showed the greatest tolerance to ethanol inhibition. Yeast beads were produced from a yeast slurry containing 1.5% alginate (w\\/v) which was added as drops to a 0.05M CaCl2

David Williams; Douglas M. Munnecke

1981-01-01

376

The yeast Golgi apparatus: insights and mysteries  

PubMed Central

The Golgi apparatus is known to modify and sort newly synthesized secretory proteins. However, fundamental mysteries remain about the structure, operation, and dynamics of this organelle. Important insights have emerged from studying the Golgi in yeasts. For example, yeasts have provided direct evidence for Golgi cisternal maturation, a mechanism that is likely to be broadly conserved. Here, we highlight features of the yeast Golgi as well as challenges that lie ahead.

Papanikou, Effrosyni; Glick, Benjamin S.

2009-01-01

377

Assembly of eukaryotic algal chromosomes in yeast  

PubMed Central

Background Synthetic genomic approaches offer unique opportunities to use powerful yeast and Escherichia coli genetic systems to assemble and modify chromosome-sized molecules before returning the modified DNA to the target host. For example, the entire 1 Mb Mycoplasma mycoides chromosome can be stably maintained and manipulated in yeast before being transplanted back into recipient cells. We have previously demonstrated that cloning in yeast of large (>?~?150 kb), high G?+?C (55%) prokaryotic DNA fragments was improved by addition of yeast replication origins every ~100 kb. Conversely, low G?+?C DNA is stable (up to at least 1.8 Mb) without adding supplemental yeast origins. It has not been previously tested whether addition of yeast replication origins similarly improves the yeast-based cloning of large (>150 kb) eukaryotic DNA with moderate G?+?C content. The model diatom Phaeodactylum tricornutum has an average G?+?C content of 48% and a 27.4 Mb genome sequence that has been assembled into chromosome-sized scaffolds making it an ideal test case for assembly and maintenance of eukaryotic chromosomes in yeast. Results We present a modified chromosome assembly technique in which eukaryotic chromosomes as large as ~500 kb can be assembled from cloned ~100 kb fragments. We used this technique to clone fragments spanning P. tricornutum chromosomes 25 and 26 and to assemble these fragments into single, chromosome-sized molecules. We found that addition of yeast replication origins improved the cloning, assembly, and maintenance of the large chromosomes in yeast. Furthermore, purification of the fragments to be assembled by electroelution greatly increased assembly efficiency. Conclusions Entire eukaryotic chromosomes can be successfully cloned, maintained, and manipulated in yeast. These results highlight the improvement in assembly and maintenance afforded by including yeast replication origins in eukaryotic DNA with moderate G?+?C content (48%). They also highlight the increased efficiency of assembly that can be achieved by purifying fragments before assembly.

2013-01-01

378

Single flux quantum crossbar switch  

Microsoft Academic Search

A crossbar switch has been designed using Single Flux Quantum (SFQ) gates exclusively for all internal functions. A 4×4 prototype has been fabricated in our Nb process foundry with Jc of 2000 A\\/cm2. We report on the design and performance of the switch and of an individual crosspoint element at high data rates (⩾1 Gbps). A novel design of a

Qing Ke; Bruce J. Dalrymple; Dale J. Durand; John W. Spargo

1997-01-01

379

High PRF high current switch  

DOEpatents

A triggerable, high voltage, high current, spark gap switch for use in pu power systems. The device comprises a pair of electrodes in a high pressure hydrogen environment that is triggered by introducing an arc between one electrode and a trigger pin. Unusually high repetition rates may be obtained by undervolting the switch, i.e., operating the trigger at voltages much below the self-breakdown voltage of the device.

Moran, Stuart L. (Fredericksburg, VA); Hutcherson, R. Kenneth (College Park, MD)

1990-03-27

380

Electroplated rf MEMS capacitive switches  

Microsoft Academic Search

RF microswitches are newly designed and fabricated with various structural geometry of transmission line, hinge, and movable plate formed by using electroplating techniques, low temperature processes, and dry releasing techniques. In particular, Strontium Titanate Oxide (SrTiO3) with high dielectric constant is investigated for high switching on\\/off ratio and on capacitance as a dielectric layer of a micromechanical capacitive switch. Achieved

Jae Y. Park; Geun H. Kim; Ki W. Chung; Jong U. Bu

2000-01-01

381

Conductance switching in organic monolayers  

Microsoft Academic Search

Self-assembled monolayers of some organic molecules, such as the bipyridyl-dinitro (BPDN) [1], present conductance switching (toggling between ON and OFF states). The switching happens upon crossing fixed threshold values in the applied bias voltage and the device can ``remember'' its previous state; thus, they have potential value as electronic memory devices. We use density-functional theory to elucidate the atomistic origins

Luis Agapito; Sabri Alkis; Jeffrey Krause; Hai-Ping Cheng

2009-01-01

382

Guaranteed Scheduling for Switches with Configuration Overhead  

Microsoft Academic Search

In this paper we present three algorithms that pro- vide performance guarantees for scheduling switches, such as op- tical switches, with configuration overhead. Each algorithm em- ulates an unconstrained (zero overhead) switch by accumulating a batch of configuration requests and generating a correspond- ing schedule for a constrained switch. Speedup is required both to cover the configuration overhead of the

Brian Towles; William J. Dally

2002-01-01

383

Switching activity estimation of CIC filter integrators  

Microsoft Academic Search

In this work, a method for estimation of the switching activity in integrators is presented. To achieve low power, it is always necessary to develop accurate and efficient methods to estimate the switching activity. The switching activities are then used to estimate the power consumption. In our work, the switching activity is first estimated for the general purpose integrators and

Muhammad Abbas; Oscar Gustafsson

2010-01-01

384

A Comparison of High-Voltage Switches  

Microsoft Academic Search

This report summarizes our work on high-voltage switches during the past few years. With joint funding from the Department of Energy (DOE) and the Department of Defense (DOD), we tested a wide variety of switches to a common standard. This approach permitted meaningful comparisons between disparate switches. Most switches were purchased from commercial sources, though some were experimental devices. For

K. W. Chu; G. L. Scott

1999-01-01

385

Characterizing and predicting search engine switching behavior  

Microsoft Academic Search

Search engine switching describes the voluntarily transition from one Web search engine to another. In this paper we present a study of search engine switching behavior that combines large- scale log-based analysis and survey data. We characterize aspects of switching behavior, and develop and evaluate predictive mod- els of switching behavior using features of the active query, the current session,

Ryen W. White; Susan T. Dumais

2009-01-01

386

Zero voltage switching approach for flyback converter  

Microsoft Academic Search

A zero voltage switched flyback power converter which realizes soft switching for every semiconductor is proposed. The sinusoidal resonant current flows through the secondary side rectifier diode and zero current switching of the diode is realized. Diode recovery is not generated. The proposed converter can operate with constant frequency pulse width modulation. High frequency switching and low noise are achieved

K. Yoshida; T. Ishii; N. Nagagata

1992-01-01

387

Research on control type soft switching converters  

Microsoft Academic Search

Paper clarifies the definition of control type soft switching and presents five characteristics for control type soft switching topologies. The theory of five characteristics is verified in the existing control type soft switching topologies, and a series of new control type soft switching topologies, such as buck, boost, buck-boost, cuk, zeta, sepic, flyback, and forward are constructed. A 200 kHz

Yilei Gu; Lijun Hang; Shijie Chen; Yu Du; Zhengyu Lu; Zhaoming Qian

2004-01-01

388

K-Band Latching Switches  

NASA Technical Reports Server (NTRS)

Design, development, and tests are described for two single-pole-double-throw latching waveguide ferrite switches: a K-band switch in WR-42 waveguide and a Ka-band switch in WR-28 waveguide. Both switches have structurally simple junctions, mechanically interlocked without the use of bonding materials; they are impervious to the effects of thermal, shock, and vibration stresses. Ferrite material for the Ka-band switch with a proper combination of magnetic and dielectric properties was available and resulted in excellent low loss, wideband performance. The high power handling requirement of the K-band switch limited the choice of ferrite to nickel-zinc compositions with adequate magnetic properties, but with too low relative dielectric constant. The relative dielectric constant determines the junction dimensions for given frequency responses. In this case the too low value unavoidably leads to a larger than optimum junction volume, increasing the insertion loss and restricting the operating bandwidth. Efforts to overcome the materials-related difficulties through the design of a composite junction with increased effective dielectric properties efforts to modify the relative dielectric constant of nickel-zinc ferrite are examined.

Piotrowski, W. S.; Raue, J. E.

1984-01-01

389

Origin of immunoglobulin isotype switching  

PubMed Central

Summary Background From humans to frogs, immunoglobulin class switching introduces different effector functions to antibodies through an intrachromsomal DNA recombination process at the heavy chain locus. Although there are two conventional antibody classes (IgM, IgW) in sharks, their heavy chains are encoded by 20 to >100 miniloci. These representatives of the earliest jawed vertebrates possess a primordial immunoglobulin gene organization where each gene cluster is autonomous and contains a few rearranging gene segments (VH-D1-D2-JH) with one constant region, ? or ?. Results V(D)J rearrangement always takes place within the ? cluster, but here we show that the VDJ can be expressed with constant regions from different clusters, although IgH genes are spatially distant, at >120 kb. Moreover, reciprocal exchanges take place between Ig? and Ig? genes. Switching is augmented with deliberate immunization and is concomitant with somatic hypermutation activity. Since switching occurs independently of the partners’ linkage position, some events involve transchromosomal recombination. The switch sites consist of direct joins between two genes in the 3? intron flanking JH. Conclusions Our data are consistent with a mechanism of cutting/joining of distal DNA lesions initiated by activation-induced cytidine deaminase (AID), in the absence of mammalian-type switch regions. We suggest that, in shark, with its many autonomous IgH targeted by programmed DNA breakage, factors predisposing broken DNA ends to translocate configured the earliest version of class switch recombination.

Zhu, Catherine; Lee, Victor; Finn, Alyssa; Senger, Kate; Zarrin, Ali A.; Pasquier, Louis Du; Hsu, Ellen

2012-01-01

390

6-azauracil sensitivity assay for yeast.  

PubMed

INTRODUCTIONTreatment of yeast with 6-Azauracil (6AU) leads to a reduction of intracellular GTP levels. The reduction in GTP levels is not itself lethal, but can block yeast growth when combined with mutations that affect transcriptional elongation. 6AU sensitivity thus can be used as a crude assay to test for mutations that affect transcriptional elongation. The assay described here requires growing saturated cultures of yeast, counting, and spotting serial dilutions of yeast on both CSM and CSM + 6AU plates. PMID:22484669

Tansey, William P

2006-01-01

391

Simplified techniques for identifying foodborne yeasts.  

PubMed

Four problematic areas associated with the identification of foodborne yeasts are discussed. These consist of (1) the inability of conventional identification tests to recognize some common and important foodborne yeasts characterized by genomic differences (e.g., Saccharomyces cerevisiae, S. bayanus and S. pastorianus); (2) the delay in application of non-traditional identification methods such as DNA fingerprinting, chromosome karyotyping, protein electrophoretic patterns and fatty acid profiles for routine identification purposes; (3) the lack of commercially available manual or automated identification systems dedicated to the diagnosis of foodborne yeasts; and (4) the disregard for considering ecological frequency of yeasts in computerized probabilistic identification systems. PMID:8357753

Deák, T

1993-06-25

392

Role of glucose signaling in yeast metabolism  

SciTech Connect

The conversion of glucose to ethanol and carbon dioxide by yeast was the first biochemical pathway to be studied in detail. The initial observation that this process is catalyzed by an extract of yeast led to the discovery of enzymes and coenzymes and laid the foundation for modern biochemistry. In this article, knowledge concerning the relation between uptake of and signaling by glucose in the yeast Saccharomyces cerevisiae is reviewed and compared to the analogous process in prokaryotes. It is concluded that (much) more fundamental knowledge concerning these processes is required before rational redesign of metabolic fluxes from glucose in yeast can be achieved.

Dam, K. van [Univ. of Amsterdam (Netherlands). E.C. Slater Inst.

1996-10-05

393

Evaluation of Automated Yeast Identification System  

NASA Technical Reports Server (NTRS)

One hundred and nine teleomorphic and anamorphic yeast isolates representing approximately 30 taxa were used to evaluate the accuracy of the Biolog yeast identification system. Isolates derived from nomenclatural types, environmental, and clinica isolates of known identity were tested in the Biolog system. Of the isolates tested, 81 were in the Biolog database. The system correctly identified 40, incorrectly identified 29, and was unable to identify 12. Of the 28 isolates not in the database, 18 were given names, whereas 10 were not. The Biolog yeast identification system is inadequate for the identification of yeasts originating from the environment during space program activities.

McGinnis, M. R.

1996-01-01

394

Electronic logic for enhanced switch reliability  

DOEpatents

A logic circuit is used to enhance redundant switch reliability. Two or more switches are monitored for logical high or low output. The output for the logic circuit produces a redundant and fail-safe representation of the switch outputs. When both switch outputs are high, the output is high. Similarly, when both switch outputs are low, the logic circuit's output is low. When the output states of the two switches do not agree, the circuit resolves the conflict by memorizing the last output state which both switches were simultaneously in and produces the logical complement of this output state. Thus, the logic circuit of the present invention allows the redundant switches to be treated as if they were in parallel when the switches are open and as if they were in series when the switches are closed. A failsafe system having maximum reliability is thereby produced.

Cooper, J.A.

1984-01-20

395

Architecture of IP switch based on optical crossbar switching network with feedback loops  

Microsoft Academic Search

This paper proposes a novel optical crossbar switching architecture. The proposed IP switch is based on an optical crossbar switching system, which take full use of advantages of electronics and photonics to face the challenge of the terabits per second IP switching. Group interconnect network is regarded as an ideal switching structure for its low blocking and excellent scalability. We

Xinjun Zhou; Mingcui Cao; Jiangdong Wu; Fengguang Luo; Jun Xu

2001-01-01

396

Influence of switching regimes on dielectric strength of high current triggered vacuum switches  

Microsoft Academic Search

Switching conditions influence on dielectric strength of internal insulation of high-current triggered vacuum switches with trapezoidal-rod electrode system is investigated. Investigations were carried out for two switching regimes. In the first regime electrode erosion occurs mainly in a vapor phase where the electrode surface remains smooth after switching. In the other switching regime a drop phase of electrode erosion prevails

V. A. Sidorov; D. F. Alferov; N. I. Korobova

1999-01-01

397

Optimized switching algorithm for synchronized switch damping for multimodal excitation  

NASA Astrophysics Data System (ADS)

Shunted piezoceramics can be used to dissipate vibration energy of a host structure and therefore reduce vibration amplitudes. The piezoceramic converts a portion of the mechanical energy into electric energy which is then dissipated in an electric network. One semi-active control technique is the synchronized switch damping on inductance (SSDI), which has a good damping performance and can adapt to a wide range of excitation frequencies. In the standard SSDI a switch is closed during maximum deformation for one half of the electrical period time. This results in an inversion of the electrical charge. For the rest of the half-period the switch is opened and the charge remains constant. This results in a nearly rectangular voltage signal, which is in antiphase with the deformation velocity. In case of multimodal excitation, more sophisticated switching laws are developed with the aim to extract vibration energy from higher modes (i.e. Richard). This paper describes a novel multimodal switching law for vibration damping. An observer is designed to obtain an estimation of the first two vibration modes, which are used to determine the switching times. In simulations the increase in energy dissipation is evaluated and compared to the standard SSDI technique. With the new switching algorithm an improvement in energy dissipation is observed. The theoretical results are validated by measurements carried out on a clamped-free beam. The location of the piezoceramics is chosen to optimize the electro-mechanical coupling with the first vibration mode of the beam. The modal observer is realized in a realtime environment. Measurements show a good agreement with the theoretical results.

Schwarzendahl, Sebastian M.; Han, Xu; Neubauer, Marcus; Wallaschek, Jörg

2010-03-01

398

Inverting ZCS Switched-Capacitor Bidirectional Converter  

Microsoft Academic Search

The proposed inverting type zero-current switching switched-capacitor (ZCS SC) DC\\/DC converters are a new type of bi-directional power flow control conversion schemes. They possess high efficiency, low EMI emission and current stress features for the proposed quasi-resonant switched-capacitor inverting converters. A family of inverting type zero-current switching switched-capacitor bi-directional converters is presented, which can improve the current stress problem during

Yaung-Shung Lee; Yin-Yuan Chiu; Ming-Wang Cheng

2006-01-01

399

Non-latching relay switch assembly  

DOEpatents

A non-latching relay switch assembly which includes a coil section and a switch or contact section. The coil section includes a permanent magnet and an electromagnet. The respective sections are arranged in separate locations or cavities in the assembly. The switch has a "normal" position and is selectively switched by an overriding electromagnetic assembly. The switch returns to the "normal" position when the overriding electromagnetic assembly is inactive.

Duimstra, Frederick A. (Anaheim Hills, CA)

1991-01-01

400

4 × 4 optical-gate matrix switch  

Microsoft Academic Search

An optical gate-based matrix switch is proposed and a switching function in a 4 × 4 experimental switch is demonstrated. The experimental switch is composed of fiber-type splitters, a lantham-modified lead zirconate-titanate solid solution (PLZT) optical-gate array, and fiber-type combiners. The switch has a broad bandwidth of 400 Mbit\\/s for nonreturn-to-zero (NRZ) optical signal transmission. A possible maximum matrix size

AKIRA HIMENO; MORIO KOBAYASHI

1985-01-01

401

Guided-wave optical gate matrix switch  

Microsoft Academic Search

An optical gate matrix switch that is made by integrating InGaAsP laser diode gates with high-silica guided-wave splitter and combiner circuits in a hybrid fashion is proposed and demonstrated. It provides point-to-multipoint switching. A preliminary experiment for a 4×4 matrix switch shows that the switch is capable of more than 400-Mb\\/s bandwidth signal switching

Akira Himeno; Hiroshi Terui; Morio Kobayashi

1988-01-01

402

Directional switching of the kinesin Cin8 through motor coupling.  

PubMed

Kinesin motor proteins are thought to move exclusively in either one or the other direction along microtubules. Proteins of the kinesin-5 family are tetrameric microtubule cross-linking motors important for cell division and differentiation in various organisms. Kinesin-5 motors are considered to be plus-end-directed. However, here we found that purified kinesin-5 Cin8 from budding yeast could behave as a bidirectional kinesin. On individual microtubules, single Cin8 motors were minus-end-directed motors, whereas they switched to plus-end-directed motility when working in a team of motors sliding antiparallel microtubules apart. This kinesin can thus change directionality of movement depending on whether it acts alone or in an ensemble. PMID:21350123

Roostalu, Johanna; Hentrich, Christian; Bieling, Peter; Telley, Ivo A; Schiebel, Elmar; Surrey, Thomas

2011-04-01

403

Drosophila Regulate Yeast Density and Increase Yeast Community Similarity in a Natural Substrate  

PubMed Central

Drosophila melanogaster adults and larvae, but especially larvae, had profound effects on the densities and community structure of yeasts that developed in banana fruits. Pieces of fruit exposed to adult female flies previously fed fly-conditioned bananas developed higher yeast densities than pieces of the same fruits that were not exposed to flies, supporting previous suggestions that adult Drosophila vector yeasts to new substrates. However, larvae alone had dramatic effects on yeast density and species composition. When yeast densities were compared in pieces of the same fruits assigned to different treatments, fruits that developed low yeast densities in the absence of flies developed significantly higher yeast densities when exposed to larvae. Across all of the fruits, larvae regulated yeast densities within narrow limits, as compared to a much wider range of yeast densities that developed in pieces of the same fruits not exposed to flies. Larvae also affected yeast species composition, dramatically reducing species diversity across fruits, reducing variation in yeast communities from one fruit to the next (beta diversity), and encouraging the consistent development of a yeast community composed of three species of yeast (Candida californica, C. zemplinina, and Pichia kluvyeri), all of which were palatable to larvae. Larvae excreted viable cells of these three yeast species in their fecal pools, and discouraged the growth of filamentous fungi, processes which may have contributed to their effects on the yeast communities in banana fruits. These and other findings suggest that D. melanogaster adults and their larval offspring together engage in ‘niche construction’, facilitating a predictable microbial environment in the fruit substrates in which the larvae live and develop.

Stamps, Judy A.; Yang, Louie H.; Morales, Vanessa M.; Boundy-Mills, Kyria L.

2012-01-01

404

YMDB: the Yeast Metabolome Database.  

PubMed

The Yeast Metabolome Database (YMDB, http://www.ymdb.ca) is a richly annotated 'metabolomic' database containing detailed information about the metabolome of Saccharomyces cerevisiae. Modeled closely after the Human Metabolome Database, the YMDB contains >2000 metabolites with links to 995 different genes/proteins, including enzymes and transporters. The information in YMDB has been gathered from hundreds of books, journal articles and electronic databases. In addition to its comprehensive literature-derived data, the YMDB also contains an extensive collection of experimental intracellular and extracellular metabolite concentration data compiled from detailed Mass Spectrometry (MS) and Nuclear Magnetic Resonance (NMR) metabolomic analyses performed in our lab. This is further supplemented with thousands of NMR and MS spectra collected on pure, reference yeast metabolites. Each metabolite entry in the YMDB contains an average of 80 separate data fields including comprehensive compound description, names and synonyms, structural information, physico-chemical data, reference NMR and MS spectra, intracellular/extracellular concentrations, growth conditions and substrates, pathway information, enzyme data, gene/protein sequence data, as well as numerous hyperlinks to images, references and other public databases. Extensive searching, relational querying and data browsing tools are also provided that support text, chemical structure, spectral, molecular weight and gene/protein sequence queries. Because of S. cervesiae's importance as a model organism for biologists and as a biofactory for industry, we believe this kind of database could have considerable appeal not only to metabolomics researchers, but also to yeast biologists, systems biologists, the industrial fermentation industry, as well as the beer, wine and spirit industry. PMID:22064855

Jewison, Timothy; Knox, Craig; Neveu, Vanessa; Djoumbou, Yannick; Guo, An Chi; Lee, Jacqueline; Liu, Philip; Mandal, Rupasri; Krishnamurthy, Ram; Sinelnikov, Igor; Wilson, Michael; Wishart, David S

2012-01-01

405

Cell size control in yeast  

PubMed Central

Cell size is an important adaptive trait that influences nearly all aspects of cellular physiology. Despite extensive characterization of the cell cycle regulatory network, the molecular mechanismscoupling growth to division, and thereby controlling cell size, have remained elusive. Recent workin yeast has reinvigorated the size control field and suggested provocative mechanisms forthe distinct functions of setting and sensing cell size. Further examination of size sensing models based on spatial gradients and molecular titration, coupled with elucidation of the pathways responsible for nutrient-modulated target size, may reveal the fundamental principles of eukaryotic cell size control.

Turner, Jonathan J.; Ewald, Jennifer C.; Skotheim, Jan M.

2012-01-01

406

Internet Switching by Satellite: An Ultra Fast Processor with Radio Burst Switching.  

National Technical Information Service (NTIS)

This paper introduces a new switching approach for satellites involved in routing statistical traffic, such as Internet Protocol (IP) data. Inherited from the optical domain, Radio Burst Switching (RBS) can combine a coarse switching granularity (such as ...

C. Haardt N. Couville

2005-01-01

407

High speed packet switching  

NASA Technical Reports Server (NTRS)

This document constitutes the final report prepared by Proteon, Inc. of Westborough, Massachusetts under contract NAS 5-30629 entitled High-Speed Packet Switching (SBIR 87-1, Phase 2) prepared for NASA-Greenbelt, Maryland. The primary goal of this research project is to use the results of the SBIR Phase 1 effort to develop a sound, expandable hardware and software router architecture capable of forwarding 25,000 packets per second through the router and passing 300 megabits per second on the router's internal busses. The work being delivered under this contract received its funding from three different sources: the SNIPE/RIG contract (Contract Number F30602-89-C-0014, CDRL Sequence Number A002), the SBIR contract, and Proteon. The SNIPE/RIG and SBIR contracts had many overlapping requirements, which allowed the research done under SNIPE/RIG to be applied to SBIR. Proteon funded all of the work to develop new router interfaces other than FDDI, in addition to funding the productization of the router itself. The router being delivered under SBIR will be a fully product-quality machine. The work done during this contract produced many significant findings and results, summarized here and explained in detail in later sections of this report. The SNIPE/RIG contract was completed. That contract had many overlapping requirements with the SBIR contract, and resulted in the successful demonstration and delivery of a high speed router. The development that took place during the SNIPE/RIG contract produced findings that included the choice of processor and an understanding of the issues surrounding inter processor communications in a multiprocessor environment. Many significant speed enhancements to the router software were made during that time. Under the SBIR contract (and with help from Proteon-funded work), it was found that a single processor router achieved a throughput significantly higher than originally anticipated. For this reason, a single processor router was developed and the final delivery under this contract will include a single processor CNX-500 router. The router and its interface boards (2 FDDIs and 2 dual-ethernets) are all product-quality components.

1991-01-01

408

Prevention of Yeast Spoilage in Feed and Food by the Yeast Mycocin HMK  

PubMed Central

The yeast Williopsis mrakii produces a mycocin or yeast killer toxin designated HMK; this toxin exhibits high thermal stability, high pH stability, and a broad spectrum of activity against other yeasts. We describe construction of a synthetic gene for mycocin HMK and heterologous expression of this toxin in Aspergillus niger. Mycocin HMK was fused to a glucoamylase protein carrier, which resulted in secretion of biologically active mycocin into the culture media. A partial purification protocol was developed, and a comparison with native W. mrakii mycocin showed that the heterologously expressed mycocin had similar physiological properties and an almost identical spectrum of biological activity against a number of yeasts isolated from silage and yoghurt. Two food and feed production systems prone to yeast spoilage were used as models to assess the ability of mycocin HMK to act as a biocontrol agent. The onset of aerobic spoilage in mature maize silage was delayed by application of A. niger mycocin HMK on opening because the toxin inhibited growth of the indigenous spoilage yeasts. This helped maintain both higher lactic acid levels and a lower pH. In yoghurt spiked with dairy spoilage yeasts, A. niger mycocin HMK was active at all of the storage temperatures tested at which yeast growth occurred, and there was no resurgence of resistant yeasts. The higher the yeast growth rate, the more effective the killing action of the mycocin. Thus, mycocin HMK has potential applications in controlling both silage spoilage and yoghurt spoilage caused by yeasts.

Lowes, K. F.; Shearman, C. A.; Payne, J.; MacKenzie, D.; Archer, D. B.; Merry, R. J.; Gasson, M. J.

2000-01-01

409

Fermentation studies using Saccharomyces diastaticus yeast strains  

SciTech Connect

The yeast species, Saccharomyces diastaticus, has the ability to ferment starch and dextrin, because of the extracellular enzyme, glucoamylase, which hydrolyzes the starch/dextrin to glucose. A number of nonallelic genes--DEX 1, DEX 2, and dextrinase B which is allelic to STA 3--have been isolated, which impart to the yeast the ability to ferment dextrin. Various diploid yeast strains were constructed, each being either heterozygous or homozygous for the individual dextrinase genes. Using 12 (sup 0) plato hopped wort (30% corn adjunct) under agitated conditions, the fermentation rates of the various diploid yeast strains were monitored. A gene-dosage effect was exhibited by yeast strains containing DEX 1 or DEX 2, however, not with yeast strains containing dextrinase B (STA 3). The fermentation and growth rates and extents were determined under static conditions at 14.4 C and 21 C. With all yeast strains containing the dextrinase genes, both fermentation and growth were increased at the higher incubation temperature. Using 30-liter fermentors, beer was produced with the various yeast strains containing the dextrinase genes and the physical and organoleptic characteristics of the products were determined. The concentration of glucose in the beer was found to increase during a 3-mo storage period at 21 C, indicating that the glucoamylase from Saccharomyces diastaticus is not inactivated by pasteurization. (Refs. 36).

Erratt, J.A.; Stewart, G.G.

1981-01-01

410

Characterization of wine yeasts for ethanol production  

Microsoft Academic Search

Selected wine yeasts were tested for their ethanol and sugar tolerance, and for their fermentative capacity. Growth (µ) and fermentation rates (?) were increasingly inhibited by increasing ethanol and glucose concentrations, “flor” yeasts being the least inhibited. Except in the latter strains, the ethanol production rate was accelerated by adding the glucose stepwise. The best fermenting strains selected in laboratory

Juan Jiménez; Tahía Benítez

1986-01-01

411

Characterization of wine yeasts for ethanol production  

Microsoft Academic Search

Summary Selected wine yeasts were tested for their ethanol and sugar tolerance, and for their fermentative capacity. Growth (µ) and fermentation rates (?) were increasingly inhibited by increasing ethanol and glucose concentrations, “flor” yeasts being the least inhibited. Except in the latter strains, the ethanol production rate was accelerated by adding the glucose stepwise. The best fermenting strains selected in

Juan Jiménez; Tahía Benítez

1986-01-01

412

Yeast Sporulation on Two Commonly Available Media.  

National Technical Information Service (NTIS)

In attempting to produce sporulation in some yeast strains, it was found that Trypticase Soy Broth (TSB; BBL) plus agar (1.5%) and Nutrient Agar (NA; BBL) induced fair to good sporulation of commercial bakers' yeast in 3 days, after two or three necessary...

W. P. Iverson

1967-01-01

413

On the origins of wine yeast  

Microsoft Academic Search

There is still a lack of agreement concerning the relative contribution of wine yeast that may originate in the vineyard compared to that which may originate in the cellar. Part of this controversy is due to the extreme difficulty of finding Saccharomyces cerevisiae on the grapes. We estimate that only about one in one-thousand grape berries carries wine yeast. However,

Robert Mortimer; Mario Polsinelli

1999-01-01

414

Yeasts are essential for cocoa bean fermentation.  

PubMed

Cocoa beans (Theobroma cacao) are the major raw material for chocolate production and fermentation of the beans is essential for the development of chocolate flavor precursors. In this study, a novel approach was used to determine the role of yeasts in cocoa fermentation and their contribution to chocolate quality. Cocoa bean fermentations were conducted with the addition of 200ppm Natamycin to inhibit the growth of yeasts, and the resultant microbial ecology and metabolism, bean chemistry and chocolate quality were compared with those of normal (control) fermentations. The yeasts Hanseniaspora guilliermondii, Pichia kudriavzevii and Kluyveromyces marxianus, the lactic acid bacteria Lactobacillus plantarum and Lactobacillus fermentum and the acetic acid bacteria Acetobacter pasteurianus and Gluconobacter frateurii were the major species found in the control fermentation. In fermentations with the presence of Natamycin, the same bacterial species grew but yeast growth was inhibited. Physical and chemical analyses showed that beans fermented without yeasts had increased shell content, lower production of ethanol, higher alcohols and esters throughout fermentation and lesser presence of pyrazines in the roasted product. Quality tests revealed that beans fermented without yeasts were purplish-violet in color and not fully brown, and chocolate prepared from these beans tasted more acid and lacked characteristic chocolate flavor. Beans fermented with yeast growth were fully brown in color and gave chocolate with typical characters which were clearly preferred by sensory panels. Our findings demonstrate that yeast growth and activity were essential for cocoa bean fermentation and the development of chocolate characteristics. PMID:24462702

Ho, Van Thi Thuy; Zhao, Jian; Fleet, Graham

2014-03-17

415

Oily yeasts as oleaginous cell factories.  

PubMed

Oily yeasts have been described to be able to accumulate lipids up to 20% of their cellular dry weight. These yeasts represent a minor proportion of the total yeast population, and only 5% of them have been reported as able to accumulate more than 25% of lipids. The oily yeast genera include Yarrowia, Candida, Rhodotorula, Rhodosporidium, Cryptococcus, Trichosporon, and Lipomyces. More specifically, examples of oleaginous yeasts include the species: Lipomyces starkeyi, Rhodosporidium toruloides, Rhodotorula glutinis, and Yarrowia lipolytica. Yeast do exhibit advantages for lipid production over other microbial sources, namely, their duplication times are usually lower than 1 h, are much less affected than plants by season or climate conditions, and their cultures are more easily scaled up than those of microalgae. Additionally, some oily yeasts have been reported to accumulate oil up to 80% of their dry weight and can indeed generate different lipids from different carbon sources or from lipids present in the culture media. Thus, they can vary their lipid composition by replacing the fatty acids present in their triglycerides. Due to the diversity of microorganisms and growth conditions, oily yeasts can be useful for the production of triglycerides, surfactants, or polyunsaturated fatty acids. PMID:21465305

Ageitos, Jose Manuel; Vallejo, Juan Andres; Veiga-Crespo, Patricia; Villa, Tomas G

2011-05-01

416

Can yeast transcriptomics help improve wine fermentation?  

Microsoft Academic Search

Wine fermentation is a dynamic and complex process in which the yeast cell is subjected to multiple stress conditions. A successful adaptation involves changes in gene expression profiles where a large number of genes are up- or down-regulated. Functional genomic approaches are com- monly used to obtain global gene expression profiles, providing a comprehensive view of yeast physiology. We used

C. Varela; J. Cárdenas; E. Agosin

417

Production of food and fodder yeasts.  

PubMed

A decade or so ago, there was considerable interest in developing single cell protein production from raw materials. Many factors have influenced the development of fodder yeast technology, notably the biochemistry and physiology of the yeast. It is shown that those considerations have led to the choice of a continuous fermentation technology. PMID:1733522

Boze, H; Moulin, G; Galzy, P

1992-01-01

418

CYGD: the Comprehensive Yeast Genome Database  

Microsoft Academic Search

The Comprehensive Yeast Genome Database (CYGD) compiles a comprehensive data resource for information on the cellular functions of the yeast Saccharomyces cerevisiae and related species, cho- sen as the best understood model organism for eukar- yotes. The database serves as a common resource generated by a European consortium, going beyond the provision of sequence information and functional annotations on individual

Ulrich Güldener; Martin Münsterkötter; Gabi Kastenmüller; Normann Strack; Jacques Van Helden; Christian Lemer; J. Richelles; Shoshana J. Wodak; J. García-martínez; J. E. Pérez-ortín; Holger Michael; Andreas Kaps; E. Talla; Bernard Dujon; B. André; J. L. Souciet; J. De Montigny; E. Bon; C. Gaillardin; Hans-werner Mewes

2005-01-01

419

Yeast: An Experimental Organism for Modern Biology.  

ERIC Educational Resources Information Center

Discusses the applicability and advantages of using yeasts as popular and ideal model systems for studying and understanding eukaryotic biology at the cellular and molecular levels. Cites experimental tractability and the cooperative tradition of the research community of yeast biologists as reasons for this success. (RT)

Botstein, David; Fink, Gerald R.

1988-01-01

420

Actively Q-switched fiber lasers: Switching dynamics and nonlinear processes  

Microsoft Academic Search

The Q-switching characteristics of actively Q-switched fiber lasers, especially the inconsistency of experimental observations with traditional Q-switching theory, are reviewed first in this paper. Based on a few typical high-power Q-switched rare-earth-doped fiber lasers, the switching dynamics in the linear and ring fiber cavities is then systematically illustrated under different fiber, pumping and switching conditions by using the traveling wave

Yong Wang; Chang-Qing Xu

2007-01-01

421

All-Optical Switch with Switch-Off Time Unrestricted by Carrier Lifetime  

Microsoft Academic Search

We propose a symmetric Mach-Zehnder-type all-optical switch which is based on the nonlinear refractive index change induced in semiconductors. Unlike most all-optical switches, the switch-off time, as well as the switch-on time, of this novel device is not limited by the usually slow carrier lifetime, allowing a very fast switching speed. Its switching characteristics are theoretically examined under various conditions.

Kazuhito Tajima

1993-01-01

422

High power solid state switches  

NASA Astrophysics Data System (ADS)

We have successfully produced an optically triggered thyristor based in Gallium Arsenide, developed a model for breakdown, and are developing two related devices, including a Gallium Arsenide based static inductor thyristor. We are getting at the basic limitations of Gallium Arsenide for these applications, and are developing models for the physical processes that will determine device limitations. The previously supported gas phase work - resulting in the back-lighted thyratron (BLT) - has actually resulted in a very changed view of how switching can be accomplished, and this is impacting the design of important machines. The BLT is being studied internationally: in Japan for laser fusion and laser isotope separation. ITT has built a BLT that has switched 30 kA at 60 kV in testing at NSWC Dahlgren and the device is being commercialized by another American company. Versions of the switch are now being tested for excimer laser and other applications. Basically, the switch, which arose from pulse power physics studies at USC, can switch more current faster (higher di/dt), with less housekeeping, and with other advantageous properties. There are a large number of other new applications, include kinetic energy weapons, pulsed microwave sources and R.F. accelerators.

Gundersen, Martin

1991-11-01

423

Binary switching in a 'symmetric' potential landscape  

PubMed Central

A binary switch is the basic building block for information processing. The potential energy profile of a bistable binary switch is a ‘symmetric' double well. The traditional method of switching it from one state (one well) to the other is to tilt the profile towards the desired state. Here, we present a case, where no such tilting is necessary to switch successfully, even in the presence of thermal noise. This happens because of the built-in dynamics inside the switch itself. It differs from the general perception on binary switching that in a ‘symmetric' potential landscape, the switching probability is 50% in the presence of thermal noise. Our results, considering the complete three-dimensional potential landscape, demonstrate intriguing phenomena on binary switching mechanism. With experimentally feasible parameters, we theoretically demonstrate such intriguing possibility in electric field induced magnetization switching of a shape-anisotropic single-domain magnetostrictive nanomagnet with two stable states at room-temperature.

Roy, Kuntal; Bandyopadhyay, Supriyo; Atulasimha, Jayasimha

2013-01-01

424

Binary switching in a 'symmetric' potential landscape.  

PubMed

A binary switch is the basic building block for information processing. The potential energy profile of a bistable binary switch is a 'symmetric' double well. The traditional method of switching it from one state (one well) to the other is to tilt the profile towards the desired state. Here, we present a case, where no such tilting is necessary to switch successfully, even in the presence of thermal noise. This happens because of the built-in dynamics inside the switch itself. It differs from the general perception on binary switching that in a 'symmetric' potential landscape, the switching probability is 50% in the presence of thermal noise. Our results, considering the complete three-dimensional potential landscape, demonstrate intriguing phenomena on binary switching mechanism. With experimentally feasible parameters, we theoretically demonstrate such intriguing possibility in electric field induced magnetization switching of a shape-anisotropic single-domain magnetostrictive nanomagnet with two stable states at room-temperature. PMID:24154561

Roy, Kuntal; Bandyopadhyay, Supriyo; Atulasimha, Jayasimha

2013-01-01

425

HOLLOTRON switch for megawatt lightweight space inverters  

NASA Technical Reports Server (NTRS)

The feasibility of satisfying the switching requirements for a megawatt ultralight inverter system using HOLLOTRON switch technology was determined. The existing experimental switch hardware was modified to investigate a coaxial HOLLOTRON switch configuration and the results were compared with those obtained for a modified linear HOLLOTRON configuration. It was concluded that scaling the HOLLOTRON switch to the current and voltage specifications required for a megawatt converter system is indeed feasible using a modified linear configuration. The experimental HOLLOTRON switch operated at parameters comparable to the scaled coaxial HOLLOTRON. However, the linear HOLLOTRON data verified the capability for meeting all the design objectives simultaneously including current density (greater than 2 A/sq cm), voltage (5 kV), switching frequency (20 kHz), switching time (300 ns), and forward voltage drop (less than or equal to 20 V). Scaling relations were determined and a preliminary design was completed for an engineering model linear HOLLOTRON switch to meet the megawatt converter system specifications.

Poeschel, R. L.; Goebel, D. M.; Schumacher, R. W.

1991-01-01

426

New search for pectolytic yeasts.  

PubMed

A new screening method for pectin-depolymerizing microorganisms is described. The method is based on precipitation of non-hydrolyzed citrus pectin with hexadecyltrimethylammonium bromide in a medium solidified with a bacterial gelling gum. A substrate depolymerized by the secreted enzymes does not precipitate, and the positive strains thus show transparent areas around the colonies. The method was used to screen 300 yeast and yeast-like microorganisms belonging to 52 different genera. The secretion of pectin-depolymerizing enzymes occurred with different frequencies in 13 genera (69 positive strains of 207 tested), the lowest frequency being found in the genus Candida (13 positive out of 125 strains tested) and the highest frequency in the genera Aureobasidium (4 of 6) Cryptococcus (29 of 38), Geotrichum (4 of 9), Kluyveromyces (5 of 5), Rhodosporidium (2 of 2), Leucosporidium (2 of 2), Trichosporon (3 of 6) and Ustilago (2 of 2). Strains giving the highest number of harvested cells after growth on pectin in a liquid medium have been identified. PMID:8549997

Biely, P; Sláviková, E

1994-01-01

427

Growing yeast into cylindrical colonies.  

PubMed

Microorganisms often form complex multicellular assemblies such as biofilms and colonies. Understanding the interplay between assembly expansion, metabolic yield, and nutrient diffusion within a freely growing colony remains a challenge. Most available data on microorganisms are from planktonic cultures, due to the lack of experimental tools to control the growth of multicellular assemblies. Here, we propose a method to constrain the growth of yeast colonies into simple geometric shapes such as cylinders. To this end, we designed a simple, versatile culture system to control the location of nutrient delivery below a growing colony. Under such culture conditions, yeast colonies grow vertically and only at the locations where nutrients are delivered. Colonies increase in height at a steady growth rate that is inversely proportional to the cylinder radius. We show that the vertical growth rate of cylindrical colonies is not defined by the single-cell division rate, but rather by the colony metabolic yield. This contrasts with cells in liquid culture, in which the single-cell division rate is the only parameter that defines the population growth rate. This method also provides a direct, simple method to estimate the metabolic yield of a colony. Our study further demonstrates the importance of the shape of colonies on setting their expansion. We anticipate that our approach will be a starting point for elaborate studies of the population dynamics, evolution, and ecology of microbial colonies in complex landscapes. PMID:24853750

Vulin, Clément; Di Meglio, Jean-Marc; Lindner, Ariel B; Daerr, Adrian; Murray, Andrew; Hersen, Pascal

2014-05-20

428

Antifungal resistance in yeast vaginitis.  

PubMed Central

The increased number of vaginal yeast infections in the past few years has been a disturbing trend, and the scientific community has been searching for its etiology. Several theories have been put forth to explain the apparent increase. First, the recent widespread availability of low-dosage, azole-based over-the-counter antifungal medications for vaginal yeast infections encourages women to self-diagnose and treat, and women may be misdiagnosing themselves. Their vaginitis may be caused by bacteria, parasites or may be a symptom of another underlying health condition. As a result, they may be unnecessarily and chronically expose themselves to antifungal medications and encourage fungal resistance. Second, medical technology has increased the life span of seriously immune compromised individuals, yet these individuals are frequently plagued by opportunistic fungal infections. Long-term and intense azole-based antifungal treatment has been linked to an increase in resistant Candida and non-Candida species. Thus, the future of limiting antifungal resistance lies in identifying the factors promoting resistance and implementing policies to prevent it.

Dun, E.

1999-01-01

429

Production of ethanol by immobilized yeast cells  

SciTech Connect

Saccharomyces cerevisiae cells were immobilized in calcium alginate beads for use in the continuous production of ethanol. Yeasts were grown in medium supplemented with ethanol to selectively screen for a culture which showed the greatest tolerance to ethanol inhibition. Yeast beads were produced from a yeast slurry containing 1.5% alginate (w/v) which was added as drops to a 0.05M CaCl2 solution. To determine their optimum fermentation parameters, ethanol production using glucose as a substrate was monitored in batch systems at varying physiological conditions (temperature,pH, ethanol concentration), cell densities, and gel concentrations. The data obtained were compared to optimum free cell ethanol fermentation parameters. The immobilized yeast cells were examined in a packed-bed reactor system operated under optimized parameters derived from batch-immobilized yeast cell experiments. Ethanol production rates, as well as residual sugar concentrations were monitored at different feedstock flow rates. (Refs. 13).

Williams, D.; Munnecke, D.M.

1981-08-01

430

Chromosomal structures of bottom fermenting yeasts.  

PubMed

A genomic comparison of bottom fermenting yeasts was performed by pulsed-field gel electrophoresis and Southern blot analysis with some S. cerevisiae gene probes. We confirmed that strains of bottom fermenting yeast have four chromosomes originating from S. bayanus. Since the structures of these chromosomes were recombined with S. cerevisiae chromosomes, these S. bayanus chromosomes could be differentiated from S. cerevisiae chromosomes using Southern hybridization. Our Southern hybridization results indicate that bottom fermenting yeasts have both chromosomes originating from both S. cerevisiae and S. bayanus. It was reconfirmed that top fermenting yeast should be classified as S. cerevisiae, based on the chromosomal structure. The chromosomal structure of S. pastorianus CBS1538, the type stain of S. pastorianus, was also investigated. This strain has chromosomes originating only from S. bayanus. S. carlsbergensis CBS1513 has chromosomes originating from both S. cerevisiae and S. bayanus. From these results, we contend that bottom fermenting yeasts should be classified as S. carlsbergensis. PMID:10553286

Yamagishi, H; Ogata, T

1999-09-01

431

Selection of antibody fragments by yeast display.  

PubMed

The critical need for renewable, high-quality affinity reagents in biological research, as well as for diagnostic and therapeutic applications, has required the development of new platforms of discovery. Yeast display is one of the main methods of in vitro display technology with phage display. Yeast display has been chosen by numerous groups to refine both affinity and specificity of antibodies because it enables fine discrimination between mutant clones of similar affinity. In addition, the construction of display libraries of antibody fragments in yeast permit to sample the immune antibody repertoire more fully than using phage. This chapter gives an updated overview of the available systems of yeast display platforms and libraries, followed up by technical descriptions of selection methods of antibody fragments by yeast display. PMID:22907357

Scholler, Nathalie

2012-01-01

432

System for automatically switching transformer coupled lines  

NASA Technical Reports Server (NTRS)

A system is presented for automatically controlling transformer coupled alternating current electric lines. The secondary winding of each transformer is provided with a center tap. A switching circuit is connected to the center taps of a pair of secondary windings and includes a switch controller. An impedance is connected between the center taps of the opposite pair of secondary windings. The switching circuit has continuity when the AC lines are continuous and discontinuity with any disconnect of the AC lines. Normally open switching means are provided in at least one AC line. The switch controller automatically opens the switching means when the AC lines become separated.

Dwinell, W. S. (inventor)

1979-01-01

433

The arterial switch operation before Jatene.  

PubMed

Attempts at the arterial switch operation predated the Senning and the Mustard venous switch procedures. No patients survived the earlier arterial switch methods. Therefore, from the 1960s to the 1980s, venous switch surgeries became the dominant treatment method for transposition of the great arteries. The Brazilian cardiac surgeon, Adib Jatene, reported the first successful arterial switch in 1975. The history of the earlier arterial switches performed in the 1950s and 1960s is not well known. This article discusses that early history. PMID:18709398

Evans, W N

2009-02-01

434

Pulsed power compression by plasma opening switch  

NASA Astrophysics Data System (ADS)

Inductive-energy-storage pulsed experiments using plasma opening switches have been carried out on a pulsed power generator (REIDEN IV-H). The plasma opening switch is an opening switch which operates on a nanosecond timescale. The experimental data show that the impedance of the switch increased up to 200 omega, a high voltage (6.4MV) and short pulse width (10nsec) output are obtained. The comparison between experimental data and analytic calculations indicates that the faster opening of the switch operation is obtained by increasing the plasma injection velocity and the self magnetic pressure effect mainly affects the final stage of the switch operation.

Yugami, N.; Miyamoto, S.; Fujita, H.; Ozaki, T.; Akiba, T.; Imasaki, K.; Nakai, S.; Yamanaka, C.

1985-10-01

435

Asp1, a Conserved 1/3 Inositol Polyphosphate Kinase, Regulates the Dimorphic Switch in Schizosaccharomyces pombe?  

PubMed Central

The ability to undergo dramatic morphological changes in response to extrinsic cues is conserved in fungi. We have used the model yeast Schizosaccharomyces pombe to determine which intracellular signal regulates the dimorphic switch from the single-cell yeast form to the filamentous invasive growth form. The S. pombe Asp1 protein, a member of the conserved Vip1 1/3 inositol polyphosphate kinase family, is a key regulator of the morphological switch via the cAMP protein kinase A (PKA) pathway. Lack of a functional Asp1 kinase domain abolishes invasive growth which is monopolar, while an increase in Asp1-generated inositol pyrophosphates (PP) increases the cellular response. Remarkably, the Asp1 kinase activity encoded by the N-terminal part of the protein is regulated negatively by the C-terminal domain of Asp1, which has homology to acid histidine phosphatases. Thus, the fine tuning of the cellular response to environmental cues is modulated by the same protein. As the Saccharomyces cerevisiae Asp1 ortholog is also required for the dimorphic switch in this yeast, we propose that Vip1