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At least 19 recordsLinked to original sources
PubMed1992

The yeast SFL2 gene may be necessary for mating-type control.

We previously reported the isolation of the yeast suppressor gene for flocculation, SFL2 (TUP1). SFL2 gene disruption results in pleiotropic phenotypes; the sfl2 null mutation also causes a morphological change similar to shmoo in both the MAT alpha and MATa/alpha cells. The MAT alpha and MATa/alpha sfl2 null mutant cells incorporate chitin into the new growth zone in the same way as the alpha-factor-treated MATa cells. In order to clarify the molecular basis of this morphological change, we examined the effect of the sfl2 null mutation on the mRNA production of various genes involved in mating-type control. The transcripts of both the STE2 (an a-specific gene) and STE3 (an alpha specific gene) genes are detected in the MAT alpha and MATa/alpha cells carrying the sfl2 null mutation. In addition, mRNA of the GPA1 gene (haploid-cell-specific gene) is also detected in the MATa/alpha sfl2 cells. However, there is no significant difference in the levels of the MAT alpha 2 and MATa1 transcripts. These results suggest that the SFL2 gene product may be necessary for alpha 2 and a1-alpha 2 repression.

Chitin↗
PubMed1992

Correlation of axenic linkage groups with the position of the microtubule-organizing center in aggregating Dictyostelium.

Positioning of the microtubule-organizing center (MTOC) in Dictyostelium discoideum was found to be genetically regulated. We examined the wild-type strain NC-4 cells independently maintained in different laboratories, freshly recovered cells from spores stocked for over 20 years, the temperature-sensitive growth mutant HU49 isolated from NC-4, as well as strain V-12 which is the opposite mating-type to NC-4. During aggregation on nonnutrient agar plates, all these strains showed similar cell polarity, as defined by the alignment of the nucleus ahead of the MTOC. By contrast, in Ax2 and Ax3, axenic strains carrying axenic mutations on linkage groups II and III, the MTOC was usually positioned ahead of the nucleus. Cells containing axenic linkage group II but not III positioned the MTOC ahead of the nucleus. Conversely cell polarity of strains including axenic linkage group III but not II was similar to that of wild-type cells. Thus axenic linkage group II, probably axeC or other linked gene(s) not yet identified, is responsible for the location of the MTOC anterior to the nucleus during aggregation. The anterior positioning of the MTOCs was prevented by growth on bacteria in cells carrying both axenic linkage groups, but not in those carrying only axenic linkage group II.

Animals↗
PubMed1992

Sexual development genes of Neurospora crassa.

The filamentous fungus Neurospora crassa undergoes a complex program of sexual development to form a fruiting body composed of several kinds of specialized tissue. Subtractive hybridization was used to isolate genes that are expressed preferentially during this sexual phase. Many such sexual development (sdv) genes were identified in a cosmid library of Neurospora genomic DNA. Fourteen of the sdv genes were subcloned, and their expression in mutant strains and under crossing and vegetative growth conditions was examined. All of the regulated transcripts were less abundant (and in many cases not detectable) in strains grown under vegetative (high nitrogen) conditions, suggesting that nitrogen starvation is required for their synthesis. The expression of most of the sdv genes also required a functional A mating type product, even under crossing growth conditions, suggesting that this product functions as a master control in sexual development. To determine if the products of the sdv genes play essential roles in the sexual cycle, a reverse-genetic approach (based on RIP (repeat-induced point mutation)-mediated gene disruptions) was used to create mutations in the genes. A mutant strain (asd-1) with a recessive crossing defect (apparently caused by the RIP process) was isolated; in this strain, early development is normal and may asci are formed, but ascospores are never delineated. A second recessive mutant strain (asd-2) was apparently created by ectopic integration of the transforming DNA into a gene required for the sexual process; in this strain the sexual process was blocked at an early stage, and the ascogeneous tissue underwent little development.

Cell Differentiation↗
PubMed1992

The protein sequence and some intron positions are conserved between the switching gene swi10 of Schizosaccharomyces pombe and the human excision repair gene ERCC1.

The switching gene swi10+ has a function in mating-type switching as well as in the repair of radiation damages. We have cloned the genomic swi10+ gene by functional complementation of the switching defect of the swi10-154 mutant. The swi10+ gene is not essential for viability. The DNA sequence revealed an open reading frame of 759 nucleotides interrupted by three introns of 127, 52 and 60 bp, respectively. The positions of intron I as well as of intron III of swi10 are evolutionary conserved in comparison to the introns III and IV of the human ERCC1 gene. The analysis of cDNA clones isolated by PCR amplification confirmed the structure of the swi10 gene. The putative Swi10 protein has homologies to the human and mouse ERCC1 protein, to Rad10 of Saccharomyces cerevisiae and to parts of UvrA and UvrC of E. coli. All these proteins are essential components for excision repair of damaged DNA. The Swi10 protein contains a putative DNA binding domain previously found in other proteins. Northern blot experiments and the analyses of cDNA clones indicate that intron I of the swi10 gene is not efficiently spliced.

Amino Acid Sequence↗
PubMed1991

Integrative transformation of the ascomycete Podospora anserina: identification of the mating-type locus on chromosome VII of electrophoretically separated chromosomes.

Protoplasts of wild-type strain s and a long-lived extrachromosomal mutant (AL2) of the ascomycete Podospora anserina were transformed using a plasmid (pAN7-1) which contains the hygromycin B phosphotransferase gene (hph) of Escherichia coli under the control of Aspergillus nidulans regulatory sequences. After optimizing the transformation procedure, transformation efficiencies of 15-21 transformants/micrograms plasmid DNA were obtained. Using a second selectable vector (pBT3), which contains the beta-tubuline gene of a benomyl-resistant Neurospora crassa mutant, the co-transformation rate was determined. Southern blot hybridization experiments revealed that the transforming plasmid became integrated into the genome of the recipient either as a single copy or as multiple copies. In addition, the data from molecular as well as from classical genetic analyses indicated that in independent transformants vector integration occurred at different positions. The mitotic and meiotic stability of transformants proved to be dependent on the number of integrated plasmid copies. Genetic analyses revealed a transformant in which the integrated vector is closely linked to the mating-type locus. Fractionation of whole chromosomes by pulsed field gel electrophoresis and subsequent hybridization of the immobilized DNAs against radiolabelled vector sequences indicated the largest of seven chromosomes as the chromosome containing the integrated vector and thus the mating-type locus.

Ascomycota↗
PubMedDate not supplied

The a and b loci of Ustilago maydis hybridize with DNA sequences from other smut fungi.

The smut fungi are obligately parasitic during the sexual phase of their life cycle, and the mating-type genes of these fungi play key roles in both sexual development and pathogenicity. Among species of smut fungi it is common to find a bipolar mating system in which one locus with two alternate alleles is believed to control cell fusion and establishment of the infectious cell type. Alternatively, several species have a tetrapolar mating system in which two different genetic loci, one of which has multiple alleles, control fusion and subsequent development of the infection hyphae. Cloned sequences from the a and b mating-type loci of the tetrapolar smut fungus Ustilago maydis were used as hybridization probes to DNAs from 23 different fungal strains, including smut fungi with both tetrapolar and bipolar mating systems. In general, all of the smut fungi hybridized with the mating-type genes from U. maydis, suggesting conservation of the sequences involved in mating interactions. A selection of DNAs from other ascomycete and basidiomycete fungi failed to hybridize with the U. maydis mating-type sequences. Exceptions to this finding include hybridization of DNA from the a1 idiomorph of U. maydis to DNA from one strain of U. violacea and hybridization of both a idiomorphs to DNA from Saccharomyces cerevisiae.

Genes, Fungal↗
PubMed1992

DNA damage induced mating type switching in Saccharomyces cerevisiae.

Haploid cells of the yeast Saccharomyces cerevisiae are able to undergo a differentiation-like process: they can switch their mating type between the a and the alpha state. The molecular mechanism of this interconversion of mating types is intrachromosomal gene conversion. It has been shown in a variety of studies that mating type switching in heterothallic strains can be induced by DNA damaging agents, and that different DNA damaging agents differ in the length of incubation after treatment required for induction. Because X-rays induce switching immediately after irradiation and because the DNA double-strand break repair pathway is required for switching, the event initiating heterothallic mating type switching is likely to be a DNA double-strand break. Therefore the assay for heterothallic mating type switching may screen for the induction of DNA double-strand breaks. Several aspects indicating a relationship of mating type switching to mechanisms associated with carcinogenesis are discussed.

DNA Damage↗
PubMed1992

The a mating type locus of U. maydis specifies cell signaling components.

The a mating type locus of the phytopathogenic fungus U. maydis controls fusion of haploid cells and filamentous growth of the dikaryotic mycelium. The a locus exists in two alleles, termed a1 and a2, which are defined by nonhomologous DNA regions comprising 4.5 kb for a1 and 8 kb for a2, flanked by identical sequences. Based on functional assays, mutants, and sequencing, we demonstrate that the mating type in each allele is determined by a set of two genes. One encodes a precursor for a lipopeptide mating factor, and the other specifies the receptor for the pheromone secreted by cells of opposite mating type. Thus, U. maydis employs a novel strategy to determine its mating type by providing the primary determinants of cell-cell recognition directly from the mating type locus.

Alleles↗
PubMed1992

Silencers, silencing, and heritable transcriptional states.

Three copies of the mating-type genes, which determine cell type, are found in the budding yeast Saccharomyces cerevisiae. The copy at the MAT locus is transcriptionally active, whereas identical copies of the mating-type genes at the HML and HMR loci are transcriptionally silent. Hence, HML and HMR, also known as the silent mating-type loci, are subject to a position effect. Regulatory sequences flank the silent mating-type loci and mediate repression of HML and HMR. These regulatory sequences are called silencers for their ability to repress the transcription of nearby genes in a distance- and orientation-independent fashion. In addition, a number of proteins, including the four SIR proteins, histone H4, and an alpha-acetyltransferase, are required for the complete repression of HML and HMR. Because alterations in the amino-terminal domain of histone H4 result in the derepression of the silent mating-type loci, the mechanism of repression may involve the assembly of a specific chromatin structure. A number of additional clues permit insight into the nature of repression at HML and HMR. First, an S phase event is required for the establishment of repression. Second, at least one gene appears to play a role in the establishment mechanism yet is not essential for the stable propagation of repression through many rounds of cell division. Third, certain aspects of repression are linked to aspects of replication. The silent mating-type loci share many similarities with heterochromatin. Furthermore, regions of S. cerevisiae chromosomes, such as telomeres, which are known to be heterochromatic in other organisms, require a subset of SIR proteins for repression. Further analysis of the transcriptional repression at the silent mating-type loci may lend insight into heritable repression in other eukaryotes.

Chromatin↗
PubMed1992

Developmental choices in mating-type interconversion in fission yeast.

Fission yeast cells follow a specific pattern of mating (cell) type switching in single cell pedigrees. Asymmetric cell divisions producing sisters of different developmental fates result from inheritance of specific parental DNA strands according to the classical model of semiconservative replication and segregation.

Gene Expression Regulation, Fungal↗
PubMed1992

The a locus governs cytoduction in Ustilago maydis.

We have developed a cytoduction assay to measure cell fusion quantitatively in the basidiomycete corn smut fungus Ustilago maydis. This assay employs a mutation conferring resistance to oligomycin that exhibits non-Mendelian inheritance and presumably affects the mitochondrial genome. After auxotrophic olir cells are mixed with prototrophic olis cells, prototrophic olir cells can be detected at a significant frequency after several hours of incubation, reaching a maximum of 10% of the total prototrophs in the mixture after 18 h. We demonstrate that this cell fusion event occurs only if the mating partners have different alleles of the a mating-type locus and is not influenced by the b locus. These studies support the view that the a locus but not the b locus controls establishment of the filamentous, pathogenic state.

Cell Fusion↗
PubMed1992

Ustilago maydis, the delightful blight.

Recent studies of the corn smut fungus life cycle and its regulation by two mating type loci and other genes provide a cornucopia of challenges in cell biology, genetics and protein structure. The fungus can exist in two states: nonpathogenic and pathogenic. The change from one state to the other is accompanied by a change in morphology (yeast-like to filamentous) and growth properties (saprophytic to parasitic).

Amino Acid Sequence↗
PubMed1992

Direct induction of tetraploids or homozygous diploids in the industrial yeast Saccharomyces cerevisiae by hydrostatic pressure.

Hydrostatic pressure and a dye plate method were used to investigate the direct induction of tetraploids or homozygous diploids from the industrial diploid or haploid yeast Saccharomyces cerevisiae. Above 200 MPa, hydrostatic pressure greatly inactivated the strains HF399s1 (alpha haploid), P-540 (a/alpha diploid), and P-544 (a/alpha diploid). At the same time, when pressure-treated cells of these strains were spread on a dye plate, some of the visible colonies were stained red/blue or dark blue (variant colonies); the rest stained violet, similar to colonies originating from diploid cells or haploid cells that were not pressure-treated. In addition, above 100 MPa, the formation of variant colonies increased with increasing pressure, and maximized (1 x 10(-1)) at 200 and 250 MPa, respectively. The size of almost all variant cells from P-544, P-540, and HF399s1 was visibly increased compared with that of untreated cells and the measured cellular DNA content of P-540 and HF399s1 was double that of untreated cells. Furthermore, based on random spore analysis and mass-matings, induced variants in the diploid strains were found to be tetraploid with an a/a/alpha/alpha genotype at the mating-type locus or, in the haploid strains, homozygous diploid with an alpha/alpha genotype. From these results we conclude that pressure treatment in combination with a dye plate is a useful method for strain improvement by direct induction of tetraploids or homozygous diploids from industrial strains whether diploid or haploid.

Crosses, Genetic↗
PubMed1992

XRS2, a DNA repair gene of Saccharomyces cerevisiae, is needed for meiotic recombination.

The XRS2 gene of Saccharomyces cerevisiae has been previously identified as a DNA repair gene. In this communication, we show that XRS2 also encodes an essential meiotic function. Spore inviability of xrs2 strains is rescued by a spo13 mutation, but meiotic recombination (both gene conversion and crossing over) is highly depressed in spo13 xrs2 diploids. The xrs2 mutation suppresses spore inviability of a spo13 rad52 strain suggesting that XRS2 acts prior to RAD52 in the meiotic recombination pathway. In agreement with the genetic data, meiosis-specific double-strand breaks at the ARG4 meiotic recombination hotspot are not detected in xrs2 strains. Despite its effects on meiotic recombination, the xrs2 mutation does not prevent mitotic recombination events, including homologous integration of linear DNA, mating-type switching and radiation-induced gene conversion. Moreover, xrs2 strains display a mitotic hyper-rec phenotype. Haploid xrs2 cells fail to carry out G2-repair of gamma-induced lesions, whereas xrs2 diploids are able to perform some diploid-specific repair of these lesions. Meiotic and mitotic phenotypes of xrs2 cells are very similar to those of rad50 cells suggesting that XRS2 is involved in homologous recombination in a way analogous to that of RAD50.

Crossing Over, Genetic↗
PubMed1992

Chromosome loss, hyperrecombination, and cell cycle arrest in a yeast mcm1 mutant.

The original mcm1-1 mutant was identified by its inability to propagate minichromosomes in an ARS-specific manner, suggesting that it is defective in the initiation of DNA synthesis at ARSs. This mutant is also defective in expression of alpha-mating-type-specific genes. Further genetic and biochemical studies confirmed that Mcm1 is a transcription factor that mediates the transcriptional regulation of a number of genes, including genes outside of the mating type complement, by interacting with different cofactors. Although MCM1 is an essential gene, none of the previously characterized mcm1 mutants exhibits significant growth defects. To assess which of the many roles of Mcm1 is essential for growth, we constructed and characterized a temperature-sensitive conditional mutant of mcm1, mcm1-110L. This mutant exhibits a temperature-dependent cell-cycle arrest, with a large, elongated bud and a single, undivided nucleus that has a DNA content of close to 2n. In addition, it shows elevated levels of chromosome loss and recombination. In spite of the severity of the mcm1-110L mutation, this mutant still retains an ARS-specific pattern of minichromosome instability. All of these phenotypes are precisely those exhibited by mutants in three MCM genes, MCM2, MCM3, and MCM5/CDC46, that have been shown to play interacting roles in the early steps of DNA replication.

Cell Cycle↗
PubMed1992

Isolation of Neurospora crassa A mating type mutants by repeat induced point (RIP) mutation.

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.

Alleles↗