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Relationships between a hyper-rec mutation (REM1) and other recombination and repair genes in yeast.Genetics May 1984Mutations in the REM1 gene of Saccharomyces cerevisiae confer a semidominant hyper-recombination and hypermutable phenotype upon mitotic cells ( GOLIN and ESPOSITO...
Mutations in the REM1 gene of Saccharomyces cerevisiae confer a semidominant hyper-recombination and hypermutable phenotype upon mitotic cells ( GOLIN and ESPOSITO 1977). These effects have not been observed in meiosis. We have examined the interactions of rem1 mutations with rad6-1, rad50 -1, rad52-1 or spo11 -1 mutations in order to understand the basis of the rem1 hyper-rec phenotype. The rad mutations have pleiotropic phenotypes; spo11 is only defective in sporulation and meiosis. The RAD6, RAD50 and SPO11 genes are not required for spontaneous mitotic recombination; mutations in the RAD52 gene cause a general spontaneous mitotic Rec- phenotype. Mutations in RAD50 , RAD52 or SPO11 eliminate meiotic recombination, and mutations in RAD6 prevent spore formation. Evidence for the involvement of RAD6 in meiotic recombination is less clear. Mutations in all three RAD genes confer sensitivity to X rays; the RAD6 gene is also required for UV damage repair. To test whether any of these functions might be involved in the hyper-rec phenotype conferred by rem1 mutations, double mutants were constructed. Double mutants of rem1 spo11 were viable and demonstrated rem1 levels of mitotic recombination, suggesting that the normal meiotic recombination system is not involved in producing the rem1 phenotype. The rem1 rad6 double mutant was also viable and had rem1 levels of mitotic recombination. Neither rem1 rad50 nor rem1 rad52 double mutants were viable. This suggests that rem1 causes its hyper-rec phenotype because it creates lesions in the DNA that are repaired using a recombination-repair system involving RAD50 and RAD52.
Topics: DNA Repair; Meiosis; Mutation; Recombination, Genetic; Saccharomyces cerevisiae
PubMed: 6373496
DOI: 10.1093/genetics/107.1.33 -
MBio 2011Genetic diversity is often generated during adaptation to stress, and in eukaryotes some of this diversity is thought to arise via recombination and reassortment of...
UNLABELLED
Genetic diversity is often generated during adaptation to stress, and in eukaryotes some of this diversity is thought to arise via recombination and reassortment of alleles during meiosis. Candida albicans, the most prevalent pathogen of humans, has no known meiotic cycle, and yet it is a heterozygous diploid that undergoes mitotic recombination during somatic growth. It has been shown that clinical isolates as well as strains passaged once through a mammalian host undergo increased levels of recombination. Here, we tested the hypothesis that stress conditions increase rates of mitotic recombination in C. albicans, which is measured as loss of heterozygosity (LOH) at specific loci. We show that LOH rates are elevated during in vitro exposure to oxidative stress, heat stress, and antifungal drugs. In addition, an increase in stress severity correlated well with increased LOH rates. LOH events can arise through local recombination, through homozygosis of longer tracts of chromosome arms, or by whole-chromosome homozygosis. Chromosome arm homozygosis was most prevalent in cultures grown under conventional lab conditions. Importantly, exposure to different stress conditions affected the levels of different types of LOH events, with oxidative stress causing increased recombination, while fluconazole and high temperature caused increases in events involving whole chromosomes. Thus, C. albicans generates increased amounts and different types of genetic diversity in response to a range of stress conditions, a process that we term "stress-induced LOH" that arises either by elevating rates of recombination and/or by increasing rates of chromosome missegregation.
IMPORTANCE
Stress-induced mutagenesis fuels the evolution of bacterial pathogens and is mainly driven by genetic changes via mitotic recombination. Little is known about this process in other organisms. Candida albicans, an opportunistic fungal pathogen, causes infections that require adaptation to different host environmental niches. We measured the rates of LOH and the types of LOH events that appeared in the absence and in the presence of physiologically relevant stresses and found that stress causes a significant increase in the rates of LOH and that this increase is proportional to the degree of stress. Furthermore, the types of LOH events that arose differed in a stress-dependent manner, indicating that eukaryotic cells generate increased genetic diversity in response to a range of stress conditions. We propose that this "stress-induced LOH" facilitates the rapid adaptation of C. albicans, which does not undergo meiosis, to changing environments within the host.
Topics: Antifungal Agents; Candida albicans; Hot Temperature; Loss of Heterozygosity; Mitosis; Oxidative Stress; Recombination, Genetic; Stress, Physiological
PubMed: 21791579
DOI: 10.1128/mBio.00129-11 -
Molecular Cell Dec 2010Holliday junction (HJ) resolution is required for segregation of chromosomes and for formation of crossovers during homologous recombination. The identity of the...
Holliday junction (HJ) resolution is required for segregation of chromosomes and for formation of crossovers during homologous recombination. The identity of the resolvase(s) that functions in vivo has yet to be established, although several proteins able to cut HJs in vitro have been identified as candidates in yeasts and mammals. Using an assay to detect unselected products of mitotic recombination, we found a significant decrease in crossovers in the Saccharomyces cerevisiae mus81Δ mutant. Yen1 serves a backup function responsible for resolving intermediates in mus81Δ mutants, or when conversion tracts are short. In the absence of both Mus81 and Yen1, intermediates are not channeled exclusively to noncrossover recombinants, but instead are processed by Pol32-dependent break-induced replication (BIR). The channeling of recombination from reciprocal exchange to BIR results in greatly increased spontaneous loss of heterozygosity (LOH) and chromosome mis-segregation in the mus81Δ yen1Δ mutant, typical of the genomic instability found in tumor cells.
Topics: DNA-Binding Proteins; Endonucleases; Genome, Fungal; Genomic Instability; Holliday Junction Resolvases; Mitosis; Mutation; Recombination, Genetic; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins
PubMed: 21172663
DOI: 10.1016/j.molcel.2010.11.016 -
Nature Jul 2006During meiosis, accurate separation of maternal and paternal chromosomes requires that they first be connected to one another through homologous recombination. Meiotic... (Review)
Review
During meiosis, accurate separation of maternal and paternal chromosomes requires that they first be connected to one another through homologous recombination. Meiotic recombination has many intriguing but poorly understood features that distinguish it from recombination in mitotically dividing cells, and several of these features depend on the meiosis-specific DNA strand exchange protein Dmc1 (disrupted meiotic cDNA1). Many questions about this protein have arisen since its discovery more than a decade ago, but recent genetic and biochemical breakthroughs promise to shed light on the unique behaviours and functions of this central player in the remarkable chromosome dynamics of meiosis.
Topics: Adenosine Triphosphatases; Animals; Cell Cycle Proteins; Crossing Over, Genetic; DNA; DNA-Binding Proteins; Humans; Meiosis; Models, Genetic; Sequence Homology, Nucleic Acid
PubMed: 16838012
DOI: 10.1038/nature04885 -
Genetics Dec 1989We have previously shown direct-repeat recombination events leading to loss of a plasmid integrated at the GAL10 locus in Saccharomyces cerevisiae are stimulated by...
We have previously shown direct-repeat recombination events leading to loss of a plasmid integrated at the GAL10 locus in Saccharomyces cerevisiae are stimulated by transcription of the region. We have examined the role of two recombination- and repair-defective mutations, rad1 and rad52, on direct repeat recombination in transcriptionally active and inactive sequences. We show that the RAD52 gene is required for transcription-stimulated recombination events leading to loss of the integrated plasmid. Similarly, Gal+ events between the duplicated repeats that retain the integrated plasmid DNA (Gal+ Ura+ replacement events) are reduced 20-fold in the rad52 mutant in sequences that are constitutively expressed. In contrast, in sequences that are not expressed, the rad52 mutation reduces plasmid loss events by only twofold and Gal+ Ura+ replacements by fourfold. We also observe an increase in disome-associated plasmid loss events in the rad52 mutant, indicative of chromosome gain. This event is not affected by expression of the region. Plasmid loss events in rad1 mutant strains are reduced only twofold in transcriptionally active sequences and are not affected in sequences that are repressed. However, the rad1 and rad52 double mutant shows a decrease in plasmid loss events greater than the sum of the decreases in the rates of this event displayed by either single mutant in both constitutive and repressed DNA, indicating a synergistic interaction between these two genes. The synergism is limited to recombination since the rad1 rad52 double mutant is no more sensitive when compared with either single mutant in its ability to survive radiation damage. Finally, the recombination pathway that remains in the double mutant is positively affected by transcription of the region.
Topics: DNA Repair; DNA, Fungal; Gamma Rays; Gene Conversion; Genes, Fungal; Recombination, Genetic; Restriction Mapping; Saccharomyces cerevisiae; Transcription, Genetic; Ultraviolet Rays
PubMed: 2693208
DOI: 10.1093/genetics/123.4.725 -
Proceedings of the National Academy of... Mar 2008Mitotic recombination between homologous chromosomes is a genetic technique for mosaic analysis in model organisms. The general application of this technique in the...
Mitotic recombination between homologous chromosomes is a genetic technique for mosaic analysis in model organisms. The general application of this technique in the mouse depends on establishment of effective recombination systems for individual chromosomes and reliable and sensitive methods for detection of recombination events. Here, we established a Cre/LoxP-mediated recombination system in mice for mosaic analysis of full-length chromosome 17. Cre-mediated germ-line recombination between the homologous chromosomes was observed with approximately 9% frequency in a progeny test. Mitotic recombination in somatic tissues was evaluated and scored in B and T lymphocytes with the aid of surface markers and fluorescent-activated cell sorting. We show that a lineage-specific Cre can induce mitotic recombination with a highly reproducible frequency of 0.5-1.0% in lymphoid progenitors. The recombination system established here allows for a simple and accurate detection and isolation of recombination events in live cells, making this system particularly attractive for mosaic analysis or mutagenesis studies in the immune system.
Topics: Alleles; Animals; Attachment Sites, Microbiological; Chromosomes, Mammalian; Female; Germ Cells; Integrases; Lymphocytes; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Mitosis; Recombination, Genetic; Sensitivity and Specificity
PubMed: 18326030
DOI: 10.1073/pnas.0800798105 -
Proceedings of the National Academy of... Jul 2018The chromosomes of many eukaryotes have regions of high GC content interspersed with regions of low GC content. In the yeast , high-GC regions are often associated with...
The chromosomes of many eukaryotes have regions of high GC content interspersed with regions of low GC content. In the yeast , high-GC regions are often associated with high levels of meiotic recombination. In this study, we constructed genes that differ substantially in their base composition [ (31% GC), (43% GC), and (63% GC)] but encode proteins with the same amino acid sequence. The strain with had an approximately sevenfold elevated rate of mutations compared with the strains with or About half of these mutations were single-base substitutions and were dependent on the error-prone DNA polymerase ζ. About 30% were deletions or duplications between short (5-10 base) direct repeats resulting from DNA polymerase slippage. The gene also had elevated rates of meiotic and mitotic recombination relative to the or genes. Thus, base composition has a substantial effect on the basic parameters of genome stability and evolution.
Topics: Base Composition; Base Sequence; Recombination, Genetic; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins; Sequence Deletion
PubMed: 29987035
DOI: 10.1073/pnas.1807334115 -
Proceedings of the National Academy of... Nov 2020Conventional models of genome evolution are centered around the principle that mutations form independently of each other and build up slowly over time. We characterized...
Conventional models of genome evolution are centered around the principle that mutations form independently of each other and build up slowly over time. We characterized the occurrence of bursts of genome-wide loss-of-heterozygosity (LOH) in , providing support for an additional nonindependent and faster mode of mutation accumulation. We initially characterized a yeast clone isolated for carrying an LOH event at a specific chromosome site, and surprisingly found that it also carried multiple unselected rearrangements elsewhere in its genome. Whole-genome analysis of over 100 additional clones selected for carrying primary LOH tracts revealed that they too contained unselected structural alterations more often than control clones obtained without any selection. We also measured the rates of coincident LOH at two different chromosomes and found that double LOH formed at rates 14- to 150-fold higher than expected if the two underlying single LOH events occurred independently of each other. These results were consistent across different strain backgrounds and in mutants incapable of entering meiosis. Our results indicate that a subset of mitotic cells within a population can experience discrete episodes of systemic genomic instability, when the entire genome becomes vulnerable and multiple chromosomal alterations can form over a narrow time window. They are reminiscent of early reports from the classic yeast genetics literature, as well as recent studies in humans, both in cancer and genomic disorder contexts. The experimental model we describe provides a system to further dissect the fundamental biological processes responsible for punctuated bursts of structural genomic variation.
Topics: Chromosomes, Fungal; Genome, Fungal; Genomic Instability; Loss of Heterozygosity; Mutation; Recombination, Genetic; Saccharomyces cerevisiae
PubMed: 33106418
DOI: 10.1073/pnas.2010303117 -
Molecular and Cellular Biology Oct 1981We have utilized the single equational meiotic division conferred by the spo13-1 mutation of Saccharomyces cerevisiae (S. Klapholtz and R. E. Esposito, Genetics...
We have utilized the single equational meiotic division conferred by the spo13-1 mutation of Saccharomyces cerevisiae (S. Klapholtz and R. E. Esposito, Genetics 96:589-611, 1980) as a technique to study the genetic control of meiotic recombination and to analyze the meiotic effects of several radiation-sensitive mutations (rad6-1, rad50-1, and rad52-1) which have been reported to reduce meiotic recombination (Game et al., Genetics 94:51-68, 1980); Prakash et al., Genetics 94:31-50, 1980). The spo13-1 mutation eliminates the meiosis I reductional segregation, but does not significantly affect other meiotic events (including recombination). Because of the unique meiosis it confers, the spo13-1 mutation provides an opportunity to recover viable meiotic products in a Rec- background. In contrast to the single rad50-1 mutant, we found that the double rad50-1 spo13-1 mutant produced viable ascospores after meiosis and sporulation. These spores were nonrecombinant: meiotic crossing-over was reduced at least 150-fold, and no increase in meiotic gene conversion was observed over mitotic background levels. The rad50-1 mutation did not, however, confer a Rec- phenotype in mitosis; rather, it increased both spontaneous crossing-over and gene conversion. The spore inviability conferred by the single rad6-1 and rad52-1 mutations was not eliminated by the presence of the spo13-1 mutation. Thus, only the rad50 gene has been unambiguously identified by analysis of viable meiotic ascospores as a component of the meiotic recombination system.
Topics: Crossing Over, Genetic; Genotype; Meiosis; Mitosis; Mutation; Phenotype; Recombination, Genetic; Saccharomyces cerevisiae; Spores, Fungal
PubMed: 7050657
DOI: 10.1128/mcb.1.10.891-901.1981 -
Nucleic Acids Research Dec 2019We have explored the meiotic roles of cohesin modulators Pds5 and Rad61/Wapl, in relation to one another, and to meiotic kleisin Rec8, for homolog pairing, all...
We have explored the meiotic roles of cohesin modulators Pds5 and Rad61/Wapl, in relation to one another, and to meiotic kleisin Rec8, for homolog pairing, all physically definable steps of recombination, prophase axis length and S-phase progression, in budding yeast. We show that Pds5 promotes early steps of recombination and thus homolog pairing, and also modulates axis length, with both effects independent of a sister chromatid. [Pds5+Rec8] promotes double-strand break formation, maintains homolog bias for crossover formation and promotes S-phase progression. Oppositely, the unique role of Rad61/Wapl is to promote non-crossover recombination by releasing [Pds5+Rec8]. For this effect, Rad61/Wapl probably acts to maintain homolog bias by preventing channeling into sister interactions. Mysteriously, each analyzed molecule has one role that involves neither of the other two. Overall, the presented findings suggest that Pds5's role in maintenance of sister chromatid cohesion during the mitotic prophase-analogous stage of G2/M is repurposed during meiosis prophase to promote interactions between homologs.
Topics: Cell Cycle Proteins; Cells, Cultured; Chromosomal Proteins, Non-Histone; Chromosome Pairing; Chromosome Segregation; Chromosomes, Fungal; Meiosis; Organisms, Genetically Modified; Protein Binding; Recombination, Genetic; S Phase; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins; Sister Chromatid Exchange
PubMed: 31617566
DOI: 10.1093/nar/gkz903