Role of yeast SIR genes and mating type in directing DNA double-strand breaks to homologous and non-homologous repair paths.
Eukaryotes have acquired many mechanisms to repair DNA double-strand breaks (DSBs) [1]. In the yeast Saccharomyces cerevisiae, this damage can be repaired either by homologous recombination, which depends on the Rad52 protein, or by non-homologous end-joining (NHEJ), which depends on the proteins yKu70 and yKu80 [2] [3]. How do cells choose which repair pathway to use? Deletions of the SIR2, SIR3 and SIR4 genes - which are involved in transcriptional silencing at telomeres and HM mating-type loci (HMLalpha and HMRa) in yeast [4] - have been reported to reduce NHEJ as severely as deletions of genes encoding Ku proteins [5]. Here, we report that the effect of deleting SIR genes is largely attributable to derepression of silent mating-type genes, although Sir proteins do play a minor role in end-joining. When DSBs were made on chromosomes in haploid cells that retain their mating type, sir Delta mutants reduced the frequency of NHEJ by twofold or threefold, although plasmid end-joining was not affected. In diploid cells, sir mutants showed a twofold reduction in the frequency of NHEJ in two assays. Mating type also regulated the efficiency of DSB-induced homologous recombination. In MATa/MATalpha diploid cells, a DSB induced by HO endonuclease was repaired 98% of the time by gene conversion with the homologous chromosome, whereas in diploid cells with an alpha mating type (matDelta/MATalpha) repair succeeded only 82% of the time. Mating-type regulation of genes specific to haploid or diploid cells plays a key role in determining which pathways are used to repair DSBs.
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Rosenstiel Center, Department of Biology, Brandeis University, Waltham, Massachusetts 02454-9110, USA.
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Sylvan
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Haber
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D004249:DNA Damage; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D005656:Fungal Proteins / Q000235:genetics / Q000502:physiology*; D005800:Genes, Fungal / Q000502:physiology*; D049770:Genes, Mating Type, Fungal; D006655:Histone Deacetylases; D008957:Models, Genetic; D016296:Mutagenesis; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D056565:Sirtuin 2; D037761:Sirtuins; D013997:Time Factors; D015534:Trans-Activators / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic
D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C084122:SIR3 protein, S cerevisiae; C061573:SIR4 protein, S cerevisiae; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D015534:Trans-Activators; C087778:SIR2 protein, S cerevisiae; D056565:Sirtuin 2; D037761:Sirtuins; D006655:Histone Deacetylases