title: Homologous recombinational repair of double-strand breaks in yeast is enhanced by MAT heterozygosity through yKU-dependent and -independent mechanisms.
abstract: DNA double-strand breaks (DSBs) are repaired by homologous recombination (HR) and nonhomologous end-joining (NHEJ). NHEJ in yeast chromosomes has been observed only when HR is blocked, as in rad52 mutants or in the absence of a homologous repair template. We detected yKu70p-dependent imprecise NHEJ at a frequency of approximately 0.1% in HR-competent Rad+ haploid cells. Interestingly, yku70 mutation increased DSB-induced HR between direct repeats by 1.3-fold in a haploid strain and by 1.5-fold in a MAT homozygous (a/a) diploid, but yku70 had no effect on HR in a MAT heterozygous (a/alpha) diploid. yku70 might increase HR because it eliminates the competing precise NHEJ (religation) pathway and/or because yKu70p interferes directly or indirectly with HR. Despite the yku70-dependent increase in a/a cells, HR remained 2-fold lower than in a/alpha cells. Cell survival was also lower in a/a cells and correlated with the reduction in HR. These results indicate that MAT heterozygosity enhances DSB-induced HR by yKu-dependent and -independent mechanisms, with the latter mechanism promoting cell survival. Surprisingly, yku70 strains survived a DSB slightly better than wild type. We propose that this reflects enhanced HR, not by elimination of precise NHEJ since this pathway produces viable products, but by elimination of yKu-dependent interference of HR.
authors.affiliation: Department of Molecular Genetics and Microbiology, University of New Mexico School of Medicine, Albuquerque, NM 87131, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Clikeman
authors.forename: G J
authors.initials: GJ
authors.lastname: Khalsa
authors.forename: S L
authors.initials: SL
authors.lastname: Barton
authors.forename: J A
authors.initials: JA
authors.lastname: Nickoloff
mesh_terms: D000483:Alleles; D034961:Antigens, Nuclear; D002455:Cell Division; D004249:DNA Damage / Q000235:genetics*; D004265:DNA Helicases; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000235:genetics*; D004171:Diploidy; D006238:Haploidy; D006579:Heterozygote; D000072200:Ku Autoantigen; D000072235:Mating Factor; D008957:Models, Genetic; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics*; D010455:Peptides / Q000235:genetics*; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D011995:Recombination, Genetic / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins
chemical_list: D034961:Antigens, Nuclear; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D010455:Peptides; D029701:Saccharomyces cerevisiae Proteins; C520769:YKU70 protein, S cerevisiae; C081647:high affinity DNA-binding factor, S cerevisiae; D000072235:Mating Factor; D004265:DNA Helicases; C106893:XRCC5 protein, human; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen