Homologous recombinational repair of double-strand breaks in yeast is enhanced by MAT heterozygosity through yKU-dependent and -independent mechanisms

Genetics. 2001 Feb;157(2):579-89. doi: 10.1093/genetics/157.2.579.


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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Alleles
  • Antigens, Nuclear*
  • Cell Division
  • DNA Damage / genetics*
  • DNA Helicases*
  • DNA Repair
  • DNA-Binding Proteins / genetics*
  • Diploidy
  • Haploidy
  • Heterozygote*
  • Ku Autoantigen
  • Mating Factor
  • Models, Genetic
  • Mutation
  • Nuclear Proteins / genetics*
  • Peptides / genetics*
  • Plasmids / metabolism
  • Protein Binding
  • Recombination, Genetic / genetics*
  • Saccharomyces cerevisiae Proteins*


  • Antigens, Nuclear
  • DNA-Binding Proteins
  • Nuclear Proteins
  • Peptides
  • Saccharomyces cerevisiae Proteins
  • YKU70 protein, S cerevisiae
  • high affinity DNA-binding factor, S cerevisiae
  • Mating Factor
  • DNA Helicases
  • XRCC5 protein, human
  • Xrcc6 protein, human
  • Ku Autoantigen