Repair of MMS-induced DNA double-strand breaks in haploid cells of Saccharomyces cerevisiae, which requires the presence of a duplicate genome

Mol Gen Genet. 1979 Jan 2;167(3):279-86. doi: 10.1007/BF00267420.


The formation and repair of double-strand breaks induced in DNA by MMS was studied in haploid wild type and MMS-sensitive rad6 mutant strains of Saccharomyces cerevisiae with the use of the neutral and alkaline sucrose sedimentation technique. A similar decrease in average molecular weight of double-stranded DNA from 5--6 X 10(8) to 1--0.7 X 10(8) daltons was observed following treatment with 0.5% MMS in wild type and mutant strains. Incubation of cells after MMS treatment in a fresh drug-free growing medium resulted in repair of double-strand breaks in the wild type stain, but only in the exponential phase of growth. No repair of double-strand breaks was found when cells of the wild type strain were synchronized in G-1 phase by treatment with alpha factor, although DNA single-strand breaks were still efficiently repaired. Mutant rad6 which has a very low ability to repair MMS-induced single-strand breaks, did not repair double-strand breaks regardless of the phase of growth. These results suggest that (1) repair of double-strand breaks requires the ability for single-strand breaks repair, (2) rejoining of double-strand breaks requires the availability of two homologous DNA molecules, this strongly supports the recombinational model of DNA repair.

MeSH terms

  • DNA Repair*
  • Haploidy
  • Methyl Methanesulfonate / pharmacology
  • Mutagens
  • Mutation
  • Phenotype
  • Recombination, Genetic*
  • Saccharomyces cerevisiae / genetics*


  • Mutagens
  • Methyl Methanesulfonate