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

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.

Endonuclease for apurinic sites in yeast. Comparison of the enzyme activity in the wild type and in rad mutants of Saccharomyces cerevisiae to MNS.

It was found that yeast cells contain an endonuclease specific for apurinic sites in DNA which has no effect on DNA with normal strands or on strands with alkylated sites. The enzyme activity was studied in the RAD strain and in rad 6, rad 18-2 and rad 21 mutants, all very sensitive to MMS, as compared to the wild type. The level of endonuclease activity does not differ much between the tested strains, regardless of their differences in susceptibility to MMS.

Alkaline sucrose sedimentation studies of MMS-induced DNA single-strand breakage and rejoining in the wild type and in UV-sensitive mutants of Saccharomyces cerevisiae.

MMS-induced DNA single-strand breakage and rejoining was studied in the RAD strain and in rad6 and rad21 mutants, both very sensitive to this treatment as compared with the wild type. Alkaline sucrose gradient centrifugation showed that MMS treatment reduced the molecular weight of DNA in the RAD strain and in rad6 and rad21 mutants to the same extent. Four hours of post-incubation in synthetic growth medium after treatment with a dose of 0.

Macromolecular synthesis during conjugation in yeast.

Morphological changes and synthesis of DNA, RNA and protein during conjugation of Saccharomyces cerevisiae was studied. It was found that during conjugation distinct cell expansion and increase in the dry mass of the cell takes place. DNA synthesis is inhibited during mating while synthesis of RNA and protein is not affected.