Isolation and characterization of new nuclear srm gene mutation causing coordinated changes in the maintenance of nuclear and mitochondrial genetic structures in the yeast Saccharomyces

From grown cultures of UV-irradiated Saccharomyces cerevisiae cells with disomy at chromosome IV, clones with nuclear gene mutations were isolated, each of which was suggested to change both mitochondrial spontaneous rho- mutability and the mitotic stability of extra natural chromosomes. Four such nonallelic mutations (srm8, srm12, srm15, and srm17) were isolated, and their phenotypic expression characterized. All four mutations are associated with decreased spontaneous rho- mutability and virtually block sporulation in homozygous mutant diploids. Mutation srm8 is temperature-sensitive and, most probably, involves an essential gene. Double mutants of genotypes srm8 cdc28-srm and srm8 srm12 are nonviable. Mutation srm12 increases the rate of spontaneous loss of extra chromosome XIV by disomics by a factor of about 30. Mutation srm15 induces a small (about twofold) but statistically significant decrease of this rate. Mutations srm8 and srm17 drastically decelerate reproduction of cells with disomy, which prevents quantitative estimations of rates of loss of extra chromosomes.