[HSM6 gene is identical to PSY4 gene in Saccharomyces cerevisiae yeasts]

Previously, we isolated mutant yeasts Saccharomyces cerevisiae with an increased rate of spontaneous mutagenesis. Here, we studied the properties of HSM6 gene, the hsm6-1 mutation of which increased the frequency of UV-induced mutagenesis and decreased the level of UV-induced mitotic crossover at the centromere gene region, ADE2. HSM6 gene was mapped on the left arm of chromosome 11 in the region where the PSY4 gene is located. The epistatic analysis has shown that the hsm6-1 mutation represents an allele of PSY4 gene. Sequencing of hsm6-1 mutant allele has revealed a frameshift mutation, which caused the substitution of Lys218Glu and the generation of a stop codon in the next position. The interactions of hsm6-1 and rad52 mutations were epistatic. Our data show that the PSY4 gene plays a key role in the regulation of cell withdrawal from checkpoint induced by DNA disturbances.