The effect of him mutations characterized by enhanced induced mutagenesis on the spontaneous mitotic recombination in the ADE2 gene in Saccharomyces cerevisiae

We have studied the influence of him1, him2, him3 and himX mutations on the frequency of spontaneous mitotic gene conversion in the yeast Saccharomyces cerevisiae using the set of heteroallelic combinations in the ADE2 gene. Data obtained on the HIM/HIM, him/him homozygotes and HIM/him heterozygotes indicate that the him1 mutation is recessive with respect to conversion, whereas the him2, him3 and himX mutations are semidominant. Gene conversion was increased in the majority of heteroalleles of mutant diploids him1/him1. On the contrary, the him2, him3 and himX mutants have hypo-rec phenotypes on mitotic conversion. The him mutations do not affect some heteroalleles, moreover, for some heteroalleles, the effects of the him mutations was opposite. On the basis of the sum of genetical data and, particularly, of conversion event pattern in the him mutants, we suggest that him mutations analysed affect the repair pathway for mismatch correction.