[Effect of hms mutations increasing spontaneous mutability on induced mutagenesis and mitotic recombination in the yeast Saccharomyces cerevisiae].

The influence of five nonallelic mutations hsm-1-hsm-5 on the frequency of mutations induced by UV-light, 6-hydroxyl-aminopurine (GAP) and nitrosomethylurea (NMM) at the ADE1 and ADE2 loci was studied. All hsm mutants were resistant to the lethal effect of these mutagens. The frequency of mutations induced by UV-light was increased in hsm2-1, hsm3-1, hsm5-1 and especially in hsm1-1 mutants, the hsm4-1 mutant not differing from the HSM strain. GAP-induced mutagenesis was elevated in all hsm mutants and, particularly, in hsm3-1. No influence of hsm mutations on the frequency of NMM-induced mutations was observed. The frequency of spontaneous mitotic gene conversion was studied in the diploids heteroallelic for mutations in the gene ADE2 (ade2-58 ade2-i) and homo- and heterozygous for the hsm mutations (HSMHSM and HSMhsm). The mutations hsm2-1, hsm3-1 and especially hsm5-1 strongly increased the conversion frequency for all heteroallelic combinations studied. The mutations hsm1-1, hsm4-1 affected this process weakly. The properties of the hsm mutations under study demonstrated common genetic control of spontaneous and induced mutagenesis and recombination in the yeast. Possible belonging of hsm mutations to the class of mutations destroying the repair pathway for mismatch correction is under discussion.