Induction and repair of gene conversion in UV-sensitive mutants of yeast

Summary Photoreactivation effect on UV-induced allelic recombination has been examined using various combinations of leu1 alleles in UV-sensitive and wild type diploid yeast, Saccharomyces cerevisiae. The frequencies of UV-induced heteroallelic reversion in UV-sensitive strains, presumably lacking dark-repair, are strikingly enhanced compared to those in wild type at the same doses under dark condition. However, these enhanced frequencies of reversion are diminished by photoreactivation almost to the level of those in wild type. The induced frequencies of homoallelic reversion (mutation) of relevant alleles are apparently lower than those of heteroallelic reversion. Phenotypic analysis for linked gene leu1 on UV-induced heteroallelic revertants has shown that most of the revertants are of the nonreciprocal type recombination (mitotic gene conversion). These results would indicate that most of the dark-repairable damage leading to mitotic gene conversion after UV-light is due to pyrimidine dimers.On leave of absence from Radiation Center of Osaka Prefecture, Shinke-cho Sakai, Osaka, Japan.