GENETIC-EFFECTS OF PHOTOACTIVATED PSORALENS DURING MEIOSIS IN DNA-REPAIR MUTANT PSO3-1 OF SACCHAROMYCES-CEREVISIAE

The influence of the DNA repair gene PSO3 on photoactivated psoralen-i nduced meiotic recombination, gene conversion, reverse mutation, and o n survival, was assayed in diploid strains of Saccharomyces cerevisiae homozygous for the wild-type or the pso3-1 mutant allele. Sporulation was normal in the pso3-1 diploid. Wild-type and mutant strains had th e same sensitivity to photoactivated monofunctional psoralen (3-CPs UVA) in meiosis-uncommitted and meiosis-committed stages. The mutant s howed higher sensitivity to photoactivated bifunctional psoralen (8-MO P + UVA) during all stages of the meiotic cycle. Mutation induction by 3CPs + UVA or 8-MOP + UVA in meiosis-committed cells revealed no sign ificant differences between wild-type and the pso3-1 mutant. The statu s of the PSO3 gene has no influence on the kinetics of induction of ge ne conversion and crossing-over after 3-CPs + UVA treatment in meiosis -committed cells: gene conversion was blocked while recombination was induced. After treatment with 8-MOP + UVA gene conversion was also blo cked in both strains while crossing-over could only be observed in mei osis-committed wild-type cells.