FURTHER CHARACTERIZATION OF THE YEAST PSO4-1 MUTANT - INTERACTION WITH RAD51 AND RAD52 MUTANTS AFTER PHOTOINDUCED PSORALEN LESIONS

The pso4-1 mutant was characterized as deficient in some types of reco mbination, including gene conversion, crossing over, and intrachromoso mal recombination, The mode of interaction between pso4-1 and rad51 an d between pso4-1 and rad52 mutants indicated that the PSO4 gene belong s to the RAD52 epistasis group for strand-break repair. Moreover, the presence of the pso4-1 mutation decreased 8-MOP-photoinduced mutagenes is of the rad51 and rad52 mutants. Complementation tests using heteroz ygous diploid strains showed that the Pso4 protein might interact with the Rad52 protein during repair of 8-MOP photolesions. The pso4-1 mut ant, even though defective in inter- and intra-chromosomal recombinati on, conserves the ability for plasmid integration of circular and line ar plasmid DNA, On the other hand, similar to the rad51 mutant, pso4-1 was able to incise but did not restore high-molecular-weight DNA duri ng the repair of cross links induced by 8-MOP plus UVA. These results, together with those of previous reports, indicate that the PSO4 gene belongs to the RAD52 DNA repair group and its product participates in the DNA rejoining step of the repair of cross-link lesions, which are crucial for induced mutagenesis and recombinogenesis.