INTERACTION BETWEEN USTILAGO-MAYDIS REC2 AND RAD51 GENES IN DNA-REPAIR AND MITOTIC RECOMBINATION

A gene encoding a Ustilago maydis Rad51 orthologue has been isolated. rad51-1, a mutant constructed by disrupting the gene, was as sensitive to killing by ultraviolet light and gamma radiation as the rec2-1 mut ant and slightly more sensitive to killing by methyl methanesulfonate. There was no suppression of killing by ultraviolet light when a rec2- 1 strain was transformed with a multicopy plasmid containing RAD51, no r was there suppression when rad51-1 was transformed with a multicopy plasmid containing REC2. Recombination proficiency as measured by a ga p repair assay was diminished in both rec2-1 and rad51-1 strains. In r ec2-1 the frequency of recombination was decreased, but the spectrum o f events was similar to that observed in wild type, while in rad51-1 t he frequency as well as the spectrum of recombination events were diff erent. Studies with the rec2-1 rad51-1 double mutant indicated that th ere was epistasis in the action of REC2 and RAD51 in certain repair an d recombination functions, but some measure of independent action in o ther functions.