Identification and characterization of genes required for RAD51-independent recombination

he genes in the RAD52 epistasis group of Saccharomyces cerevisiae are necessary for most meiotic and mitotic recombination events. With the use of an intrachromosomal inverted-repeat as a recombination reporter it has previously been shown that mitotic recombination is dependent on the RAD52 gene because a rad52 mutation reduces recombination more than 3000-fold. However, recombination is only reduced 4 to 5-fold by mutation of RAD51 which encodes a homologue of bacterial RecA proteins. This result indicates that a RAD51-independent recombination mechanism exists in mitotic cells. To identify components of the RAD51-independent pathway, a rad51 strain containing a recombination reporter was mutagenized and mutants showing reduced levels of recombination were isolated. One mutation identified, rad59, reduced recombination 1100-fold in the presence of a rad51 mutation, but only 4 to 5-fold in a wild-type background. Thus the rad51 and rad59 mutations reduce recombination synergistically. The rad59 mutant strain is sensitive to ;The second mutation identified in this screen was a missense mutation in RAD52, named rad52R70K. This mutation makes yeast cells partially sensitive to...