The involvement of cellular recombination and repair genes in RNA-mediated recombination in Saccharomyces cerevisiae.

We previously demonstrated that a reverse transcript of a cellular reporter gene (his3-AI) can serve as the donor for gene conversion of a chromosomal his3-deltaMscI target sequence, and that this process requires the yeast recombination gene RAD52. In this study, we examine the involvement of other recombination and repair genes in RNA-mediated recombination, and gain insight into the nature of the recombination intermediate. We find that mutation of the mitotic RecA homologs RAD51, RAD55, and RAD57 increases the rate of RNA-mediated recombination relative to the wild type, and that these gene functions are not required for RNA-mediated gene conversion. Interestingly, RAD1 is required for RNA-mediated gene conversion of chromosomal his3-deltaMscI sequences, suggesting that the cDNA intermediate has a region of nonhomology that must be removed during recombination with target sequences. The observation that both RAD1 and RAD52 are required for RNA-mediated gene conversion of chromosomal but not plasmid sequences indicates a clear difference between these two pathways of homologous RNA-mediated recombination.