Multiple mutant analysis of recombination in yeast

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Abstract
The RAD6, RAD50, and RAD52 loci have been identified as genes which code for functions which may act during meiotic recombination in yeast (Game et al. 1980; Prakash et al. 1980). By use of the spo13-1 mutation, which allows sporulating cells to bypass the first meiotic division, the rad50-1 mutation has been directly implicated as a general meiotic Rec- mutation by examination of viable ascospores (Malone and Esposito 1981). Since the rad6-1 and rad52-1 mutations do not yield viable ascospores in the presence of spo13-1, multiple rad mutants have been constructed and analyzed. This analysis has demonstrated that in meiosis rad50-1 is epistatic to rad52-1, and rad6-1 is epistatic to rad50-1. This suggests that the order of action of these genes during meiosis is RAD6, RAD50, and then RAD52. The data for rad6-1 can be interpreted to suggest that RAD6 may not code for a recombination function, per se, although it may be required for recombination to occur. Analysis of mitotic recombination indicates that rad52-1 is epistatic to rad50-1; in mitosis; this is consistent with the hypothesis that the RAD50 gene codes for a recombination function required in meiosis but not in mitosis.