Background: Rad51 and Dmc1 are Saccharomyces cerevisiae homologues of the Escherichia coli recombination protein RecA. Mutant analysis has shown that both proteins are required for normal meiotic recombination, for timely and efficient formation of synaptonemal complex and for normal progression out from meiotic prophase.
Results: We have further characterized rad51 and dmc1 single mutants. A dmc1 mutation confers more severe defects in double strand break (DSB) resolution, crossover recombination and meiotic progression than does a rad51 mutant; in contrast, during return to growth, a rad51 mutation confers more severe defects in viability and intrachromosomal recombination than does a dmc1 mutation. Analysis of a rad51 dmc1 double mutant, in parallel with single mutants, shows that the double mutant is more defective with respect to the formation of crossovers during meiosis and, especially strikingly, with respect to interhomologue and intrachromosomal recombination during return to growth. Consistent with the observation of DMC1-dependent recombination in a rad51 mutant, subnuclear complexes of Dmc1 protein were detected for the first time in this mutant. In contrast to the effects on recombination, the effect of the double mutant on meiotic progression was similar to that of the rad51 single mutant.
Conclusion: Rad51 and Dmc1 each make unique contributions to meiotic recombination. However, the two proteins are capable of substituting for one another under some circumstances, implying that they most likely share at least one recombination function. Recombination and cell cycle phenotypes are all consistent with the possibility that a dmc1 mutation causes an arrest of the post-DSB recombination complexes at a later, more stable stage than does a rad51 mutation.