DMC1 FUNCTIONS IN A SACCHAROMYCES-CEREVISIAE MEIOTIC PATHWAY THAT IS LARGELY INDEPENDENT OF THE RAD51 PATHWAY

Meiotic recombination in the yeast Saccharomyces cerevisiae requires t wo similar recA-like proteins, Dmc1p and Rad51p. A screen for dominant meiotic mutants provided DMC1-G126D, a dominant allele mutated in the conserved ATP-binding site (specifically, the A-loop motif) that conf ers a null phenotype. A recessive null allele, dmc1-K69E, was isolated as an intragenic suppressor of DMC1-G126D. Dmc1-K69Ep, unlike Dmc1p, does not interact homotypically in a two-hybrid assay, although it doe s interact with other fusion proteins identified by two-hybrid screen with Dmc1p. Dmc1p, unlike Rad51p, does not interact in the two-hybrid assay with Rad52p or Rad54p. However, Dmc1p does interact with Tid1p, a Rad54p homologue, with Tid4p, a Rad16p homologue, and with other fus ion proteins that do not interact with Rad51p, suggesting that Dmc1p a nd Rad51p function in separate, though possibly overlapping, recombina tional repair complexes. Epistasis analysis suggests that DMC1 and RAD 51 function in separate pathways responsible for meiotic recombination . Taken together, our results are consistent with a requirement for DM C1 for meiosis-specific entry of DNA double-strand break ends into chr omatin. Interestingly, the pattern on CHEF gels of chromosome fragment s that result from meiotic DNA double-strand break formation is differ ent in DMC1 mutant strains from that seen in rad50S strains.