Unique DNA metabolic activities have been implicated during meiosis and following exposure of mitotic cells to DNA damaging agents. We have characterized both the DNA and DNA metabolic enzymes at various times in meiosis in wild type and repair-deficient cells of yeast. No changes in the single-strand or double-strand size of chromosomal DNA are detected at any time during meiosis, while changes are observed in various mutants. Recombination is an important process in repair and in recombination. We are investigating proteins that might be involved in both processes. Previously we had shown that a RAD52 controlled nuclease increases nearly 10-fold, implicating it in meiotic recombination. We have purified a protein from cells that are undergoing meiosis that is able to carry out a strand exchange reaction. This reaction which involves the displacement of one of two strands from a duplex by another homologous singlestrand DNA molecule is generally considered to be one of the basic steps in recombination that take place within cells. The protein has a MW = 38,000 and does not have ATPase activity for is ATP required for the reaction. The appearance of the protein requires the RAD50 gene product and is meiosis specific. Strains that are homozygous for mating type (and therefore do not undergo meiosis do not accumulate this protein during meiosis. The role of the RAD52 gene is currently being examined since it appears to have control function. This is being done by domain mapping, i.e., using different rad52 mutants. The importance of chromosome pairing is also being examined using strains which undergo meiosis as haploids.
