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 the DNA metabolic enzymes at various times in meiosis in wild type and repair-deficient cells of yeast. DNA polymerases I and II increase by approximately two and three times, respectively, during meiosis shortly before the time of meiotic DNA synthesis and recombination. Low levels of pH 8.0 single-strand deoxyribonuclease activity are observed in cells prior to the beginning of meiosis. The activity increases during meiosis beginning around the time of premeiotic DNA synthesis. Of particular interest is a nuclease under the control of the RAD52 gene. It increases five to ten-fold in RAD+ cells and decreases toward the end of meiosis. No activity is detected in rad52 cells. It therefore appears that there is a coordinated increase in enzyme systems involved in meiotic DNA synthesis and recombination. We are also investigating signals which might be involved in meiotic DNA metabolic events. Although there is very little methylation of DNA in yeast, it appears that there are sequences which become methylated or lose methylation during meiosis. The timing and function of these are being pursued. Antibodies which had been raised against several proteins associated with replication or DNA metabolism will be used to probe DNA metabolic activities during meiosis. Using various mutants and conditions of high meiotic efficiency, it may be possible to determine the roles of these proteins during meiotic replication and recombination.
