We are investigating the unique chromosomal metabolic events associated with meiosis and the repair of chromosomes following exposure to DNA damaging agents. Many of the genes necessary for the repair of DNA double strand breaks (DSB) are required for the successful completion of the meiotic cycle. Previously, the DNA has been characterized from various stages of meiosis in both 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. From this, we have begun investigating the proteins/enzymes that might be involved in both repair and meiosis. We have purified two enzymes which may play a role in meiosis and/or repair; a Mg2+ dependant nuclease (yNucR) and a protein that is able to carry out a strand exchange reaction (SEP). Both of these proteins appear to be under the control of the RAD52 gene, a gene required for the repair of radiation induced DSB and the completion of meiosis. This suggests that the RAD52 gene has a control function. In order to investigate the role of RAD52, we have created strains which contain complete deletions of the RAD52 gene and contain a copy of RAD52 under the control of the yeast GAL1 promoter. Thus we are able to precisely regulate the cellular levels of the RAD52 protein (and therefore DSB repair) by the carbon source in the growth media. Using this unique construct we have found that for the repair of DSB the presence RAD52 protein is required prior to treatment with ionizing radiation. We will use this """"""""conditional"""""""" RAD52 to investigate the apparent control of yNucR and SEP.
