Abstract
DNA double-strand breaks (DSBs) are the most lethal form of DNA damage that can lead to the development of cancer and other diseases. In Saccharomyces cerevisiae, several homologous recombination (HR) mechanisms have evolved to repair such lesions. When one end of the DSB shares homology with another locus in the genome, repair occurs by break-induced replication (BIR), which leads to a nonreciprocal translocation of chromosome ends. Previous work in DNA damage has focused on the characterization of how cells sense and repair DSBs and my work contributes to this foundation. In this work, I studied site-specific DSBs induced by HO endonuclease to determine the mismatch tolerance and repair efficiency of Rad51-dependent mitotic recombination and Dmc1-dependent meiotic recombination. We find that Rad51 and Dmc1 show similar tolerances for mismatches but the monitoring of mismatches by the Msh2-dependent mismatch repair system is significantly different between mitotic and meiotic cells. I also investigated the repair by gene conversion (GC) when both ends of a break share homology with another locus in the genome. We show the effect of mismatched templates during GC and an inherent asymmetry of repair on the two sides of a DSB. Collectively, these results enhance the understanding of the regulation of the DNA repair pathways and highlight the mechanistic insight on the maintenance of genome integrity.