Saccharomyces cerevisiae G2 checkpoint and double‐strand break (DSB) repair genes synergistically suppress the formation of homology‐directed translocations

Abstract

Checkpoint and DNA repair mutants exhibit more genetic instability compared to wild‐type yeast. We previously observed that G2 checkpoint and rad51 mutants exhibit elevated rates of spontaneous translocations. We measured rates of spontaneous translocations in diploid mutants defective in checkpoint and/or DSB repair genes. Directed translocation events were measured by selecting for His+ recombinants that result from mitotic recombination between two truncated his3 genes. The rate of spontaneous translocations in wild type is 4.4 x 10−8. Whereas rad51 and rad9 mutants exhibited fourfold and sevenfold higher rates of spontaneous translocations, rad51 rad9 double mutants exhibited 39‐fold higher rate. Compared to rad51 rad9, we observed similar rates in rad55 rad9 and rad57 rad9 mutants. While xrs2, rad50, and mre11 mutants exhibited 10‐20 fold higher rates, compared to wild type, xrs2 rad9, rad50 rad9, and mre11 rad9 exhibited similar rates compared to rad51 rad9. Interestingly, rate of spontaneous translocations in mec1‐21, a S phase checkpoint mutant that retains some G2 checkpoint function, was 23‐fold higher than wild type, while rates in mec1‐21 rad51 double mutants were 100‐fold higher. Pulse field gel electrophoresis confirmed that recombinants contain translocations. The results illustrate that both DSB repair pathways and G2 checkpoint pathways suppress translocation frequencies.Grant support: CA70105 from the National Cancer Institute