Pch2 Modulates Chromatid Partner Choice During Meiotic Double-Strand Break Repair in Saccharomyces cerevisiae

In most organisms, the segregation of chromosomes during the first meiotic division is dependent upon at least one crossover (CO) between each pair of homologous chromosomes. COs can result from chromosome double-strand breaks (DSBs) that are induced and preferentially repaired using the homologous chromosome as a template. The PCH2 gene of budding yeast is required to establish proper meiotic chromosome axis structure and to regulate meiotic interhomolog DSB repair outcomes. These roles appear conserved in the mouse ortholog of PCH2, Trip13, which is also involved in meiotic chromosome axis organization and the regulation of DSB repair. Using a combination of genetic and physical assays to monitor meiotic DSB repair, we present data consistent with pch2 Delta mutants showing defects in suppressing intersister DSB repair. These defects appear most pronounced in dmc1 Delta mutants, which are defective for interhomolog repair, and explain the previously reported observation that pch2 Delta dmc1 Delta cells can complete meiosis. Results from genetic epistasis analyses involving spo13 Delta, rad54 Delta, and mek1/MEK1 alleles and an intersister recombination reporter assay are also consistent with Pch2 acting to limit intersister repair. We propose a model in which Pch2 is required to promote full Mek1 activity and thereby promotes interhomolog repair.