Mutants defective in Rad1-Rad10-Slx4 exhibit a unique pattern of viability during mating type switching in Saccharomyces cerevisiae

Efficient repair of DNA double-strand breaks (DSBs) requires the coordination of checkpoint signaling and enzymatic repair functions. To study these processes during gene conversion at a single chromosomal break, we monitored mating type switching in S. cerevisiae strains defective in the Rad1-Rad10-Slx4 complex. Rad1-Rad10 is a structure-specific endonuclease that removes 3' nonhomologous single-stranded ends that are generated during many recombination events. Slx4 is a known target of the DNA damage response that forms a complex with Rad1-Rad10 and is critical for 3' end processing during repair of DSBs by single-strand annealing. We found that mutants lacking an intact Rad1-Rad10-Slx4 complex displayed RAD9- and MAD2-dependent cell cycle delays and decreased viability during mating type switching. In particular, these mutants exhibited a unique pattern of dead and switched daughter cells arising from the same DSB-containing cell. Furthermore, we observed that mutations in post-replicative lesion bypass factors (mms2, mph1) resulted in decreased viability during mating type switching, and conferred shorter cell cycle delays in rad1; mutants. We conclude that Rad1-Rad10-Slx4 promotes efficient repair during gene conversion events involving a single 3' nonhomologous tail, and propose that the rad1 and slx4 mutant phenotypes result from inefficient repair of a lesion at the MAT locus that is bypassed by replication-mediated repair.

Key Words: Msh2-Msh3, Rad1-Rad10, Slx4, mating type switching, nonhomologous tail

Online ISS 1091-6490
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