The Mre11-Rad50-Xrs2 protein complex facilitates homologous recombination-based double-strand break repair in Saccharomyces cerevisiae

Saccharomyces cerevisiae mre11 Delta mutants are profoundly deficient in do uble-strand break (DSB) repair, indicating that the Mre11-Rad50-Xrs2 protei n complex plays a central role in the cellular response to DNA DSBs, In thi s study, we examined the role of the complex in homologous recombination, t he primary mode of DSB repair in yeast, We measured survival in synchronous cultures following irradiation and scored sister chromatid and interhomolo gue recombination genetically, mre11 Delta strains were profoundly sensitiv e to ionizing radiation (IR) throughout the cell cycle. Mutant strains exhi bited decreased frequencies of IR-induced sister chromatid and interhomolog ue recombination, indicating a general deficiency in homologous recombinati on-based DSB repair. Since a nuclease-deficient mre11 mutant was not impair ed in these assays, it appears that the role of the S. cerevisiae Mre11-Rad 50-Xrs2 protein complex in facilitating homologous recombination is indepen dent of its nuclease activities.