The Mre11-Rad50-Xrs2 Protein Complex Facilitates Homologous Recombination-Based Double-Strand Break Repair in Saccharomyces cerevisiae

Abstract

Saccharomyces cerevisiae mre11Δ mutants are profoundly deficient in double-strand break (DSB) repair, indicating that the Mre11-Rad50-Xrs2 protein complex plays a central role in the cellular response to DNA DSBs. In this study, we examined the role of the complex in homologous recombination, the primary mode of DSB repair in yeast. We measured survival in synchronous cultures following irradiation and scored sister chromatid and interhomologue recombination genetically. mre11Δ strains were profoundly sensitive to ionizing radiation (IR) throughout the cell cycle. Mutant strains exhibited decreased frequencies of IR-induced sister chromatid and interhomologue recombination, indicating a general deficiency in homologous recombination-based DSB repair. Since a nuclease-deficient mre11 mutant was not impaired in these assays, it appears that the role of the S. cerevisiae Mre11-Rad50-Xrs2 protein complex in facilitating homologous recombination is independent of its nuclease activities.

ACKNOWLEDGMENTS

We are grateful to the members of our lab for insights throughout the course of this study, Michael Fasullo and Jim Haber for providing reagents, Barbara Garvik for advice and for providing yeast strains, and Mark Kaplan, Doug Bishop, and Michael Lichten for critical reading of the manuscript.

This work was supported by the Milwaukee Foundation, the Howard Hughes Medical Institute, the National Cancer Institute, NIH grant GM56888 (to J.H.J.P.), NIH predoctoral training grant 5T32GM07133 (to D.A.B.), and cancer biology postdoctoral training grant NCI T32-CA09471 to the University of Wisconsin Comprehensive Cancer Center (B.K.B.).