The Nuclease Activity of Mre11 Is Required for Meiosis but Not for Mating Type Switching, End Joining, or Telomere Maintenance

Abstract

The Saccharomyces cerevisiae MRE11 gene is required for the repair of ionizing radiation-induced DNA damage and for the initiation of meiotic recombination. Sequence analysis has revealed homology between Mre11 and SbcD, the catalytic subunit of an Escherichia coli enzyme with endo- and exonuclease activity, SbcCD. In this study, the purified Mre11 protein was found to have single-stranded endonuclease activity. This activity was absent from mutant proteins containing single amino acid substitutions in either one of two sequence motifs that are shared by Mre11 and SbcD. Mutants with allele mre11-D56N or mre11-H125Nwere partially sensitive to ionizing radiation but lacked the other mitotic phenotypes of poor vegetative growth, hyperrecombination, defective nonhomologous end joining, and shortened telomeres that are characteristic of the mre11 null mutant. Diploids homozygous for the mre11-H125N mutation failed to sporulate and accumulated unresected double-strand breaks (DSB) during meiosis. We propose that in mitotic cells DSBs can be processed by other nucleases that are partially redundant with Mre11, but these activities are unable to process Spo11-bound DSBs in meiotic cells.

ACKNOWLEDGMENTS

We thank members of the Symington laboratory and W. Holloman for critical reading of the manuscript. We thank H. Tsubouchi and H. Ogawa for providing plasmid pKJ1101, H. Smith for construction of pBM272-HO, and H. Klein, A. Mitchell, A. Rattray, R. Rothstein, and D. Shore for providing yeast strains.

This work was supported by Public Health Service grants GM41784 and 2 T32 CA09503 from the National Institutes for Health and the National Cancer Institute, respectively.