Published 5 December 2005. doi:10.1083/jcb.200506029
The Rockefeller University Press, 0021-9525 $8.00
JCB, Volume 171, Number 5, 765-771
Repair of double-strand breaks by nonhomologous end joining in the absence of Mre11
Michela Di Virgilio and
Jean Gautier
Department of Genetics and Development, Columbia University, New York, NY 10032
Correspondence to Jean Gautier: jg130{at}columbia.edu
Abstract
Mre11Rad50Nbs1 (MRN) complex involvement in nonhomologous end joining (NHEJ) is controversial. The MRN complex is required for NHEJ in Saccharomyces cerevisiae but not in Schizosaccharomyces pombe. In vertebrates, Mre11, Rad50, and Nbs1 are essential genes, and studies have been limited to cells carrying hypomorphic mutations in Mre11 or Nbs1, which still perform several MRN complexassociated activities. In this study, we analyze the effects of Mre11 loss on the mechanism of vertebrate NHEJ by using a chromatinized plasmid double-strand break (DSB) repair assay in cell-free extracts from Xenopus laevis. Mre11-depleted extracts are able to support efficient NHEJ repair of DSBs regardless of the end structure. Mre11 depletion does not alter the kinetics of end joining or the type and frequency of junctions found in repaired products. Finally, Ku70-independent end-joining events are not affected by Mre11 loss. Our data demonstrate that the MRN complex is not required for efficient and accurate NHEJ-mediated repair of DSBs in this vertebrate system.
Abbreviations used in this paper: ATLD, Ataxia telangiectasialike disorder; CC, closed circle; DNA-PKcs, DNA-dependent protein kinase catalytic subunit; DSB, double-strand break; LD, linear dimer; MRN, Mre11Rad50Nbs1; NHEJ, nonhomologous end joining; PSS, protruding single strand.

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