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Vol. 20, Issue 7, 2096-2107, April 1, 2009

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The Role of MRN in the S-Phase DNA Damage Checkpoint Is Independent of Its Ctp1-dependent Roles in Double-Strand Break Repair and Checkpoint Signaling

Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605

Submitted October 1, 2008; Revised January 28, 2009; Accepted January 30, 2009
Monitoring Editor: Daniel J. Lew

The Mre11-Rad50-Nbs1 (MRN) complex has many biological functions: processing of double-strand breaks in meiosis, homologous recombination, telomere maintenance, S-phase checkpoint, and genome stability during replication. In the S-phase DNA damage checkpoint, MRN acts both in activation of checkpoint signaling and downstream of the checkpoint kinases to slow DNA replication. Mechanistically, MRN, along with its cofactor Ctp1, is involved in 5' resection to create single-stranded DNA that is required for both signaling and homologous recombination. However, it is unclear whether resection is essential for all of the cellular functions of MRN. To dissect the various roles of MRN, we performed a structure–function analysis of nuclease dead alleles and potential separation-of-function alleles analogous to those found in the human disease ataxia telangiectasia-like disorder, which is caused by mutations in Mre11. We find that several alleles of rad32 (the fission yeast homologue of mre11), along with ctp1, are defective in double-strand break repair and most other functions of the complex, but they maintain an intact S phase DNA damage checkpoint. Thus, the MRN S-phase checkpoint role is separate from its Ctp1- and resection-dependent role in double-strand break repair. This observation leads us to conclude that other functions of MRN, possibly its role in replication fork metabolism, are required for S-phase DNA damage checkpoint function.

Address correspondence to: Nicholas Rhind (nick.rhind{at}umassmed.edu)

This article has been cited by other articles:

				N. Willis and N. Rhind The Fission Yeast Rad32(Mre11)-Rad50-Nbs1 Complex Acts Both Upstream and Downstream of Checkpoint Signaling in the S-Phase DNA Damage Checkpoint Genetics, April 1, 2010; 184(4): 887 - 897. [Abstract] [Full Text] [PDF]

				N. Milman, E. Higuchi, and G. R. Smith Meiotic DNA Double-Strand Break Repair Requires Two Nucleases, MRN and Ctp1, To Produce a Single Size Class of Rec12 (Spo11)-Oligonucleotide Complexes Mol. Cell. Biol., November 15, 2009; 29(22): 5998 - 6005. [Abstract] [Full Text] [PDF]