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EMBO J. 2012 Dec 12;31(24):4576-86. doi: 10.1038/emboj.2012.313. Epub 2012 Nov 27.

The fission yeast MRN complex tethers dysfunctional telomeres for NHEJ repair.

Author information

1
Instituto Gulbenkian de Ciência, Oeiras, Portugal.

Abstract

Telomeres protect the natural ends of chromosomes from being repaired as deleterious DNA breaks. In fission yeast, absence of Taz1 (homologue of human TRF1 and TRF2) renders telomeres vulnerable to DNA repair. During the G1 phase, when non-homologous end joining (NHEJ) is upregulated, taz1Δ cells undergo telomere fusions with consequent loss of viability. Here, we show that disruption of the fission yeast MRN (Rad23(MRE11)-Rad50-Nbs1) complex prevents NHEJ at telomeres and, as a result, rescues taz1Δ lethality in G1. Neither Tel1(ATM) activation nor 5'-end resection was required for telomere fusion. Nuclease activity of Rad32(MRE11) was also dispensable for NHEJ. Mutants unable to coordinate metal ions required for nuclease activity were proficient in NHEJ repair. In contrast, Rad32(MRE11) mutations that affect binding and/or positioning of DNA ends leaving the nuclease function largely unaffected also impaired NHEJ at telomeres and restored the viability of taz1Δ in G1. Consistently, MRN structural integrity but not nuclease function is also required for NHEJ of independent DNA ends in a novel split-molecule plasmid assay. Thus, MRN acts to tether unlinked DNA ends, allowing for efficient NHEJ.

PMID:
23188080
PMCID:
PMC3545291
DOI:
10.1038/emboj.2012.313
[Indexed for MEDLINE]
Free PMC Article

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