title: The fission yeast MRN complex tethers dysfunctional telomeres for NHEJ repair.
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.
authors.affiliation: Instituto Gulbenkian de Ciência, Oeiras, Portugal.
authors.forename: Clara Correia
authors.initials: CC
authors.lastname: Reis
authors.forename: Sílvia
authors.initials: S
authors.lastname: Batista
authors.forename: Miguel Godinho
authors.initials: MG
authors.lastname: Ferreira
mesh_terms: D002470:Cell Survival / Q000502:physiology; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism; D059766:DNA End-Joining Repair / Q000502:physiology*; D017931:DNA Primers / Q000235:genetics; D016521:Electrophoresis, Gel, Pulsed-Field; D005090:Exodeoxyribonucleases / Q000378:metabolism; D016193:G1 Phase / Q000502:physiology*; D046912:Multiprotein Complexes / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D012568:Schizosaccharomyces; D029702:Schizosaccharomyces pombe Proteins / Q000378:metabolism; D016615:Telomere / Q000378:metabolism*; D034501:Telomere-Binding Proteins / Q000172:deficiency
chemical_list: D002868:Chromosomal Proteins, Non-Histone; D017931:DNA Primers; D046912:Multiprotein Complexes; C478035:Nbs1 protein, S pombe; C480032:Rad50 protein, S pombe; D029702:Schizosaccharomyces pombe Proteins; D034501:Telomere-Binding Proteins; C104344:taz1 protein, S pombe; D005090:Exodeoxyribonucleases; C092453:Mre11 protein, S pombe