Nonhomologous End-Joining with Minimal Sequence Loss Is Promoted by the Mre11-Rad50-Nbs1-Ctp1 Complex in Schizosaccharomyces pombe.

While the Mre11-Rad50-Nbs1 (MRN) complex has known roles in repair processes like homologous recombination and microhomology-mediated end-joining, its role in nonhomologous end-joining (NHEJ) is unclear as Saccharomyces cerevisiae, Schizosaccharomyces pombe, and mammals have different requirements for repairing cut DNA ends. Most double-strand breaks (DSBs) require nucleolytic processing prior to DNA ligation. Therefore, we studied repair using the Hermes transposon, whose excision leaves a DSB capped by hairpin ends similar to structures generated by palindromes and trinucleotide repeats. We generated single Hermes insertions using a novel S. pombe transient transfection system, and used Hermes excision to show a requirement for MRN in the NHEJ of nonligatable ends. NHEJ repair was indicated by the >1000-fold decrease in excision in cells lacking Ku or DNA ligase 4. Most repaired excision sites had <5 bp of sequence loss or mutation, characteristic for NHEJ and similar excision events in metazoans, and in contrast to the more extensive loss seen in S. cerevisiaeS. pombe NHEJ was reduced >1000-fold in cells lacking each MRN subunit, and loss of MRN-associated Ctp1 caused a 30-fold reduction. An Mre11 dimer is thought to hold DNA ends together for repair, and Mre11 dimerization domain mutations reduced repair 300-fold. In contrast, a mre11 mutant defective in endonucleolytic activity, the same mutant lacking Ctp1, or the triple mutant also lacking the putative hairpin nuclease Pso2 showed wild-type levels of repair. Thus, MRN may act to recruit the hairpin opening activity that allows subsequent repair.

Li Y ，Wang J ，Zhou G ，Lajeunesse M ，Le N ，Stawicki BN ，Corcino YL ，Berkner KL ，Runge KW ... -  《-》

Release of Ku and MRN from DNA ends by Mre11 nuclease activity and Ctp1 is required for homologous recombination repair of double-strand breaks.

Langerak P ，Mejia-Ramirez E ，Limbo O ，Russell P ... -  《PLoS Genetics》

A curious new role for MRN in Schizosaccharomyces pombe non-homologous end-joining.

Runge KW ，Li Y 《-》

The Mre11/Rad50/Xrs2 complex and non-homologous end-joining of incompatible ends in S. cerevisiae.

Zhang X ，Paull TT 《-》

Ctp1 is a cell-cycle-regulated protein that functions with Mre11 complex to control double-strand break repair by homologous recombination.

Limbo O ，Chahwan C ，Yamada Y ，de Bruin RA ，Wittenberg C ，Russell P ... -  《-》