MRE11 within the MRE11-RAD50-NBS1 (MRN) complex acts in DNA double-strand break repair (DSBR), detection, and signaling; yet, how its endo- and exonuclease activities regulate DSBR by nonhomologous end-joining (NHEJ) versus homologous recombination (HR) remains enigmatic. Here, we employed structure-based design with a focused chemical library to discover specific MRE11 endo- or exonuclease inhibitors. With these inhibitors, we examined repair pathway choice at DSBs generated in G2 following radiation exposure. While nuclease inhibition impairs radiation-induced replication protein A (RPA) chromatin binding, suggesting diminished resection, the inhibitors surprisingly direct different repair outcomes. Endonuclease inhibition promotes NHEJ in lieu of HR, while exonuclease inhibition confers a repair defect. Collectively, the results describe nuclease-specific MRE11 inhibitors, define distinct nuclease roles in DSB repair, and support a mechanism whereby MRE11 endonuclease initiates resection, thereby licensing HR followed by MRE11 exonuclease and EXO1/BLM bidirectional resection toward and away from the DNA end, which commits to HR. © 2014 Elsevier Inc. All rights reserved.
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Aab Shibata, Moiani, Dcd, Arvai, A. Scd, Perry, Jcd e, Harding, S. Mf, Genois, M. - Mg, Maity, Rg, van Rossum-Fikkert, Sh, Kertokalio, Ah, Romoli, Fi, Ismail, Aa, Ismalaj, Ei, Petricci, Ei, Neale, M. Ja, Bristow, R. Gf, Masson, J. - Yg, Wyman, Ch, Jeggo, P. Aa, and Tainer, J. Acd, “DNA Double-Strand Break Repair Pathway Choice Is Directed by Distinct MRE11 Nuclease Activities”, Molecular Cell, 2013.