Mre11-Rad50-Nbs1 is a keystone complex connecting DNA repair machinery, double-strand break signaling, and the chromatin template

Biochem Cell Biol. 2007 Aug;85(4):509-20. doi: 10.1139/O07-069.


The Mre11-Rad50-Nbs1 (MRN) complex is providing paradigm-shifting results of exceptional biomedical interest. MRN is among the earliest respondents to DNA double-strand breaks (DSBs), and MRN mutations cause the human cancer predisposition diseases Nijmegen breakage syndrome and ataxia telangiectasia-like disorder (ATLD). MRN's 3-protein multidomain composition promotes its central architectural, structural, enzymatic, sensing, and signaling functions in DSB responses. To organize the MRN complex, the Mre11 exonuclease directly binds Nbs1, DNA, and Rad50. Rad50, a structural maintenance of chromosome (SMC) related protein, employs its ATP-binding cassette (ABC) ATPase, Zn hook, and coiled coils to bridge DSBs and facilitate DNA end processing by Mre11. Contributing to MRN regulatory roles, Nbs1 harbors N-terminal phosphopeptide interacting FHA and BRCT domains, as well as C-terminal ataxia telangiectasia mutated (ATM) kinase and Mre11 interaction domains. Current emerging structural and biological evidence suggests that MRN has 3 coupled critical roles in DSB sensing, stabilization, signaling, and effector scaffolding: (1) expeditious establishment of protein--nucleic acid tethering scaffolds for the recognition and stabilization of DSBs; (2) initiation of DSB sensing, cell-cycle checkpoint signaling cascades, and establishment of epigenetic marks via the ATM kinase; and (3) functional regulation of chromatin remodeling in the vicinity of a DSB.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Review

MeSH terms

  • Acid Anhydride Hydrolases
  • Ataxia Telangiectasia Mutated Proteins
  • Cell Cycle Proteins / metabolism*
  • Chromatin / genetics
  • Chromatin / metabolism*
  • DNA / chemistry
  • DNA / genetics
  • DNA / metabolism
  • DNA Breaks, Double-Stranded*
  • DNA Repair Enzymes / metabolism*
  • DNA Repair*
  • DNA-Binding Proteins / metabolism*
  • Enzyme Activation
  • Humans
  • MRE11 Homologue Protein
  • Macromolecular Substances
  • Models, Molecular
  • Nuclear Proteins / metabolism*
  • Protein Conformation
  • Protein Serine-Threonine Kinases / metabolism
  • Signal Transduction / physiology
  • Tumor Suppressor Proteins / metabolism


  • Cell Cycle Proteins
  • Chromatin
  • DNA-Binding Proteins
  • MRE11 protein, human
  • Macromolecular Substances
  • NBN protein, human
  • Nuclear Proteins
  • Tumor Suppressor Proteins
  • DNA
  • ATM protein, human
  • Ataxia Telangiectasia Mutated Proteins
  • Protein Serine-Threonine Kinases
  • MRE11 Homologue Protein
  • Acid Anhydride Hydrolases
  • RAD50 protein, human
  • DNA Repair Enzymes