Decision-making during NHEJ: a network of interactions in human Polμ implicated in substrate recognition and end-bridging

Nucleic Acids Res. 2014 Jul;42(12):7923-34. doi: 10.1093/nar/gku475. Epub 2014 May 30.


Human Polμ is a DNA polymerase belonging to the X family that has been implicated in the non-homologous end-joining (NHEJ) pathway during repair of double-strand breaks in DNA. Loop1 is a flexible piece of Polμ which has a critical role during terminal transferase and end-joining activities: it acts as a pseudo-template when the template strand is discontinuous or unavailable, whilst diffusing away if present to avoid steric clashes. Mutational analysis and inspection of the 3D structures available allowed us to identify a network of residues in charge of sensing the presence or absence of discontinuities in the template strand, which will in turn determine the final position adopted by Loop1. This network is formed by the previously uncharacterized thumb mini-loop (NSH motif) and the positively charged helix N, which contribute to the correct positioning of Loop1 and to juxtapose the discontinuous template strand during NHEJ of incompatible ends. Accordingly, single mutation of specific conserved residues in these motifs, whilst irrelevant in most of the cases for gap filling, largely affected terminal transferase and end-joining activities. Other point mutations in the 'hinges' of Loop1, such as residues Phe385 or Phe389, corroborated the flexibility requirements of this motif.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arginine / chemistry
  • DNA End-Joining Repair*
  • DNA Nucleotidylexotransferase / chemistry
  • DNA Nucleotidylexotransferase / genetics
  • DNA Nucleotidylexotransferase / metabolism
  • DNA-Directed DNA Polymerase / chemistry*
  • DNA-Directed DNA Polymerase / genetics
  • DNA-Directed DNA Polymerase / metabolism
  • Humans
  • Models, Molecular
  • Mutation


  • Arginine
  • DNA polymerase mu
  • DNA Nucleotidylexotransferase
  • DNA-Directed DNA Polymerase