Cell Reports - Molecular Basis for DNA Double-Strand Break Annealing and Primer Extension by an NHEJ DNA Polymerase

Cell Reports - Molecular Basis for DNA Double-Strand Break Annealing and Primer Extension by an NHEJ DNA Polymerase

Molecular Basis for DNA Double-Strand Break Annealing and Primer Extension by an NHEJ DNA Polymerase

Cell Reports, Volume 5, Issue 4, 1108-1120, 14 November 2013
Copyright © 2013 The Authors
10.1016/j.celrep.2013.10.016
This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Authors

Nigel C. Brissett,Maria J. Martin,Edward J. Bartlett,Julie Bianchi,Luis Blanco,Aidan J. DohertySee Affiliations

• Highlights
• Structure of a NHEJ polymerase bound to an annealed DNA double-strand break
• Break synapsis is stabilized by microhomology and polymerase surface loops
• 3′ hydroxyl of the primer strand is positioned into active-site pocket in trans
• Templating base selection relies on loop 1 and conserved phenylalanine residues

Summary

Nonhomologous end-joining (NHEJ) is one of the major DNA double-strand break (DSB) repair pathways. The mechanisms by which breaks are competently brought together and extended during NHEJ is poorly understood. As polymerases extend DNA in a 5′-3′ direction by nucleotide addition to a primer, it is unclear how NHEJ polymerases fill in break termini containing 3′ overhangs that lack a primer strand. Here, we describe, at the molecular level, how prokaryotic NHEJ polymerases configure a primer-template substrate by annealing the 3′ overhanging strands from opposing breaks, forming a gapped intermediate that can be extended in trans. We identify structural elements that facilitate docking of the 3′ ends in the active sites of adjacent polymerases and reveal how the termini act as primers for extension of the annealed break, thus explaining how such DSBs are extended in trans. This study clarifies how polymerases couple break-synapsis to catalysis, providing a molecular mechanism to explain how primer extension is achieved on DNA breaks.