DNA synthesis by Pol η promotes fragile site stability by preventing under-replicated DNA in mitosis

J Cell Biol. 2013 Apr 29;201(3):395-408. doi: 10.1083/jcb.201207066. Epub 2013 Apr 22.


Human DNA polymerase η (Pol η) is best known for its role in responding to UV irradiation-induced genome damage. We have recently observed that Pol η is also required for the stability of common fragile sites (CFSs), whose rearrangements are considered a driving force of oncogenesis. Here, we explored the molecular mechanisms underlying this newly identified role. We demonstrated that Pol η accumulated at CFSs upon partial replication stress and could efficiently replicate non-B DNA sequences within CFSs. Pol η deficiency led to persistence of checkpoint-blind under-replicated CFS regions in mitosis, detectable as FANCD2-associated chromosomal sites that were transmitted to daughter cells in 53BP1-shielded nuclear bodies. Expression of a catalytically inactive mutant of Pol η increased replication fork stalling and activated the replication checkpoint. These data are consistent with the requirement of Pol η-dependent DNA synthesis during S phase at replication forks stalled in CFS regions to suppress CFS instability by preventing checkpoint-blind under-replicated DNA in mitosis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Line, Tumor
  • Cell Nucleus / enzymology
  • Chromosome Fragile Sites*
  • Chromosome Fragility
  • DNA Replication
  • DNA, B-Form / genetics
  • DNA-Directed DNA Polymerase / genetics
  • DNA-Directed DNA Polymerase / metabolism*
  • DNA-Directed DNA Polymerase / physiology
  • Homologous Recombination
  • Humans
  • Inverted Repeat Sequences
  • Mitosis
  • Protein Binding
  • S Phase Cell Cycle Checkpoints
  • Stress, Physiological


  • DNA, B-Form
  • DNA-Directed DNA Polymerase
  • Rad30 protein