Human exonuclease 1 and BLM helicase interact to resect DNA and initiate DNA repair

Proc Natl Acad Sci U S A. 2008 Nov 4;105(44):16906-11. doi: 10.1073/pnas.0809380105. Epub 2008 Oct 29.


The error-free repair of double-stranded DNA breaks by homologous recombination requires processing of broken ends. These processed ends are substrates for assembly of DNA strand exchange proteins that mediate DNA strand invasion. Here, we establish that human BLM helicase, a member of the RecQ family, stimulates the nucleolytic activity of human exonuclease 1 (hExo1), a 5'-->3' double-stranded DNA exonuclease. The stimulation is specific because other RecQ homologs fail to stimulate hExo1. Stimulation of DNA resection by hExo1 is independent of BLM helicase activity and is, instead, mediated by an interaction between the 2 proteins. Finally, we show that DNA ends resected by hExo1 and BLM are used by human Rad51, but not its yeast or bacterial counterparts, to promote homologous DNA pairing. This in vitro system recapitulates initial steps of homologous recombination and provides biochemical evidence for a role of BLM and Exo1 in the initiation of recombinational DNA repair.

Publication types

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

MeSH terms

  • Adenosine Triphosphatases / metabolism
  • DNA / chemistry
  • DNA / metabolism*
  • DNA Breaks, Double-Stranded
  • DNA Helicases / chemistry
  • DNA Helicases / genetics
  • DNA Helicases / metabolism*
  • DNA Repair Enzymes / chemistry
  • DNA Repair Enzymes / metabolism*
  • DNA Repair*
  • Exodeoxyribonucleases / chemistry
  • Exodeoxyribonucleases / metabolism*
  • Humans
  • Rad51 Recombinase / metabolism
  • RecQ Helicases / metabolism
  • Recombination, Genetic
  • Replication Protein A / metabolism


  • Replication Protein A
  • DNA
  • Rad51 Recombinase
  • EXO1 protein, human
  • Exodeoxyribonucleases
  • Adenosine Triphosphatases
  • Bloom syndrome protein
  • DNA Helicases
  • RecQ Helicases
  • DNA Repair Enzymes