The AddAB helicase-nuclease catalyses rapid and processive DNA unwinding using a single Superfamily 1A motor domain

Nucleic Acids Res. 2011 Mar;39(6):2271-85. doi: 10.1093/nar/gkq1124. Epub 2010 Nov 10.


The oligomeric state of Superfamily I DNA helicases is the subject of considerable and ongoing debate. While models based on crystal structures imply that a single helicase core domain is sufficient for DNA unwinding activity, biochemical data from several related enzymes suggest that a higher order oligomeric species is required. In this work we characterize the helicase activity of the AddAB helicase-nuclease, which is involved in the repair of double-stranded DNA breaks in Bacillus subtilis. We show that the enzyme is functional as a heterodimer of the AddA and AddB subunits, that it is a rapid and processive DNA helicase, and that it catalyses DNA unwinding using one single-stranded DNA motor of 3' → 5' polarity located in the AddA subunit. The AddB subunit contains a second putative ATP-binding pocket, but this does not contribute to the observed helicase activity and may instead be involved in the recognition of recombination hotspot sequences.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Motifs
  • Biocatalysis
  • DNA / metabolism*
  • DNA Helicases / chemistry
  • DNA Helicases / genetics
  • DNA Helicases / metabolism*
  • DNA, Single-Stranded / metabolism
  • Dimerization
  • Exodeoxyribonucleases / chemistry
  • Exodeoxyribonucleases / genetics
  • Exodeoxyribonucleases / metabolism*
  • Mutation
  • Protein Structure, Tertiary
  • Protein Subunits / metabolism


  • DNA, Single-Stranded
  • Protein Subunits
  • DNA
  • Exodeoxyribonucleases
  • AddAB enzyme
  • DNA Helicases