Structure of RecJ exonuclease defines its specificity for single-stranded DNA.

RecJ is a single-stranded DNA (ssDNA)-specific 5'-3' exonuclease that plays an important role in DNA repair and recombination. To elucidate how RecJ achieves its high specificity for ssDNA, we determined the entire structures of RecJ both in a ligand-free form and in a complex with Mn(2+) or Mg(2+) by x-ray crystallography. The entire RecJ consists of four domains that form a molecule with an O-like structure.