The chi (v)and psi(w) subunits of Escherichia coliDNA polymerase III formaheterodimer that is associatedwith the ATP-dependent clamp-loadermachinery. InE. coli,thev:w heterodimer serves as a bridge between the clamp-loader complex and the single-strandedDNA-binding protein. We determined the crystal structure of thev:wheterodimer at A ˚ resolution. Although neitherv(147 residues) nor w (137 residues) bind to nucleotides, the fold of each protein is similar to the folds of mononucleotide-(v) or dinucleotide-(w) binding proteins, without marked similarity to the structures of the clamp-loader subunits
