A crystal structure of the C-terminal domain of Escherichia coli UvrB (UvrB′) has been solved to 3.0 Å resolution. The domain adopts a helix-loop-helix fold which is stabilised by the packing of hydrophobic side-chains between helices. From the UvrB′ fold, a model for a domain of UvrC (UvrC′) that has high sequence homology with UvrB′ has been made. In the crystal, a dimerisation of UvrB′ domains is seen involving specific hydrophobic and salt bridge interactions between residues in and close to the loop region of the domain. It is proposed that a homologous mode of interaction may occur between UvrB and UvrC. This interaction is likely to be flexible, potentially spanning >50 Å.
