Ring structure of the Escherichia coli DNA-binding protein RdgC associated with recombination and replication fork repair

The DNA-binding protein, RdgC, is associated with recombination and replication fork repair in Escherichia coli and with the virulence- associated, pilin antigenic variation mediated by RecA and other recombination proteins in Neisseria species. We solved the structure of the E. coli protein and refined it to 2.4 angstrom. RdgC crystallizes as a dimer with a head-to-head, tail-to-tail organization forming a ring with a 30 angstrom diameter hole at the center. The protein fold is unique and reminiscent of a horseshoe with twin gates closing the open end. The central hole is lined with positively charged residues and provides a highly plausible DNA binding channel consistent with the nonspecific mode of binding detected in vitro and with the ability of RdgC to modulate RecA function in vivo.