['Crystallographic and mutational studies of Escherichia coli RuvC Holliday junction resolvase have revealed that a catalytic site of each subunit is composed of four acidic residues at the bottom of the putative DNA-binding cleft, whose surface contains eight basic residues.', 'To elucidate the functional roles of the basic residues on the cleft surface, we constructed a series of mutant ruvC genes and characterized their properties in vivo and in vitro. Among them, two RuvC mutants with a single alteration, K107A and K118A, were defective in UV-repair and showed a dominant negative effect. The purified K107A and K118A proteins showed reduced binding activity to the junction DNA in the presence of Mg2+ under high salt conditions. Mn2+ increased both the junction binding and cleaving activities of the mutant proteins. In the absence of a divalent cation, the wild-type, K107A and K118A proteins did not bind to junction DNA under high salt conditions, but the D7N mutant, with an alteration of the catalytic centre, was able to bind to the junction efficiently.'] Are two basic residues , Lys-107 and Lys-118 , of RuvC resolvase involved in critical contacts with the Holliday junction for its resolution?