FUNCTIONAL INTERACTIONS BETWEEN THE HOLLIDAY JUNCTION RESOLVASE AND THE BRANCH MIGRATION MOTOR OF ESCHERICHIA-COLI

Homologous recombination generates genetic diversity and provides an i mportant cellular pathway for the repair of double-stranded DNA breaks , Two key steps in this process are the branch migration of Holliday j unctions followed by their resolution into mature recombination produc ts. In E. coli, branch migration is catalysed by the RuvB protein, a h exameric DNA helicase that is loaded onto the junction by RuvA, wherea s resolution is promoted by the RuvC endonuclease. Here we provide dir ect evidence for functional interactions between RuvB and RuvC that li nk these biochemically distinct processes. Using synthetic Holliday ju nctions, RuvB was found to stabilize the binding of RuvC to a junction and to stimulate its resolvase activity. Conversely, RuvC facilitated interactions between RuvB and the junction such that RuvBC complexes catalysed branch migration. The observed synergy between RuvB and RuvC provides new insight into the structure and function of a RuvABC comp lex that is capable of facilitating branch migration and resolution of Holliday junctions via a concerted enzymatic mechanism.