In Escherichia coli, the RuvA, RuvB and RuvC proteins are required for the late stages of homologous recombination and DNA repair. RuvA and RuvB form a complex that interacts with Holliday junctions--crossed DNA structures that are recombination intermediates--and promotes branch migration; RuvC is a junction-specific endonuclease that resolves Holliday junctions and completes the recombination process. Because genetic and biochemical experiments suggest that the processes of branch migration and resolution are linked, coimmunoprecipitation experiments were carried out to determine whether the three Ruv proteins interact to form a functional complex (RuvABC). Using a synthetic Holliday junction, a multisubunit complex containing the junction and RuvA, RuvB and RuvC was detected. In the absence of RuvB, RuvAC-junction complexes were observed. Complex formation was not facilitated by duplex DNA. The identification of a RuvABC-junction complex provides direct evidence that the RuvABC proteins interact at the Holliday junction.