CRYSTAL-STRUCTURE OF ESCHERICHIA-COLI RUVA WITH BOUND DNA HOLLIDAY JUNCTION AT 6 ANGSTROM RESOLUTION

Here we present the crystal structure of the Escherichia coli protein RuvA bound to a key DNA intermediate in recombination, the Holliday ju nction. The structure, solved by isomorphous replacement and density m odification at 6 Angstrom resolution, reveals the molecular architectu re at the heart of the branch migration and resolution reactions requi red to process Holliday intermediates into recombinant DNA molecules, It also reveals directly for the first time the structure of the Holli day junction, A. single RuvA tetramer is bound to one face of a juncti on whose four DNA duplex arms are arranged in an open and essentially four-fold symmetric conformation. Protein-DNA contacts are mediated by two copies of a helix-hairpin-helix motif per RuvA subunit that conta ct the phosphate backbone in a very similar manner. The open structure of the junction stabilized by RuvA binding exposes a DNA surface that could be bound by the RuvC endonuclease to promote resolution.