title: RuvAB-mediated branch migration does not involve extensive DNA opening within the RuvB hexamer.
abstract: The Escherichia coli RuvA and RuvB proteins promote the branch migration of Holliday junctions during the late stages of homologous recombination and DNA repair (reviewed in [1]). Biochemical and structural studies of the RuvAB-Holliday junction complex have shown that RuvA binds directly to the Holliday junction [2] [3] [4] [5] [6] and acts as a specificity factor that promotes the targeting of RuvB [7] [8], a hexameric ring protein that drives branch migration [9] [10] [11]. Electron microscopic visualisation of the RuvAB complex revealed that RuvA is flanked by two RuvB hexamers, which bind DNA arms that lie diametrically opposed across the junction [8]. ATP-dependent branch migration occurs as duplex DNA is pumped out through the centre of each ring. Because RuvB possesses well-conserved helicase motifs and RuvAB exhibits a 5'-3' DNA helicase activity in vitro [12], the mechanism of branch migration is thought to involve DNA opening within the RuvB ring, which provides a single strand for the unidirectional translocation of the protein along DNA. We have investigated whether the RuvB ring can translocate along duplex DNA containing a site-directed interstrand psoralen crosslink. Surprisingly, we found that the crosslink failed to inhibit branch migration. We interpret these data as evidence against a base-by-base tracking model and suggest that extensive DNA opening within the RuvB ring is not required for DNA translocation by RuvB.
authors.affiliation: Clare Hall Laboratories, Imperial Cancer Research Fund, South Mimms, EN6 3LD, UK.
authors.forename: H
authors.initials: H
authors.lastname: George
authors.forename: I
authors.initials: I
authors.lastname: Kuraoka
authors.forename: D A
authors.initials: DA
authors.lastname: Nauman
authors.forename: W R
authors.initials: WR
authors.lastname: Kobertz
authors.forename: R D
authors.initials: RD
authors.lastname: Wood
authors.forename: S C
authors.initials: SC
authors.lastname: West
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000502:physiology*; D001704:Biopolymers; D004247:DNA / Q000737:chemistry / Q000235:genetics; D004265:DNA Helicases; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000502:physiology*; D029968:Escherichia coli Proteins; D006868:Hydrolysis; D011995:Recombination, Genetic
chemical_list: D001426:Bacterial Proteins; D001704:Biopolymers; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C061260:RuvB protein, Bacteria; D000255:Adenosine Triphosphate; D004247:DNA; C071059:Holliday junction DNA helicase, E coli; D004265:DNA Helicases