title: Single-molecule analysis reveals the molecular bearing mechanism of DNA strand exchange by a serine recombinase.
abstract: Structural and topological data suggest that serine site-specific DNA recombinases exchange duplex DNAs by rigid-body relative rotation of the two halves of the synapse, mediated by a flat protein-protein interaction surface. We present evidence for this rotational motion for a simple serine recombinase, the Bxb1 phage integrase, from a single-DNA-based supercoil-release assay that allows us to follow crossover site cleavage, rotation, religation, and product release in real time. We have also used a two-DNA braiding-relaxation experiment to observe the effect of synapse rotation in reactions on two long molecules. Relaxation and unbraiding are rapid (averaging 54 and 70 turns/s, respectively) and complete, with no discernible pauses. Nevertheless, the molecular friction associated with rotation is larger than that of type-I topoisomerases in a similar assay. Surprisingly we find that the synapse can stay rotationally "open" for many minutes.
authors.affiliation: Department of Physics, University of Illinois at Chicago, Chicago, IL 60607, USA.
authors.forename: Hua
authors.initials: H
authors.lastname: Bai
authors.forename: Mingxuan
authors.initials: M
authors.lastname: Sun
authors.forename: Pallavi
authors.initials: P
authors.lastname: Ghosh
authors.forename: Graham F
authors.initials: GF
authors.lastname: Hatfull
authors.forename: Nigel D F
authors.initials: ND
authors.lastname: Grindley
authors.forename: John F
authors.initials: JF
authors.lastname: Marko
mesh_terms: D001710:Biotin; D004254:DNA Nucleotidyltransferases / Q000378:metabolism*; D004278:DNA, Superhelical / Q000737:chemistry / Q000378:metabolism*; D004076:Digoxigenin; D004926:Escherichia coli / Q000235:genetics; D010957:Plasmids / Q000235:genetics; D012399:Rotation; D012694:Serine / Q000378:metabolism*
chemical_list: D004278:DNA, Superhelical; D012694:Serine; D001710:Biotin; D004254:DNA Nucleotidyltransferases; C077570:Site-specific recombinase; D004076:Digoxigenin