title: Gated rotation mechanism of site-specific recombination by ϕC31 integrase.
abstract: Integrases, such as that of the Streptomyces temperate bacteriophage ϕC31, promote site-specific recombination between DNA sequences in the bacteriophage and bacterial genomes to integrate or excise the phage DNA. ϕC31 integrase belongs to the serine recombinase family, a large group of structurally related enzymes with diverse biological functions. It has been proposed that serine integrases use a "subunit rotation" mechanism to exchange DNA strands after double-strand DNA cleavage at the two recombining att sites, and that many rounds of subunit rotation can occur before the strands are religated. We have analyzed the mechanism of ϕC31 integrase-mediated recombination in a topologically constrained experimental system using hybrid "phes" recombination sites, each of which comprises a ϕC31 att site positioned adjacent to a regulatory sequence recognized by Tn3 resolvase. The topologies of reaction products from circular substrates containing two phes sites support a right-handed subunit rotation mechanism for catalysis of both integrative and excisive recombination. Strand exchange usually terminates after a single round of 180° rotation. However, multiple processive "360° rotation" rounds of strand exchange can be observed, if the recombining sites have nonidentical base pairs at their centers. We propose that a regulatory "gating" mechanism normally blocks multiple rounds of strand exchange and triggers product release after a single round.
authors.affiliation: Institute of Molecular, Cell, and Systems Biology,  University of Glasgow, Glasgow G12 8QQ, Scotland,  United Kingdom.
authors.forename: Femi J
authors.initials: FJ
authors.lastname: Olorunniji
authors.forename: Dorothy E
authors.initials: DE
authors.lastname: Buck
authors.forename: Sean D
authors.initials: SD
authors.lastname: Colloms
authors.forename: Andrew R
authors.initials: AR
authors.lastname: McEwan
authors.forename: Margaret C M
authors.initials: MC
authors.lastname: Smith
authors.forename: W Marshall
authors.initials: WM
authors.lastname: Stark
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Rosser
mesh_terms: D001435:Bacteriophages / Q000201:enzymology* / Q000235:genetics; D004279:DNA, Viral / Q000235:genetics; D019426:Integrases / Q000235:genetics / Q000378:metabolism*; D011995:Recombination, Genetic
chemical_list: D004279:DNA, Viral; D019426:Integrases