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Blackwell Science LtdOxford UKMMIMolecular Microbiology0950 382XBlackwell Publishing Ltd 2005 200555618961910Original ArticleM tuberculosis fRv1 integration and excisionL A Bibb M I Hancox and G F Hatfull Molecular Microbiology 2005 55 6 1896 1910 doi 10 1111 j 1365 2958 2005 04517 x Integration and excision by the large serine recombinase fRv1 integrase Lori A Bibb Maria I Hancox and Graham F Hatfull Pittsburgh Bacteriophage Institute and Department of Biological Sciences University of Pittsburgh Pittsburgh PA 15260 USA Summary The Mycobacterium tuberculosis prophage like element fRv1 encodes a site specific recombination system utilizing an integrase of the serine recombinase family Recombination occurs between a putative attP site and the host chromosome but is unusual in that the attB site lies within a redundant repetitive element REP13E12 of which there are seven copies in the M tuberculosis genome four of these elements contain attB sites suitable for fRv1 integration in vivo Although the mechanism of directional control of large serine integrases is poorly understood a recombination directionality factor RDF has been identified that is required for fRv1 integrase mediated excisive recombination in vivo Here we describe defined in vitro recombination reactions for both fRv1 integrase mediated integration and excision and show that the fRv1 RDF is not only required for excision but inhibits integrative recombination neither reaction requires DNA supercoiling host factors or high energy cofactors Integration excision and excise mediated inhibition of integration require simple substrates sites indicating that the control of directionality does not involve the manipulation of higher order protein DNA architectures as described for the tyrosine integrases Introduction The genomes of both Mycobacterium tuberculosis H37Rv and CDC1551 contain two prophage like elements fRv1 and fRv2 and while related elements are present in Mycobacterium bovis AF2122 97 Cole et al

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