title: DNA relaxation-dependent phase biasing of the fim genetic switch in Escherichia coli depends on the interplay of H-NS, IHF and LRP.
abstract: Reversible inversion of the DNA element fimS is responsible for the phase variable expression of type 1 fimbriae in Escherichia coli. The FimB tyrosine integrase site-specific recombinase inverts fimS in the on-to-off and off-to-on directions with approximately equal efficiencies. However, when DNA supercoiling is relaxed, fimS adopts predominantly the on orientation. This orientational bias is known to require binding of the nucleoid-associated protein LRP within fimS. Here we show that binding of the IHF protein to a site immediately adjacent to fimS is also required for phase-on orientational bias. In the absence of both LRP and IHF binding, fimS adopts the off orientation and the H-NS protein is required to maintain this alternative orientational bias. Thus, fimS has three Recombination Directionality Factors, H-NS, IHF and LRP. The relevant H-NS binding site straddles the left inverted repeat in phase-off fimS and this site is disrupted when fimS inverts to the on orientation. The inversion of fimS with the associated creation and removal of an H-NS binding site required for DNA inversion biasing represents a novel mechanism for modulating the interaction of H-NS with a DNA target and for influencing a site-specific recombination reaction.
authors.affiliation: Department of Microbiology, Moyne Institute of Preventive Medicine, School of Genetics and Microbiology, Trinity College Dublin, Dublin 2, Ireland.
authors.forename: Colin P
authors.initials: CP
authors.lastname: Corcoran
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Dorman
mesh_terms: D004254:DNA Nucleotidyltransferases / Q000378:metabolism*; D004269:DNA, Bacterial / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D004927:Escherichia coli Infections / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D036781:Fimbriae Proteins / Q000235:genetics / Q000378:metabolism*; D010861:Fimbriae, Bacterial / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D019426:Integrases / Q000378:metabolism; D034982:Integration Host Factors / Q000378:metabolism*; D051756:Leucine-Responsive Regulatory Protein / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D050436:Regulatory Elements, Transcriptional
chemical_list: D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; C529458:FimG protein, E coli; D034982:Integration Host Factors; C497278:Lrp protein, E coli; C440502:integration host factor, E coli; D051756:Leucine-Responsive Regulatory Protein; D036781:Fimbriae Proteins; D004254:DNA Nucleotidyltransferases; D019426:Integrases; C077570:Site-specific recombinase