DNA relaxation‐dependent phase biasing of the fim genetic switch in Escherichia coli depends on the interplay of H‐NS, IHF and LRP

Abstract

SummaryReversible 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.

PecS regulates the urate-responsive expression of type 1 fimbriae in Klebsiella pneumoniae CG43

“…E. coli HNS binds to fimS-IRL (inverted repeat left) which influences site-specific recombination and thus decreases fimA promoter activity (O'Gara & Dorman, 2000;Corcoran & Dorman, 2009). We have shown that the expression of hns is increased by PecS (Fig.…”

“…The fimS switch, which alternates bacteria between type 1 fimbriated and non-fimbriated states, is controlled by site-specific recombinases FimB and FimE (McClain et al, 1991). The interplay of DNA binding proteins HNS, IHF and Lrp also influences the fimS orientation (Corcoran & Dorman, 2009). Originally characterized in Klebsiella strains, type 3 fimbriae provide the bacteria with the ability to adhere to epithelial cells of the respiratory and urinary tracts (Hornick et al, 1992;Tarkkanen et al, 1997;Jagnow & Clegg, 2003).…”

The regulatory role of DNA supercoiling in nucleoprotein complex assembly and genetic activity

“…This might also apply to integrative recombination catalyzed by the phage λ integrase (Thompson et al 1988;Crisona et al 1999), as well as other reactions catalyzed by the members of integrase superfamily of site-specific recombinases (Abremski and Hoess 1985;Dove and Dorman 1994;Corcoran and Dorman 2009). On the other hand, the recombination by C-terminally-modified SSV1 virus integrase from a thermophilic archaeon characterized by positively supercoiled DNA is more efficient with fully relaxed/linear DNA substrates, and is also directionally highly promiscuous in vitro (Muskhelishvili et al 1993), implicating additional, presently unknown, factors in imparting directionality on the SSV1 integrase-driven recombination in vivo (Schleper et al 1992).…”

The type 1 pili regulator gene fimX and pathogenicity island PAI-X as molecular markers of uropathogenic Escherichia coli

“…Corroborating the molecular pathogenesis studies of type 1 pili in UTI, vaccination with pili subcomponents in animal studies has been shown to reduce the severity and duration of infection (Palaszynski et al, 1998). Type 1 pili are encoded by the fim operon (fimAICDFGH) and their expression is controlled at multiple regulatory levels (Corcoran & Dorman, 2009;Kelly et al, 2006;McClain et al, 1991). The orientation of the invertible type 1 pili promoter region (fimS) (Abraham et al, 1985) is determined by the action of multiple tyrosine recombinases.…”