Integration host factor stimulates both FimB- and FimE-mediated site-specific DNA inversion that controls phase variation of type 1 fimbriae expression in Escherichia coli

Mol Microbiol. 1997 Feb;23(4):705-17. doi: 10.1046/j.1365-2958.1997.2241615.x.


The site-specific DNA inversion that controls phase variation of type 1 fimbriation in E. coli is catalysed by two recombinases, FimB and FimE. Efficient inversion by either recombinase also requires the leucine-responsive regulatory protein (Lrp). In addition, FimB recombination is stimulated by the integration host factor (IHF). The effect of IHF on FimE inversion has not previously been reported. Here it is shown that IHF stimulates FimE recombination; In strain MG1655, mutants containing lesions in either the alpha (ihfA) or beta (ihfB) subunits of IHF show a marked decrease in both FimB- (100-fold) and FimE (15,000-fold)-promoted switching. IHF is shown to bind with high affinity to sites both adjacent to (site I) and within (site II) the fim invertible element. Furthermore, mutations in site I or site II that lower the affinity of IHF binding In vitro were found to lower the frequency of FimE and/ or FimB recombination in vivo. Although site I and site II mutations in combination have an effect on FimB-promoted switching comparable to that of IHF knockout mutations (100-fold), the cis site mutations have a much less marked effect (100-fold) on FimE-promoted switching.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism
  • Base Sequence
  • Binding Sites / genetics
  • DNA Footprinting
  • DNA Primers / genetics
  • DNA, Bacterial / genetics*
  • DNA, Bacterial / metabolism
  • DNA-Binding Proteins / genetics*
  • DNA-Binding Proteins / metabolism
  • Escherichia coli / genetics*
  • Escherichia coli / metabolism
  • Escherichia coli Proteins*
  • Genes, Bacterial
  • Genes, Switch
  • Integrases*
  • Integration Host Factors
  • Models, Genetic
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Mutation
  • Pili, Sex / genetics
  • Pili, Sex / metabolism


  • Bacterial Proteins
  • DNA Primers
  • DNA, Bacterial
  • DNA-Binding Proteins
  • Escherichia coli Proteins
  • Integration Host Factors
  • fimB protein, E coli
  • fimE protein, E coli
  • Integrases