The molecular basis for the specificity of fimE in the phase variation of type 1 fimbriae of Escherichia coli K-12

Mol Microbiol. 1999 Feb;31(4):1171-81. doi: 10.1046/j.1365-2958.1999.01257.x.


The expression of type 1 fimbriae in Escherichia coli is phase variable, with cells switching between fimbriate (ON) and afimbriate (OFF) phases. The phase variation is dependent on the orientation of a 314 bp DNA element (the switch) that undergoes DNA inversion. DNA inversion requires either fimB or fimE, site-specific recombinases that differ in both specificity and activity. Whereas fimB promotes recombination with little orientational bias, fimE promotes recombination in the ON-to-OFF direction exclusively. In wild-type cells, fimE activity predominates and, hence, most bacteria are afimbriate. Here, it is shown that fimE specificity is caused by two different, but complementary, mechanisms. First, FimE shows a strong preference for the switch in the ON orientation as a substrate for recombination. Differences in the nucleotide sequence of the recombinase binding sites is a key factor in determining FimE specificity, although one or more additional cis-active sites that flank the fim switch also appear to be involved. Secondly, the orientation of the switch controls fimE in cis, most probably to control recombinase expression.

Publication types

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

MeSH terms

  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism*
  • Base Sequence
  • Binding Sites
  • DNA Nucleotidyltransferases / metabolism
  • DNA-Binding Proteins / genetics*
  • DNA-Binding Proteins / metabolism*
  • Escherichia coli / genetics
  • Escherichia coli / growth & development
  • Escherichia coli / metabolism*
  • Escherichia coli / ultrastructure*
  • Escherichia coli Proteins*
  • Fimbriae, Bacterial / metabolism*
  • Gene Expression Regulation, Bacterial
  • Genes, Bacterial
  • Genes, Switch
  • Integrases*
  • Molecular Sequence Data
  • Plasmids / genetics
  • Recombinases
  • Recombination, Genetic


  • Bacterial Proteins
  • DNA-Binding Proteins
  • Escherichia coli Proteins
  • Recombinases
  • fimE protein, E coli
  • DNA Nucleotidyltransferases
  • Integrases
  • integron integrase IntI1