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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
Author(s) -
Blomfield Ian C.,
Kulasekara Don H.,
Eisenstein Barry I.
Publication year - 1997
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.1997.2241615.x
Subject(s) - phase variation , recombinase , biology , recombination , binding site , mutant , dna , escherichia coli , genetics , site specific recombination , a site , homologous recombination , microbiology and biotechnology , gene , virulence
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 α ( ihfA ) or β ( 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.