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The molecular basis for the specificity of fimE in the phase variation of type 1 fimbriae of Escherichia coli K‐12
Author(s) -
Kulasekara Hemantha Don,
Blomfield Ian C.
Publication year - 1999
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.1365-2958.1999.01257.x
Subject(s) - biology , fimbria , escherichia coli , phase variation , variation (astronomy) , type (biology) , microbiology and biotechnology , computational biology , genetics , virulence , gene , ecology , physics , astrophysics
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.