The molecular basis for the specificity of fimE in the phase variation of type 1 fimbriae of Escherichia coli K-12.
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.
Kulasekara
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Department of Microbiology and Immunology, Wake Forest University School of Medicine, Winston-Salem, NC 27157-1064, USA.
Blomfield
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IC
D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D004254:DNA Nucleotidyltransferases / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000378:metabolism* / Q000648:ultrastructure*; D029968:Escherichia coli Proteins; D010861:Fimbriae, Bacterial / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D005812:Genes, Switch; D019426:Integrases; D008969:Molecular Sequence Data; D010957:Plasmids / Q000235:genetics; D045522:Recombinases; D011995:Recombination, Genetic
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D045522:Recombinases; C081955:fimE protein, E coli; D004254:DNA Nucleotidyltransferases; D019426:Integrases; C115006:integron integrase IntI1