Abstract
The expression of the inner membrane protein NlpA is repressed by the enterotoxigenic
Escherichia coli
(ETEC) virulence regulator Rns, a member of the AraC/XylS family. The Rns homologs CfaD from ETEC and AggR from enteroaggregative
E. coli
also repress expression of
nlpA
. In vitro DNase I and potassium permanganate footprinting revealed that Rns binds to a site overlapping the start codon of
nlpA
, preventing RNA polymerase from forming an open complex at
nlpAp
. A second Rns binding site between positions −152 and −195 relative to the
nlpA
transcription start site is not required for repression. NlpA is not essential for growth of
E. coli
under laboratory conditions, but it does contribute to the biogenesis of outer membrane vesicles. As outer membrane vesicles have been shown to contain ETEC heat-labile toxin, the repression of
nlpA
may be an indirect mechanism through which the virulence regulators Rns and CfaD limit the release of toxin.
