The Leucine-Responsive Regulatory Protein, Lrp, Activates Transcription of thefimOperon inSalmonella entericaSerovar Typhimurium via thefimZRegulatory Gene

Abstract

The fim operon of Salmonella enterica serovar Typhimurium encodes type 1 fimbriae. The expression of fim is controlled in response to environmental signals through a complex regulatory cascade involving the proteins FimW, FimY, and FimZ and a genetic locus, fimU, that encodes a rare arginine tRNA. We discovered that a knockout mutation in lrp, the gene that codes for the leucine-responsive regulatory protein (Lrp), inhibited fim transcription. The loss of fim gene expression was accompanied by a corresponding loss of the mannosesensitive hemagglutination that is a characteristic of type 1 fimbriae. Normal type 1 fimbrial expression was restored following the introduction into the knockout mutant of a plasmid carrying a functional copy of the lrp gene. Electrophoretic mobility shift analysis revealed no interactions between purified Lrp protein and the regulatory region of the fimA, fimU, or fimW gene. Instead, Lrp produced protein-DNA complexes with the regulatory region of the fimZ gene, and the nature of these complexes was leucine sensitive. DNase I footprinting showed that Lrp binds within a region between ؊65 and ؊170 with respect to the fimZ transcription start site, consistent with the binding and wrapping of the DNA in this upstream region. Ectopic expression of the fimZ gene from an inducible promoter caused Lrp-independent type 1 fimbriation in serovar Typhimurium. These data show that Lrp makes a positive contribution to fim gene expression through direct interaction with the fimZ promoter region, possibly by antagonizing the binding of the H-NS global repressor protein.

Regulation of Expression of Uropathogenic Escherichia coli Nonfimbrial Adhesin TosA by PapB Homolog TosR in Conjunction with H-NS and Lrp

“…An H-NS and Lrp regulatory switch drives tos operon transcriptional regulation. It has been previously proposed and noted that Lrp might act to anti-silence H-NS repression (35,38,59,68). We hypothesize, therefore, that an H-NS and Lrp regulation switch (i.e., predominance of either H-NS or Lrp) explains the observed regulation of the tos operon.…”

“…In agreement with this, others have noted the possibility that Lrp and H-NS antagonize the activity of each other or could interact together to potentiate gene regulation (35,38,59,68). This type of regulation resembles a regulatory switch, in which one nucleoid-structuring protein switches in predominance at key regulatory elements to perturb gene regulation.…”

“…Coupled with the finding that TosR regulation is abolished in the ⌬lrp background, these results suggest that an H-NS and Lrp regulation switch likely contributes to tos operon regulation, and TosR has a function within this regulatory switch. It is important to note, however, that both H-NS and Lrp are global regulators (19,22,(37)(38)(39)(59)(60)(61)(62)(63)(64)(65)(66)(67). Therefore, it cannot be ruled out that regulation between H-NS and Lrp, at P tos is indirect.…”

“…Likewise, a shift to a lower antibiotic concentration for the ⌬hns and ⌬lrp backgrounds harboring pBAD-tosR-His 6 does not perturb TosR regulation itself; the lower antibiotic concentration did not perturb TosR-mediated regulation in the wild-type E. coli CFT073 background (data not shown). As for H-NS, Lrp is also a global regulator (19,22,(37)(38)(39)(59)(60)(61)(62)(63)(64)(65)(66)(67). Therefore, it remains unclear if additional gene products also supplement Lrp-and TosRmediated positive regulation of the tos operon.…”

More than One Way To Control Hair Growth: Regulatory Mechanisms in Enterobacteria That Affect Fimbriae Assembled by the Chaperone/Usher Pathway

“…Rao and colleagues (75) suggested that type 1 fimbrial expression is controlled by a positive feedback loop involving FimY and FimZ as well as a negative feedback loop between FimW and FimY. In addition, the expression of fimZ itself has been shown to be controlled at the level of transcription by Lrp, and Lrp-negative mutants show no fim expression (59). Lrp binds to a region upstream (between bp 65 and 170) of the fimZ transcription start site and is proposed to facilitate fimZ expression, leading to increased type 1 fimbrial production due to activation by FimZ.…”