title: Leucine-responsive regulatory protein plays dual roles as both an activator and a repressor of the Escherichia coli pap fimbrial operon.
abstract: The expression of the pap pilus operon of Escherichia coli is under a phase-variation control mechanism in which cells undergo a reversible transition between transcriptionally active (phase ON) and inactive (phase OFF) states. In this study, we explore the roles of leucine-responsive regulatory protein (Lrp) and the histone-like protein H-NS in the regulation of pap phase variation. Our data indicate that the phase OFF state results from repression of the intrinsically active papBA promoter by Lrp and H-NS, each of which can act independently as transcriptional repressors. Lrp requires pap DNA sequences upstream of the papBA promoter for its repressor activity whereas H-NS does not. In contrast, in the ON state, Lrp, in conjunction with PapI, activates pap transcription. This activation is not merely a result of alleviating the H-NS mediated repression, but induces a level of transcription that is eightfold higher than the basal level of transcription from the papBA promoter measured in the absence of both H-NS and Lrp. Analysis of Lrp activation mutants indicates that binding of Lrp to pap DNA sequences is not sufficient for transcription activation, consistent with a model in which an additional domain of Lrp interacts with the transcriptional apparatus. Together, our results show that Lrp functions as a transcriptional activator in phase-ON cells and as a repressor of basal transcription in phase-OFF cells. Because pap phase variation occurs in the absence of H-NS, it is not clear what role this regulatory protein plays in pap gene regulation.
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000502:physiology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D001483:Base Sequence; D004269:DNA, Bacterial / Q000378:metabolism; D004274:DNA, Recombinant; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D004926:Escherichia coli / Q000235:genetics* / Q000502:physiology; D029968:Escherichia coli Proteins; D010861:Fimbriae, Bacterial / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D051756:Leucine-Responsive Regulatory Protein; D008969:Molecular Sequence Data; D009154:Mutation; D009876:Operon / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D017384:Sequence Deletion; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014157:Transcription Factors; D014158:Transcription, Genetic / Q000235:genetics
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004274:DNA, Recombinant; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C031908:H-NS protein, bacteria; C497278:Lrp protein, E coli; C086707:PapI protein, E coli; D012097:Repressor Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D051756:Leucine-Responsive Regulatory Protein