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Leucine‐responsive regulatory protein plays dual roles as both an activator and a repressor of the Escherichia coli pap fimbrial operon
Author(s) -
Woude M. W.,
Kaltenbach L.S.,
Low D.A.
Publication year - 1995
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 - 10.1111/j.1365-2958.1995.mmi_17020303.x
Subject(s) - biology , operon , repressor , activator (genetics) , escherichia coli , l arabinose operon , leucine , lac operon , trp operon , microbiology and biotechnology , dual (grammatical number) , gene , genetics , transcription factor , amino acid , art , literature
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 Papl, 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.