title: Linking structural assembly to gene expression: a novel mechanism for regulating the activity of a sigma54 transcription factor.
abstract: In Caulobacter crescentus, the temporal and spatial expression of late flagellar genes is regulated by the sigma54 transcriptional activator, FlbD. Genetic experiments have indicated that the trans-acting factor FliX regulates FlbD in response to the progression of flagellar assembly, repressing FlbD activity until an early flagellar basal body structure is assembled. Following assembly of this structure, FliX is thought to function as an activator of FlbD. Here we have investigated the mechanism of FliX-mediated regulation of FlbD activity. In vitro transcription experiments showed that purified FliX could function as a repressor of FlbD-activated transcription. Transcription activated by a gain-of-function mutant of FlbD (FlbD-1204) that is active in vivo in the absence of an early flagellar structure, was resistant to the repressive effects of FliX. DNA binding studies showed that FliX inhibited the interaction of wild-type FlbD with enhancer DNA but did not effect FlbD-catalysed ATPase activity. DNA binding activity of FlbD-1204 was relatively unaffected by FliX indicating that this mutant protein bypasses the transcriptional requirement for early flagellar assembly by escaping FliX-mediated negative regulation. Gel filtration and co-immunoprecipitation experiments indicated that FliX formed a stable complex with FlbD. These experiments demonstrate that regulation of FlbD activity is unusual among the well-studied sigma54 transcriptional activators, apparently combining a two-component receiver domain with additional control imposed via interaction with a partner protein, FliX.
authors.affiliation: Department of Chemistry and Biochemistry and Molecular Biology Institute, University of California, Los Angeles, CA 90095-1569, USA.
authors.forename: Rachel J
authors.initials: RJ
authors.lastname: Dutton
authors.forename: Zhaohui
authors.initials: Z
authors.lastname: Xu
authors.forename: James W
authors.initials: JW
authors.lastname: Gober
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D016935:Caulobacter crescentus / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004742:Enhancer Elements, Genetic; D005407:Flagella / Q000235:genetics / Q000502:physiology*; D015964:Gene Expression Regulation, Bacterial; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D046912:Multiprotein Complexes; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D051877:RNA Polymerase Sigma 54 / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C089631:FlbD protein, Caulobacter crescentus; C111943:FliX protein, Caulobacter crescentus; D008565:Membrane Proteins; D046912:Multiprotein Complexes; D051877:RNA Polymerase Sigma 54; D000251:Adenosine Triphosphatases