Activation of a temporally regulated Caulobacter promoter by upstream and downstream sequence elements.
The flagellar genes of Caulobacter crescentus are expressed under cell-cycle control. Expression is regulated by both flagellar assembly cues and cell-cycle events. In this paper we define the sequences required for the expression of the flgF operon, a new class of sigma 54 flagellar promoter. This promoter type is expressed in the middle portion of the cell cycle and regulates the expression of basal-body genes. DNase I footprinting and mutagenesis demonstrates that an integration host factor (IHF)-binding site is required for maximal levels of transcription of the flgF promoter. In addition to containing a conventional upstream enhancer element (RE-1), this promoter is unusual in that it also requires sequences (element RE-2) immediately downstream of the transcriptional start site for maximal levels of gene expression. Cell-cycle experiments indicate that RE-1 and RE-2 contribute equally to the regulation of temporal transcription. The presence of two intact elements in the promoter results in a fourfold increase in promoter activity compared with a promoter containing only one intact element, suggesting that these two elements may function synergistically to activate transcription.
Marques
M V
MV
Department of Chemistry and Biochemistry, University of California, Los Angeles 90024-1569, USA.
Gober
J W
JW
D001483:Base Sequence; D016935:Caulobacter crescentus / Q000235:genetics*; D002453:Cell Cycle; D004269:DNA, Bacterial / Q000032:analysis*; D004742:Enhancer Elements, Genetic; D005407:Flagella / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D008957:Models, Genetic; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009876:Operon; D011401:Promoter Regions, Genetic; D012045:Regulatory Sequences, Nucleic Acid
D004269:DNA, Bacterial