title: Identification of the promoter and a negative regulatory element, ftr4, that is needed for cell cycle timing of fliF operon expression in Caulobacter crescentus.
abstract: The fliF operon of Caulobacter crescentus, which was previously designated the flaO locus, is near the top of the flagellar-gene regulatory hierarchy, and it is one of the earliest transcription units to be expressed in the cell cycle. In this report, we have identified two cis-acting sequences that are required for cell cycle regulation of fliF transcription. The first sequence was defined by the effects of three 2-bp deletions and five point mutations, each of which greatly reduced the level of fliF operon transcript in vivo. These eight mutations lie between -37 and -22 within an 18-bp sequence that matches, at 11 nucleotides, sequences in the 5' regions of the flaQR (flaS locus) and fliLM operons, which are also expressed early and occupy a high level in the regulatory hierarchy (A. Dingwall, A. Zhuang, K. Quon, and L. Shapiro, J. Bacteriol. 174:1760-1768, 1992). We propose that this 18-bp sequence contains all or part of the fliF promoter. We have also identified a second sequence, 17 bp long and centered at -8, which we have provisionally designated ftr4 because of its similarity to the enhancer-like ftr sequences required for regulation of sigma 54 promoters flaN and flbG (D. A. Mullin and A. Newton, J. Bacteriol. 171:3218-3227, 1989). Six of the seven mutations in ftr4 examined resulted in a large increase in fliF operon transcript levels, suggesting a role for ftr4 in negative regulation. A 2-bp deletion at -12 and -13 in ftr4 altered the cell cycle pattern of fliF operon transcription; the transcript was still expressed periodically, but the period of its synthesis was extended significantly. We suggest that the ftr4 sequence may form part of a developmental switch which is required to turn off fliF operon transcription at the correct time in the cell cycle.
authors.affiliation: Department of Cell and Molecular Biology, Tulane University, New Orleans, Louisiana 70118-5698.
authors.forename: S M
authors.initials: SM
authors.lastname: Van Way
authors.forename: A
authors.initials: A
authors.lastname: Newton
authors.forename: A H
authors.initials: AH
authors.lastname: Mullin
authors.forename: D A
authors.initials: DA
authors.lastname: Mullin
mesh_terms: D001483:Base Sequence; D016935:Caulobacter crescentus / Q000235:genetics*; D002453:Cell Cycle / Q000235:genetics*; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D004742:Enhancer Elements, Genetic; D004926:Escherichia coli / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009838:Oligodeoxyribonucleotides; D009876:Operon; D010957:Plasmids; D011401:Promoter Regions, Genetic; D012045:Regulatory Sequences, Nucleic Acid; D015183:Restriction Mapping; D012689:Sequence Homology, Nucleic Acid; D014158:Transcription, Genetic
chemical_list: D009838:Oligodeoxyribonucleotides; D015500:Chloramphenicol O-Acetyltransferase