Transcriptional regulation of the iron-responsive sigma factor gene pbrA.
In response to the intracellular iron concentration Pseudomonas fluorescens M114 coordinately regulates the production of pseudobactin M114, its cognate receptor PbuA, and a casein protease. Transcriptional initiation of this coordinate iron-stress response requires the sigma factor PbrA. PbrA is a member of the ECF (Extracytoplasmic function) subgroup of the sigma 70 family of eubacterial RNA polymerase sigma factors. Regulatory studies of the pbrA gene utilising promoter-lacZ transcriptional fusions demonstrate that expression of pbrA dictates the cellular response to iron. pbrA is transcribed in all phases of iron-limited growth but maximally at late-logarithmic to stationary phase. pbrA expression is independent of autoregulatory control but is strictly repressed in iron-rich conditions in a Fur-dependent fashion. Constitutive expression of pbrA from an inducible tac promoter permits the induction of PbrA-dependent transcription and pseudobactin M114 biosynthesis in high-iron conditions. A PbrA consensus sequences was derived from significant DNA sequence homologies observed within the "-25 bp" and "-16 bp" regions conserved among all PbrA-dependent promoters. The predicted PbrA target promoter consensus is homologous for the promoter recognition sites for other environmentally responsive ECF sigma factors.
Sexton
R
R
Microbiology Department, University College, Cork, Ireland.
Gill
P R
PR
Dowling
D N
DN
O'Gara
F
F
D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D001483:Base Sequence; D003001:Cloning, Molecular; D016384:Consensus Sequence; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D007501:Iron / Q000378:metabolism; D007763:Lac Operon; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011551:Pseudomonas fluorescens / Q000235:genetics* / Q000378:metabolism; D012689:Sequence Homology, Nucleic Acid; D012808:Sigma Factor / Q000235:genetics*; D015534:Trans-Activators / Q000235:genetics*; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D004269:DNA, Bacterial; C093496:PbrA protein, Pseudomonas fluorescens; D012808:Sigma Factor; D015534:Trans-Activators; D007501:Iron