Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.7.6 (RNA polymerase)
 34,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Transcription of the ferric citrate transport system of Escherichia coli K-12 is repressed by Fe(2+)-Fur and activated by ferric citrate. Ferric citrate does not have to enter the cytoplasm; it initiates a signal transduction mechanism by binding to the outer membrane receptor FecA. Presumably, a conformational change is transmitted in a TonB-dependent manner to the FecR protein. FecR activates FecI, and FecI activates transcription of the fecABCDE transport genes. In this communication, FecI was isolated after cloning fecI downstream of an ideal ribosome-binding site. Overexpressed FecI formed inclusion bodies which were solubilized and purified in active form using a mild detergent. FecI, in conjunction with RNA polymerase core enzyme, directed transcription from the fecA promoter in an in vitro run-off transcription assay. Furthermore, FecI retarded the electrophoretic mobility of a specific 75 bp DNA fragment located upstream of fecA. An in vivo competition experiment between the fecA promoters of wild-type and mutant strains identified the nucleotide positions 2747, 2749, 2751 and 2753, located within the 75 bp fragment, as important for FecI-induced transcription. Mobility band shift of fecA promoter DNA caused by cell lysates required growth of cells in the presence of ferric citrate and expression of FecA, FecI and FecR. These data support the previous assignment of FecI, based on sequence homologies, to a new subfamily of eubacterial RNA polymerase sigma 70 factors that respond to extra-cytoplasmic stimuli and regulate extracytoplasmic functions.
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PMID:Transcriptional regulation of ferric citrate transport in Escherichia coli K-12. Fecl belongs to a new subfamily of sigma 70-type factors that respond to extracytoplasmic stimuli. 859 56

Ferric citrate induces transcription of the ferric citrate transport genes fecABCDE without entering the cells of Escherichia coli K-12. Point mutants of the outer membrane-receptor protein FecA are affected in induction independent of the FecA transport activity, suggesting that FecA is directly involved in induction. Alignment of FecA with the other ferric siderophore receptors of E. coli reveals an N-terminal extension in FecA that is not found in the receptors whose synthesis is not induced by their cognate ferric siderophores. In this study, we show that excision of the N-terminal region abolished the inducing activity of FecA, but retained its transport activity. Overproduction of the N-terminal FecA fragment inhibited FecA-dependent induction, but not transport. Constitutive expression caused by C-terminally truncated FecR derivatives was not inhibited by the N-terminal FecA fragment. The N-terminal region of FecA was localized in the periplasm, which indicates that FecA probably interacts with FecR, which is involved in signal transduction across the cytoplasmic membrane. Transcription initiation of the fec transport genes required the Ton system, consisting of TonB, ExbB, and ExbD, and was inhibited by carbonylcyanide-m-chlorophenylhydrazone (CCCP) and 2,4-dinitrophenol (DNP), which dissipate the electrochemical potential of the cytoplasmic membrane. fec transcription of mutant fecA4, which displays constitutive fec transcription in the absence of TonB, was not affected by CCCP. The data support a model that proposes initiation of fec transport gene transcription by binding of ferric citrate to FecA. The transcription initiation signal is transferred across the outer membrane through the activity of the Ton system at the expense of the electrochemical potential of the cytoplasmic membrane. The N-terminus of FecA interacts in the periplasm with the C-terminus of FecR, through which the signal is transferred across the cytoplasmic membrane into the cytoplasm, where it increases the activity of the sigma factor Fecl, which then directs the RNA polymerase to the fec promoter upstream of fecA.
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PMID:Transcription induction of the ferric citrate transport genes via the N-terminus of the FecA outer membrane protein, the Ton system and the electrochemical potential of the cytoplasmic membrane. 904 67

Transcription of the ferric citrate transport genes of Escherichia coli is induced by a novel mechanism. Ferric citrate, the inducer, does not have to enter the cytoplasm to initiate transcription. Interaction of ferric citrate with the outer membrane receptor protein FecA induces transcription of the fec transport gene operon consisting of the fecIRABCDE genes. A signal from FecA occupied with ferric citrate is transmitted across the outer membrane into the periplasm with the help of the electrochemical potential of the cytoplasmic membrane and the Ton system. The signal is then transduced across the cytoplasmic membrane by the FecR protein, which in turn activates the FecI sigma-factor that directs the RNA polymerase core-enzyme to the fec transport gene promoter. The promoter of the regulatory genes fecI and fecR is not controlled by ferric citrate but is regulated by iron via the Fur repressor. It is proposed that the information flux from the cell surface to the cytoplasm involves a series of conformational changes of the proteins FecA, FecR, and FecI in that order. The level of the regulatory proteins FecI and FecR is adjusted to the intracellular iron concentration and determines the degree of the response of the cell to ferric citrate in the medium. Ferric citrate induces transcription of the fec transport genes under iron-limiting conditions. A regulatory device similar to the ferric citrate transport system exists in Pseudomonas putida WCS358. The synthesis of the outer membrane receptor PupB, involved in the transport of the ferric pseudobactins BN7 and BN8, is induced by the ferric siderophores and requires PupB and two proteins homologous to FecI and FecR.
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PMID:Surface signaling: novel transcription initiation mechanism starting from the cell surface. 914 73

Ferric citrate induces transcription of the ferric citrate transport genes fecABCDE in Escherichia coli by binding to the outer-membrane receptor protein FecA without entering the cell. Replete iron concentrations inhibit transcription of the fec transport system via the iron-loaded Fur repressor. Here we show that the Fur repressor activated by Mn2+ (used instead of Fe2+) binds to the promoter of the regulatory genes fecIR and to the promoter of fecABCDE. DNase I footprint analysis revealed that Mn2+-Fur (50 nM) protected 30 nucleotides of the coding strand and 24 nucleotides of the noncoding strand of the fecIR promoter. Higher amounts of Mn2+-Fur (100 nM) covered 41 nucleotides of the coding strand of the fecIR promoter and 38 nucleotides of the coding strand of the fecA promoter. The corresponding region of the noncoding strand of the fecA promoter was hypersensitive to DNase I. The results of a deletion analysis of the fecA promoter supported the previously assigned -35 and -10 regions and nucleotide position +11 for FecI-RNA polymerase interaction. Induction of fecIR transcription by iron limitation increased fecB-lacZ transcription 3.5-fold, whereas under constitutive fecIR transcription, iron limitation increased fecB-lacZ transcription twofold. The two iron-regulated sites of fec transport gene transcription suggest a fast response to sufficient intracellular iron concentrations by repression of fecABCDE transcription and a slower adaptation as the result of fecIR transcription inhibition.
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PMID:Iron regulates transcription of the Escherichia coli ferric citrate transport genes directly and through the transcription initiation proteins. 957 33