Transcriptional regulation of ferric citrate transport in Escherichia coli K‐12. Fecl belongs to a new subfamily of σ⁷⁰‐type factors that respond to extracytoplasmic stimuli

Abstract

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.

Metabolic Context and Possible Physiological Themes of ς54-Dependent Genes inEscherichia coli

“…FecI and 28 (FliA) are required for synthesis of the ferric citrate transporter and flagella, respectively (8,115). As mentioned above, 54 is usually associated with nitrogen assimilation.…”

Two Extracytoplasmic Function Sigma Subunits, ς E and ς FecI , of Escherichia coli : Promoter Selectivity and Intracellular Levels

“…The holoenzyme E E is responsible for transcription of at least 10 genes (32), of which 4 have been identified, including rpoH, which encodes H for transcription of the heat shock response genes (9,31); degP, which encodes a periplasmic protease for degradation of misfolded proteins (14,23,31,34); fkpA, which encodes a periplasmic peptidylprolyl isomerase (4); and rpoE itself (31). On the other hand, the fecI gene was originally identified as a regulatory gene for the ferric dicitrate transport system (30), but after sequencing, the FecI protein was recognized as a member of the extracytoplasmic function (ECF) subfamily of factor (hereafter referred to as FecI in this report) (1,24). Transcription of the ferric dicitrate transport system of E. coli is repressed by Fe 2ϩ -Fur and activated by ferric dicitrate (2,7,12).…”

Signal transduction pathway of TonB-dependent transporters

“…The signaling domain relays transporter occupancy to the regulatory protein FecR in the cytoplasmic membrane (4,5), which then releases the factor FecI into the cytoplasm (4,(6)(7)(8). FecI promotes binding of RNA polymerase to the promoter upstream of the ferric citrate import operon, thereby initiating transcription (9,10). Although transport and signaling are ferric citrate-and TonB-dependent processes, these functions are ultimately separable because removing the signaling domain abolishes ferric citrate-mediated transcriptional activation, whereas ferric citrate import remains unaffected (11,12).…”