Premium
Transcriptional regulation of ferric citrate transport in Escherichia coli K‐12. Fecl belongs to a new subfamily of σ 70 ‐type factors that respond to extracytoplasmic stimuli
Author(s) -
Angerer Annemarie,
Enz Sabine,
Ochs Martina,
Braun Volkmar
Publication year - 1995
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.1995.mmi_18010163.x
Subject(s) - biology , escherichia coli , transcription (linguistics) , promoter , rna polymerase , microbiology and biotechnology , transcription factor , biochemistry , subfamily , binding site , dna , gene , gene expression , philosophy , linguistics
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 Fecl, and Fecl activates transcription of the fecABCDE transport genes. In this communication, Fecl was isolated after cloning fecl downstream of an ideal ribosome‐binding site. Overexpressed Fecl formed inclusion bodies which were solubilized and purified in active form using a mild detergent. Fecl, in conjunction with RNA polymerase core enzyme, directed transcription from the fecA promoter in an in vitro run‐off transcription assay. Furthermore, Fecl 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 Fecl‐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, Fecl and FecR. These data support the previous assignment of Fecl, based on sequence homologies, to a new subfamily of eubacterial RNA polymerase σ 70 factors that respond to extra‐cytoplasmic stimuli and regulate extracytoplasmic functions.