Regulation of the FecI-type ECF sigma factor by transmembrane signalling.
Induction of the ferric citrate transport genes of Escherichia coli K-12 involves a signalling cascade that starts at the cell surface and proceeds to the cytoplasm. Three specific proteins are involved: FecA in the outer membrane, FecR in the cytoplasmic membrane, and FecI in the cytoplasm. The binding of dinuclear ferric citrate to FecA causes substantial structural changes in FecA, triggering the signal cascade. The amino-proximal end of FecA interacts with the carboxy-proximal end of FecR in the periplasm. FecR then transmits the signal across the cytoplasmic membrane into the cytoplasm and activates the FecI sigma factor, which binds to the RNA polymerase core enzyme and directs the RNA polymerase to the promoter upstream of the fecABCDE transport genes to initiate transcription. Transcription of the fecIR regulatory genes and the fec transport genes is repressed by the Fur protein loaded with Fe(2+). Therefore, transcription of the fec transport genes is subjected to double control: cells first detect iron deficiency and respond by synthesis of the regulatory proteins FecI and FecR, which initiate transcription of the fec transport genes, provided ferric citrate is available. FecI belongs to the extracytoplasmic function sigma factors, which are widespread among bacteria. With the recent sequencing of complete microbial genomes, it has become apparent that the FecIRA cascade is now a paradigm for the regulatory control of FecI family sigmas in Gram-negative bacteria.
Mikrobiologie/Membranphysiologie, Universtat Tuebingen, Auf der Morgenstelle 28, 72076 Tuebingen, Germany. volkmar.braun@mikrobio.uni-tuebingen.de
Volkmar
V
Braun
Susanne
S
Mahren
Monica
M
Ogierman
D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000502:physiology; D029968:Escherichia coli Proteins; D005290:Ferric Compounds / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D006090:Gram-Negative Bacteria / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D008957:Models, Genetic; D010802:Phylogeny; D016415:Sequence Alignment; D012808:Sigma Factor / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014158:Transcription, Genetic
D029968:Escherichia coli Proteins; C490539:FecI protein, E coli; D005290:Ferric Compounds; D012808:Sigma Factor; C025314:ferric citrate