title: Functional interaction of region 4 of the extracytoplasmic function sigma factor FecI with the cytoplasmic portion of the FecR transmembrane protein of the Escherichia coli ferric citrate transport system.
abstract: Transcriptional regulation of the ferric citrate transport genes of Escherichia coli is initiated by the binding of ferric citrate to the outer membrane protein FecA. This binding elicits a signal that is transmitted by FecR across the cytoplasmic membrane into the cytoplasm, where the sigma factor FecI directs the RNA polymerase to the promoter upstream of the fecABCDE genes. An in vivo deletion analysis using a bacterial two-hybrid system assigned the interaction of the FecR and FecI proteins to the cytoplasmic portion of the FecR transmembrane protein and region 4 of FecI. Missense mutations randomly generated by PCR were localized to region 4 of FecI, and the mutants were impaired with regard to the interaction of FecR with FecI and fecB-lacZ transcription. The cloned region 4 of FecI interfered with fecB-lacZ transcription. Interaction of N-proximal regions of predicted FecR homologs with region 4 of predicted FecI homologs of Pseudomonas aeruginosa was demonstrated. The interaction was specific in that only cognate protein pairs interacted with each other; no interactions occurred between heterologous combinations of the P. aeruginosa proteins and between a P. aeruginosa FecI homolog and E. coli FecR. The results demonstrate that region 4 of FecI specifically binds FecR and that this binding is necessary for FecI to function as a sigma factor.
authors.affiliation: Mikrobiologie/Membranphysiologie, Universität Tübingen, D-72076 Tübingen, Germany.
authors.forename: Susanne
authors.initials: S
authors.lastname: Mahren
authors.forename: Sabine
authors.initials: S
authors.lastname: Enz
authors.forename: Volkmar
authors.initials: V
authors.lastname: Braun
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D005290:Ferric Compounds / Q000378:metabolism*; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D017354:Point Mutation; D017434:Protein Structure, Tertiary; D011550:Pseudomonas aeruginosa / Q000378:metabolism; D017384:Sequence Deletion; D017386:Sequence Homology, Amino Acid; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C490539:FecI protein, E coli; C093541:FecR protein, E coli; D005290:Ferric Compounds; D026901:Membrane Transport Proteins; D012808:Sigma Factor; C025314:ferric citrate