Open AccessMechanism for iron-regulated transcription of the Escherichia coli cir gene: metal-dependent binding of fur protein to the promoters
Author(s) -
David W. Griggs,
J Konisky
Publication year - 1989
Publication title -
journal of bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.652
H-Index - 246
eISSN - 1067-8832
pISSN - 0021-9193
DOI - 10.1128/jb.171.2.1048-1054.1989
Subject(s) - promoter , biology , operon , repressor , gene , transcription (linguistics) , rna polymerase , microbiology and biotechnology , genetics , binding site , dna footprinting , footprinting , dna , aerobactin , transcription factor , gene expression , rna , escherichia coli , enterobacteriaceae , linguistics , philosophy
The molecular basis for the greatly elevated expression of the cir gene (encoding the colicin I receptor) in cells unable to maintain a critical supply of intracellular iron was investigated by genetic and biochemical means. Deletion analysis of the cloned promoter region allowed delineation of sequences necessary for control of transcription initiating at the two promoters, P1 and P2. Gel retardation assays were used to demonstrate both binding of purified Fur (ferric uptake regulation) protein to the iron control region and lack of binding to DNA fragments which are not involved in cir regulation. An operator sequence spanning 43 to 47 base pairs and completely encompassing the two promoters was identified by DNase I protection experiments (footprinting), with binding occurring in a metal-dependent fashion. Thus, during iron-replete growth, Fur appears to act as a repressor of transcription by blocking formation of a DNA-RNA polymerase complex, analogous to the mechanism previously described for regulation of the aerobactin operon (V. de Lorenzo, S. Wee, M. Herrero, and J.B. Neilands, J. Bacteriol. 169:2624-2630, 1987). Characterized and putative Fur recognition sites from several genes were analyzed and classified by statistical methods.