Regulation of Iron Sequestration Systems in Escherichia Coli and Salmonella Typhimurium (Heme, Outer Membrane)
Regulation of iron uptake systems by iron, growth temperature, and heme was examined. Operon fusions were constructed in which the lactose utilization genes were fused to the promoter of the iron-regulated gene which encodes the colicin I receptor. Regulation by iron was shown to be at the level of transcription. A regulatory mutant was isolated from a cir-lac operon fusion strain which was aberrant in response to iron. When grown in high iron medium, (beta)-galactosidase activity was eight times higher in this mutant then in the parental strain. The mutation, which I call cirR, was linked to cirA, the receptor structural gene, at approximately 45 minutes on the E. coli chromosome. A CirA('+) CirR('-) strain bound four-fold greater amounts of ('125)I-colicin Ia when grown in high iron medium than the parental strain (CirA('+) CirR('+)). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of outer membrane proteins isolated from a cirR strain revealed an increase in the level of the 74K protein which functions as the colicin I receptor. The levels of other outer membrane proteins normally regulated by iron were not affected. CirR was found to be a cis dominant mutation.
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign