Mechanism for iron-regulated transcription of the Escherichia coli cir gene: metal-dependent binding of fur protein to the promoters

Abstract

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. 169:2624Bacteriol. 169: -2630Bacteriol. 169: , 1987. Characterized and putative Fur recognition sites from several genes were analyzed and classified by statistical methods.

Identification of iron-activated and -repressed Fur-dependent genes by transcriptome analysis ofNeisseria meningitidisgroup B

“…A 21-bp Neisseria consensus that shares Ϸ80% homology to the E. coli consensus has been derived and proposed to be the binding sequence of the Neisseria Fur protein (23). Although the 19-and 21-bp consensuses serve as good indicators to identify a Furregulated gene, the Fur-binding sequence identified in the promoters of several Fur-regulated genes differed from the classical Fur-binding sequence (37)(38)(39)(40)(41)(42). In light of these results, the Fur-binding sequence has been reinterpreted to be a combination of three repeats of 6-bp 5Ј-NAT(A͞T)AT-3Ј rather than a 19-bp palindrome (24).…”

Evidence of an Unusually Long Operator for the Fur Repressor in the Aerobactin Promoter of Escherichia coli

“…The promoter of the operon responsible for the biosynthesis of the aerobactin siderophore (referred hereafter as Paer) is particularly interesting in this respect (26,32,33,34). Unlike other promoters controlled by Fur in which the operator involves a clear-cut target sequence (13,24,(27)(28)(29), Paer is bound by the repressor to three distinct extents depending on the concentration of the protein ( Fig. 1 and see below).…”

Characterization of secA-sod operon in Borrellia burgdorferi.

“…With concentrations of 1, 10, and 25 mM of Desferal, no reduction of growth was observed ( Figure 9A). This observed lack of effect was unusual since other bacteria like E. coli cease to grow in complex media in the presence of 100 µM Desferal (Griggs and Konisky, 1989). Similarly, no inhibition of growth was observed with dipyridyl at concentrations of 0.1 to 1 mM ( Figure 9B).…”

“…The highest mRNA expression was observed in stationary phase cells; therefore, metalloregulation of secA-sod message was investigated in B. burgdorferi cells grown to stationary phase. Obviously, Fe was the first candidate to be tested because of the well-documented Fur regulation of sod genes (Griggs and Konisky, 1989;Neiderhoffer et al, 1990;Stojiljkovic et al, 1994;Zheng et al, 1999).…”

“…Iron uptake is regulated in Gram-negative bacteria by the repressor protein Fur (Bsat and Helmann, 1999;Griggs and Konisky, 1989;Stojiljkovic et al, 1994;Zheng et al, 1999 (Frechon and Cam, 1994;Ochsner et al, 1995). Analysis of such regions yielded a Fur-binding consensus sequence or "Fur box," which consisted of a 19-bp palindromic sequence, GATAATGATAATCATTATC.…”