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Review
. 1999 Oct;181(20):6223-9.
doi: 10.1128/JB.181.20.6223-6229.1999.

Opening the iron box: transcriptional metalloregulation by the Fur protein

L Escolar  1 , J Pérez-Martín, V de Lorenzo
Affiliations
Review

Opening the iron box: transcriptional metalloregulation by the Fur protein

L Escolar et al. J Bacteriol. 1999 Oct.
No abstract available

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Figures

FIG. 1
FIG. 1
Regulation of iron transport in E. coli. This classical model of response to iron starvation still remains basically correct (4). It is based on the existence of two configurations of the Fur protein in an equilibrium which is displaced by Fe2+ towards the form competent for binding DNA and thus for repression of transcription. The lack of iron results in the derepression of an entire collection of genes for the biosynthesis and transport of siderophores and hence the activity of one or more high-affinity iron uptake systems. These scavenge the Fe3+ present in the medium and drive ferrisiderophore complexes through an elaborate transport scheme which includes not only specific outer membrane receptors but also periplasmic and inner membrane proteins. The metal is then reduced intracellularly to Fe2+. Transport of this chemical element in aerobically grown cells is subjected to a very fine tuning, since iron overload promotes generation of the highly reactive forms of oxygen.
FIG. 2
FIG. 2
Alternative interpretations of the Fur box. The scheme shows different views of the 19-bp sequence bound by the repressor and generally known as the Fur box or the iron box in E. coli. The standard interpretation considers this box as a palindromic sequence composed of two 9-bp inverted repeats. However, it is also possible to conceive the same sequence as an array of three repeats of 6 bp (two directed and one inverted) of the invariable sequence NATA/TAT (22). Fur binding sites can then be assembled by combining multiple repeats in various orientations (see the text for explanation).
FIG. 3
FIG. 3
Rules that govern the generation of Fur binding sites. Active targets for the Fur-Fe2+ complex can be assembled by combining a minimum of three repeats of NATA/TAT. (A) The thymines present in the core sequence AT-AT of each repeat are directly engaged in interactions with the repressor (22). The presence of a central T residue in the upper or the lower strand probably determines the orientation of each minimal unit in the array. (B) The combination in any orientation of three repeats (i.e., three units of 6 bp each) gives rise to a functional Fur box. Those found in natural promoters generally adopt the configuration two direct/one inverted repeat. (C) The grouping of a Fur box with a number of adjacent hexamers with various degrees of similarity to NATA/TAT originate secondary sites (such as sites II found in a number of promoters). In come cases, extended protections caused by the polymerization of the protein can be observed along neighboring DNA segments with less sequence similarity.
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References

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