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Metalloregulation in vitro of the aerobactin promoter of Escherichia coli by the Fur (ferric uptake regulation) protein
Author(s) -
Escolar Lucía,
Lorenzo Víctor de,
PérezMartíín José
Publication year - 1997
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.1997.6211987.x
Subject(s) - aerobactin , biology , rna polymerase , repressor , operon , transcription (linguistics) , promoter , escherichia coli , microbiology and biotechnology , polymerase , dna , rna , binding site , gene , biochemistry , transcription factor , gene expression , enterobacteriaceae , linguistics , philosophy
The mechanism of transcriptional repression of the aerobactin operon of Escherichia coli by the Fe 2+ ‐responsive Fur (ferric uptake regulation) protein has been investigated. In the presence of a divalent metal, such as Mn 2+ , the Fur protein sequentially occupies two defined sites at the aerobactin promoter region, followed by a looser occupation of upstream DNA sequences. However, binding to the primary target site suffices for the entire repression effect. Comparison of transcription patterns generated with run‐off experiments in the presence and absence of heparin showed that access of the RNA polymerase to the principal −35/−10 hexamers of the promoter region was fully prevented by Fur‐Mn 2+ bound to its primary site. Similarly, promoter‐bound RNA polymerase could not be competed out from the DNA even in the presence of a large Fur‐Mn 2+ excess, although the repressor could immediately bind its target sequence at the region as soon as RNA polymerase moved away from the promoter during transcription. The high affinities of either protein for the promoter produce, in practice, a first‐come, first‐served effect that helps the system to respond instantly to changes in the iron status of the cells.