Fur positive regulation of iron superoxide dismutase in Escherichia coli: functional analysis of the sodB promoter.
In Escherichia coli, the expression of sodB, which encodes iron superoxide dismutase, has been suggested to be activated by Fur, the iron-responsive global regulator initially characterized as a transcriptional repressor. We investigated sodB regulation by functional analysis of the sodB promoter using sodB-lac fusions with various truncated and mutated promoters. Several cis- and trans-acting elements involved in sodB regulation have been identified. The beta-galactosidase activity of sodB-lacZ reporter fusions and RNA analysis showed sevenfold iron-dependent, Fur-mediated activation of expression. A region just downstream from -10, including a large palindromic sequence encompassing the +1 position followed by a 14-bp AT-rich motif, is the site of Fur positive regulation, and the integrity of both sequences was required for full Fur-mediated activation. The life span of sodB mRNA was three times longer in a fur(+) strain, indicating that Fur-mediated activation proceeds, at least in part, at the posttranscriptional level. The H-NS and IHF histone-like factors also affected sodB expression. IHF slightly repressed sodB expression independently of Fur regulation. In contrast, H-NS negative regulation operated only in the absence of Fur. Remarkably, psodB behaved like a "pure extended -10" promoter. Deletion of the -35 region did not affect expression, whereas expression was totally abolished by a TG-to-CC mutation in the extended -10 sequence TGcTACCCT.
Dubrac
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Institut Jacques Monod, CNRS-Universités Paris 6 et Paris 7, 75251 Paris Cedex 05, France.
Touati
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D015082:2,2'-Dipyridyl / Q000494:pharmacology; D000332:Aerobiosis; D000693:Anaerobiosis; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D001483:Base Sequence; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D034982:Integration Host Factors; D007501:Iron / Q000378:metabolism; D007502:Iron Chelating Agents / Q000494:pharmacology; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D020871:RNA Stability; D012329:RNA, Bacterial; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins / Q000235:genetics; D012045:Regulatory Sequences, Nucleic Acid; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000235:genetics*; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C031908:H-NS protein, bacteria; D034982:Integration Host Factors; D007502:Iron Chelating Agents; D012329:RNA, Bacterial; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D015534:Trans-Activators; C068477:ferric uptake regulating proteins, bacterial; D015082:2,2'-Dipyridyl; D007501:Iron; C087504:SodB protein, Bacteria; D013482:Superoxide Dismutase