Fur Positive Regulation of Iron Superoxide Dismutase in Escherichia coli: Functional Analysis of the sodB Promoter
AUTOR(ES)
Dubrac, Sarah
FONTE
American Society for Microbiology
RESUMO
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 β-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.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=94553Documentos Relacionados
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