Fur positive regulation of iron superoxide dismutase in Escherichia coli: functional analysis of the sodB promoter

• Published in: Journal of bacteriology 2000-07, Vol.182 (13), p.3802-3808
• Main Authors: Dubrac, S, Touati, D
• Format: Article
• Language: English
• Subjects: 2,2'-Dipyridyl - pharmacology; Aerobiosis; Anaerobiosis; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacteriology; Base Sequence; Cell division; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Escherichia coli; Escherichia coli - drug effects; Escherichia coli - enzymology; Escherichia coli - genetics; Fur protein; Gene Expression Regulation, Bacterial - drug effects; Gene Expression Regulation, Enzymologic - drug effects; Genetics and Molecular Biology; Integration Host Factors; Iron - metabolism; Iron Chelating Agents - pharmacology; Life Sciences; Molecular Sequence Data; Promoter Regions, Genetic; Recombinant Fusion Proteins - genetics; Regulatory Sequences, Nucleic Acid; Repressor Proteins - genetics; Repressor Proteins - metabolism; Ribonucleic acid; RNA; RNA Stability; RNA, Bacterial; RNA, Messenger; sodB gene; Superoxide Dismutase - genetics; Trans-Activators - genetics; Trans-Activators - metabolism; Transcriptional Activation
• ISSN: 0021-9193; 1098-5530
• DOI: 10.1128/JB.182.13.3802-3808.2000

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.