Transcriptional regulation of the sodA gene, a member of the soxRS regulon encoding the manganese-containing superoxide dismutase (MnSOD; superoxide:superoxide oxidoreductase, EC 18.104.22.168) of Escherichia coli, was examined in a variety of regulatory mutants. Diamide, an oxidant that causes the anaerobic biosynthesis of the MnSOD polypeptide and also facilitates insertion of manganese at the active site, was found to anaerobically induce MnSOD in both soxRS and fur arcA fnr strains. Metal chelating agents also caused anaerobic induction of MnSOD in a fur arcA fnr triple mutant; however, this induction of MnSOD and of glucose-6-phosphate dehydrogenase (G6PD) by 1,10-phenanthroline was dependent on an intact soxRS locus. A strain of E. coli bearing a fusion of the soxS promoter to lacZ was used to demonstrate that both diamide and 1,10-phenanthroline caused anaerobic activation of soxS transcription. These results indicate that (i) both diamide and 1,10-phenanthroline induce the soxRS regulon anaerobically by stimulation of soxS transcription; (ii) diamide, but not metal chelators, also induces MnSOD biosynthesis by a soxRS-independent mechanism, perhaps mediated by effects on fur, arcA, or fnr-mediated repression of sodA; and (iii) the soxRS locus contains a metal-binding component and is responsive to the redox status of the cell
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