TRANSCRIPTIONAL REGULATION OF MN-SUPEROXIDE DISMUTASE GENE (SODA) OF ESCHERICHIA-COLI IS STIMULATED BY DNA GYRASE INHIBITORS

The expression of manganese-containing superoxide dismutase (sodA) in Escherichia coli using sodA::lacZ gene fusion was found to be stimulated by DNA gyrase inhibitors, nalidixic acid, or coumermycin A1. Aerobically, the gyrase inhibitors increased the expression of sodA::lacZ in the presence or absence of either paraquat or the iron chelator 2,2′-dipyridyl. The concentrations of the inhibitors used were found to reduce DNA supercoiling. Treatment of wild-type cells (sodA+) with nalidixic acid increased the transcription of MnSOD mRNA. Anaerobically, the expression of sodA::lacZ in wild-type cells was not affected by nalidixic acid. However, nalidixic acid had a stimulatory effect on the anaerobic expression of sodA::lacZ in cells preinduced by the iron chelator as well as in mutants derepressed in sodA expression by virtue of their lacking the trans-acting represser proteins or the cis-acting regulatory elements needed for sodA regulation. The results indicate that the effect of DNA gyrase inhibitors is secondary to the cis-and trans-regulatory elements of sodA and suggest that changes in DNA topology may affect transcriptional regulation of sodA. © 1992.