Identification of cis site involved in nickel-responsive transcriptional repression of sodF gene coding for Fe- and Zn-containing superoxide dismutase of Streptomyces griseus.

A sodF gene coding for iron- and zinc-containing superoxide dismutase (FeZnSOD) of Streptomyces griseus was cloned and sequenced. A 5' end of 0.8-kb sodF transcript was mapped at the 57 nucleotides upstream from an ATG initiation codon. Employing expressions of sodF::xylE fusions in trans in Streptomyces lividans, nickel-responsive transcriptional repression was found to be relieved if mutations were introduced into an operator sequence of inverted-repeat, TTGCAN(7)TGCAA, which traverses the 5' end (+1, G) of the sodF mRNA. Nickel-dependent interaction between cell extracts and sodF regulatory DNA, monitored through gel-mobility shift assay, was abolished when the operator was mutated. Recombinant sodF operon having operator mutations showed protein level and enzyme activity, which were no longer repressed by nickel, suggesting that nickel-responsive repression of FeZnSOD is regulated mainly at the level of transcription through the operator.