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 (FeZn SOD) of Streptomyces griseus was cloned and sequenced. A 5' end of 0.8-kb s odF transcript was mapped at the 57 nucleotides upstream from an ATG initia tion codon. Employing expressions of sodF::xylE fusions in trans in Strepto myces lividans, nickel-responsive transcriptional repression was found to b e relieved if mutations were introduced into an operator sequence of invert ed-repeat, TTGCAN(7)TGCAA, which traverses the 5' end (+1, G) of the sodF m RNA. Nickel-dependent interaction between cell extracts and sonF regulatory DNA, monitored through gel-mobility shift assay, was abolished when the op erator was mutated. Recombinant sodF operon having operator mutations showe d protein level and enzyme activity, which were no longer repressed by nick el, suggesting that nickel-responsive repression of FeZnSOD is regulated ma inly at the level of transcription through the operator. (C) 2000 Elsevier Science B.V. All rights reserved.