EXPRESSION AND REGULATION OF THE SODF GENE ENCODING IRON-CONTAINING AND ZINC-CONTAINING SUPEROXIDE-DISMUTASE IN STREPTOMYCES-COELICOLOR MULLER

Streptomyces coelicolor Muller contains two superoxide dismutases (SOD s), nickel-containing (NiSOD) and iron- and zinc-containing SOD (FeZnS OD), The sodF gene encoding FeZnSOD was isolated by using PCR primers corresponding to the N-terminal peptide sequence of the purified FeZnS OD and a C-terminal region conserved among known FeSODs and MnSODs. Th e deduced amino acid sequence exhibited highest similarity to Mn- and FeSODs from Propionibacterium shermanii and Mycobacterium spp. The tra nscription start site of the sodF gene was determined by primer extens ion. When the sodF gene was cloned in pIJ702 and introduced into Strep tomyces lividans TK24, it produced at least 30 times more FeZnSOD than the control cells. We disrupted the sodF gene in S. lividans TK24 and found that the disruptant did not produce any FeZnSOD enzyme activity but produced more NiSOD. The expression of the cloned sodF gene in TK 24 cells was repressed significantly by Ni, consistent with the regula tion pattern in nonoverproducing cells. This finding suggests that the cloned sodF gene contains the cis-acting elements necessary for Ni re gulation. When the sodF mRNA in S. coelicolor Muller cells was analyze d by S1 mapping of both 5' and 3' ends, we found that Ni caused a redu ction in the level of monocistronic sodF transcripts. Ni did not affec t the stability of sodF mRNA indicating that it regulates transcriptio n. S. lividans TK24 cells overproducing FeZnSOD became more resistant to oxidants such as menadione and lawsone than the control cells, sugg esting the protective role of FeZnSOD, However, the sodF disruptant su rvived as well as the wild-type strain in the presence of these oxidan ts, suggesting the complementing role of NiSOD increased in the disrup tant.