Isolation of the Escherichia coli iron superoxide dismutase gene: evidence that intracellular superoxide concentration does not regulate oxygen-dependent synthesis of the manganese superoxide dismutase.

A mixed-sequence synthetic oligodeoxynucleotide probe was used to identify clones within the Escherichia coli genomic library of Clarke and Carbon having an extrachromosomal copy of iron superoxide dismutase. Plasmids pLC13-47 and pLC18-11 were shown to contain the structural gene of the iron superoxide dismutase and to overproduce this protein under conditions of chloramphenicol amplification of plasmid copy number. The activities of both manganese and iron proteins were measured in extracts of host cells and plasmid-bearing cells grown over a wide range of oxygenation. The results confirm previous demonstrations that the manganese protein is repressed under anaerobic conditions and induced in the presence of oxygen. Induction of the manganese protein with increasing oxygenation was quantitatively similar in cells differing approximately equal to 7-fold in iron superoxide dismutase, suggesting that the intracellular concentration of superoxide might not be responsible for regulating synthesis of the manganese-containing superoxide dismutase.