Escherichia coli proteins inducible by oxidative stress mediated by the superoxide radical.

Two-dimensional gel analyses were made of proteins synthesized in Escherichia coli during various O2- -generating conditions. Nine proteins were constitutively synthesized over wild-type levels in superoxide dismutase (sodA sodB) double mutants. Addition of redox cycling agents such as paraquat and plumbagin at various concentrations induced up to 13 proteins in wild-type cells. Among these 13 were 5 of the 9 constitutively synthesized in the sodA sodB double mutants. Addition of these agents to the superoxide dismutase mutants in low micromolar concentrations induced an additional set of 14 proteins. The proteins induced included only five proteins that have been previously associated with stress responses, consisting of endonuclease IV (Nfo), three oxyR-regulated proteins, and one heat shock protein. O2- -mediated induction of the superoxide inducible (Soi) proteins in the wild type was independent of the oxyR+ gene for all but the three oxyR-regulated proteins. Analyses of proteins from three soi::lacZ gene fusions previously isolated (T. Kogoma, S. B. Farr, K. M. Joyce, and D. O. Natvig, Proc. Natl. Acad. Sci. USA 85:4799-4803, 1988) indicated the specific loss of one of these induced proteins in each fusion strain and the constitutive expression of some Soi proteins.