Exponentially growing cells are more sensitive to oxidants such as hydrogen peroxide and superoxides than stationary phase cells. Using disruption mutations in the genes encoding the two superoxide dismutases, we show that the principal mechanism of toxicity of redox-cycling compounds, such as menadione and plumbagin, is via the production of superoxide anions. Using two-dimensional polyacrylamide gel electrophoresis we have compared the pattern of protein expression in cells labelled with -[S]methionine and stressed with either HO or menadione. Three groups of proteins were evident: those whose levels are elevated by both HO and menadione, and those specifically induced by either HO or menadione. Experiments with promoter fusions demonstrated that one of the heat inducible forms of HSP70 () was inducible with HO. Furthermore, induction of the yeast HO-responsive promoter by menadione required the metabolism of menadione.


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