OxyR: a regulator of antioxidant genes.

The study of the bacterial response to hydrogen peroxide has given general insights into how cells defend against deleterious oxidants. Treatment of Salmonella typhimurium and Escherichia coli cells with low doses of hydrogen peroxide results in the induction of 30 proteins and resistance to killing by higher doses of hydrogen peroxide. The expression of nine of the hydrogen peroxide-inducible proteins, including the antioxidant enzymes catalase, glutathione reductase and an alkyl hydroperoxide reductase, is controlled by the positive regulator oxyR. Strains carrying deletions of the oxyR gene are hypersensitive to hydrogen peroxide and have increased levels of spontaneous mutagenesis during aerobic growth. The OxyR protein is homologous to the LysR-NodD family of bacterial regulatory proteins and binds to the promoters of oxyR-regulated genes. The oxidized, but not the reduced, form of the OxyR protein activates transcription of oxyR-regulated genes in vitro, suggesting that direct oxidation of the OxyR protein brings about a conformation change by which OxyR senses an oxidative stress signal and then activates the expression of defense activities.