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Journal of Bacteriology, August 1999, p. 4639-4643, Vol. 181, No. 15
0021-9193/99/$04.00+0

OxyR and SoxRS Regulation of fur

Ming Zheng,1 Bernard Doan,1 Thomas D. Schneider,2 and Gisela Storz1,*

Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892,1 and Laboratory of Experimental and Computational Biology, National Cancer Institute, Frederick, Maryland 217022

Received 9 April 1999/Accepted 21 May 1999

The cytotoxic effects of reactive oxygen species are largely mediated by iron. Hydrogen peroxide reacts with iron to form the extremely reactive and damaging hydroxyl radical via the Fenton reaction. Superoxide anion accelerates this reaction because the dismutation of superoxide leads to increased levels of hydrogen peroxide and because superoxide elevates the intracellular concentration of iron by attacking iron-sulfur proteins. We found that regulators of the Escherichia coli responses to oxidative stress, OxyR and SoxRS, activate the expression of Fur, the global repressor of ferric ion uptake. A transcript encoding Fur was induced by hydrogen peroxide in a wild-type strain but not in a Delta oxyR strain, and DNase I footprinting assays showed that OxyR binds to the fur promoter. In cells treated with the superoxide-generating compound paraquat, we observed the induction of a longer transcript encompassing both fur and its immediate upstream gene fldA, which encodes a flavodoxin. This polycistronic mRNA is induced by paraquat in a wild-type strain but not in a Delta soxRS strain, and SoxS was shown to bind to the fldA promoter. These results demonstrate that iron metabolism is coordinately regulated with the oxidative stress defenses.

* Corresponding author. Mailing address: NIH, Building 18T, Room 101, 18 Library Dr., MSC 5430, Bethesda, MD 20892-5430., Phone: (301) 402-0968. Fax: (301) 402-0078. E-mail: storz{at}helix.nih.gov.

Journal of Bacteriology, August 1999, p. 4639-4643, Vol. 181, No. 15
0021-9193/99/$04.00+0


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