SoxR is a transcription activator governing a cellular response to superoxide and nitric oxide in Escherichia coli. SoxR protein is a homodimer, and each monomer has a redox-active [2Fe-2S] cluster. Oxidation and reduction of the [2Fe-2S] clusters can reversibly activate and inactivate SoxR transcriptional activity. Here, we use electron paramagnetic resonance spectroscopy to follow the redox-switching process of SoxR protein in vivo. SoxR [2Fe-2S] clusters were in the fully reduced state during normal aerobic growth, but were completely oxidized after only 2-min aerobic exposure of the cells to superoxide-generating agents such as paraquat. The oxidized SoxR [2Fe-2S] clusters were rapidly re-reduced in vivo once the oxidative stress was removed. The in vivo kinetics of SoxR [2Fe-2S] cluster oxidation and reduction exactly paralleled the increase and decrease of transcription of soxS, the target gene for SoxR. The kinetic analysis also revealed that an oxidative stress-linked decrease in soxS mRNA stability contributes to the rapid attainment of a new steady state after SoxR activation. Such a redox stress-related change in soxS mRNA stability may represent a new level of biological control.
Publication Source (Journal or Book title)
Proceedings of the National Academy of Sciences of the United States of America
Ding, H., & Demple, B. (1997). In vivo kinetics of a redox-regulated transcriptional switch. Proceedings of the National Academy of Sciences of the United States of America, 94 (16), 8445-8449. https://doi.org/10.1073/pnas.94.16.8445