IN-VIVO KINETICS OF A REDOX-REGULATED TRANSCRIPTIONAL SWITCH

SoxR is a transcription activator governing a cellular response to sup eroxide and nitric oxide in Escherichia coil, SoxR protein is a homodi mer, and each monomer has a redox-active [2Fe-2S] cluster. Oxidation a nd reduction off the [2Fe-2S] clusters can reversibly activate and ina ctivate SoxR transcriptional activity, Here, we use electron paramagne tic resonance spectroscopy to follow the redox-switching process of So xR protein ill 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 age nts 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 par alleled the increase and decrease of transcription of soxS, the target gene for SoxR. The kinetic analysis also revealed that an oxidative s tress-linked decrease in soxS mRNA stability contributes to the rapid attainment of a new steady state after SoxR activation, Such a redox s tress-related change ire soxS mRNA stability may represent a new level of biological control.