REDOX SIGNAL-TRANSDUCTION - MUTATIONS SHIFTING [2FE-2S] CENTERS OF THE SOXR SENSOR-REGULATOR TO THE OXIDIZED FORM

SoxR is a [2Fe-2S] transcription factor triggered by oxidative stress and activated in vitro by one-electron oxidation or assembly of the ir on-sulfur centers. To distinguish which mechanism operates in cells, w e studied constitutively active SoxR (SoxR(c)) proteins. Three SoxR(c) proteins contained [2Fe-2S] centers required for in vitro transcripti on and, like wild-type SoxR, were inactivated by chemical reduction. H owever, in vivo spectroscopy showed that even without oxidative stress , the three SoxR(c) proteins failed to accumulate with reduced [2Fe-2S ] (less than or equal to 4% compared to greater than or equal to 40% f or wild type). One SoxR(c) protein had a redox potential 65 mV lower t han wild type, consistent with its accumulation in the oxidized (activ ated) form in vivo. These results link in vitro and in vivo approaches showing novel redox regulation that couples an iron-sulfur oxidation state to promoter activation.