The seven-iron FdI from Azotobacter vinelandii regulates the expression of NADPH: ferredoxin reductase via an oxidative stress response
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- Yannone, S. & Burgess, B. JBIC (1998) 3: 253. doi:10.1007/s007750050229
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Previous studies have established that disruption of the fdxA gene that encodes Azotobacter vinelandii ferredoxin I (AvFdI) leads to overexpression of NADPH: ferredoxin reductase (FPR). Investigation of the mechanism of this regulatory system has shown that, in response to fdxA disruption, FPR levels are increased because of transcriptional activation in a manner dependent upon a specific DNA sequence. That sequence is similar to the defined SoxS binding site of Escherichia coli. Using A. vinelandii fpr-luciferase fusion reporter constructs here we show that, like E. coli SoxRS-regulated genes, the A. vinelandii fpr gene is activated by the superoxide propagator paraquat and that the response occurs via the same DNA sequence that is responsive to fdxA disruption. Using a ΔsoxR strain of E. coli and the same reporter constructs we show that, when introduced into E. coli, the A. vinelandii fpr promoter is controlled by SoxRS. Although the two systems are functionally similar and must have structural similarities at the level of DNA-binding specificity for the SoxS-like recognition sequence, data are presented to show that they are likely to have differences at the protein/gene level. The results suggest that in A. vinelandii the specific function of FdI is to serve as the redox sensor that inactivates the paraquat-responsive system and that other organisms (e.g. Pseudomonas, Caulobacter) that have homologous ferredoxins might have similar regulatory systems.