Study of redox-regulated transcription factors in prokaryotes

Several prokaryotic regulatory proteins that respond to changes in oxygen tension or the presence of oxidative agents have now been identified. The Fnr protein governs the expression of numerous genes during anaerobic growth, both as a transcriptional activator and as a repressor. OxyR protein responds to cellular exposure to H2O2 to stimulate transcription of several defense proteins. SoxR protein is triggered by superoxide or nitric oxide to activate a multigene regulon for antioxidant defense and antibiotic resistance. Each of these proteins has been purified and characterized for DNA binding and transcriptional activity in vitro. Fnr, OxyR, and SoxR all seem to respond directly to redox signals generated in the cell, and their in vitro properties support this view: Fnr has an oxygen-sensitive [4Fe-4S] center essential for DNA binding; OxyR may be activated via oxidation of a key cysteine residue; and SoxR activation depends on redox-sensitive [2Fe-2S] centers. Basic methods for genetic and biochemical analysis in these systems are presented, with emphasis on detailed methods for SoxR that illustrate general approaches for all the systems.