RegB/RegA, a global redox-responding two-component system.

The RegB-RegA regulon from Rhodobacter capsulatus and Rhodobacter sphaeroides encodes proteins involved in numerous energy-generating and energy-utilizing processes such as photosynthesis, carbon fixation, nitrogen fixation, hydrogen utilization, aerobic and anaerobic respiration, denitrification, electron transport and aerotaxis. The redox signal that is detected by the membrane-bound sensor kinase, RegB, has been identified to be the ubiquinone pool in the membrane. Regulation of RegB autophosphorylation also involves a redox-active cysteine that is present in the cytosolic region of RegB. Both phosphorylated and unphosphorylated forms of the cognate response regulator RegA are capable of activating or repressing a variety of genes in the regulon. Highly conserved homologues of RegB and RegA have been found in a wide number of photosynthetic and nonphotosynthetic bacteria with evidence suggesting that RegB/RegA have a fundamental role in the transcription of redox-regulated genes in many bacterial species.