ISOLATION AND IN-VITRO PHOSPHORYLATION OF SENSORY TRANSDUCTION COMPONENTS CONTROLLING ANAEROBIC INDUCTION OF LIGHT-HARVESTING AND REACTION-CENTER GENE-EXPRESSION IN RHODOBACTER-CAPSULATUS

Anaerobic induction of light harvesting and reaction center gene expre ssion involves two transacting factors termed RegA and RegB. Sequence and mutational analysis has indicated that RegA and RegB constitute co gnate components of a prokaryotic sensory transduction cascade with Re gB comprising a membrane-spanning sensor kinase and RegA a cytosolic r esponse regulator. In this study we have purified RegA, as well as a t runcated portion of RegB (RegB') and undertaken an in vitro analysis o f autophosphorylation and phosphotransfer activities. Incubation of Re gB' with [gamma-P-32]ATP and MgCl2 resulted in phosphorylation of RegB ' (RegB'similar to P) over a 20-min incubation period. Incubation of R egB'similar to P with RegA resulted in rapid transfer of the phosphate from RegB' to RegA. In analogy to other characterized prokaryotic sen sory transduction components, mutational and chemical stability studie s also indicate that RegB' is autophosphorylated at a conserved histid ine and that RegA accepts the phosphate from RegB at a conserved aspar tate.