EXTRACELLULAR SIGNAL PROTEIN TRIGGERING THE PROTEOLYTIC ACTIVATION OF A DEVELOPMENTAL TRANSCRIPTION FACTOR IN BACILLUS-SUBTILIS

We present biochemical evidence for an intercellular signal transduction pathway in B. subtilis. This pathway governs the conversion of the proprotein pro-sigma(E) to the mature transcription factor rho(E). Proteolytic processing is mediated by the membrane protein SpoIIGA and is triggered by the inferred extracellular signal protein SpoIIR. A factor in conditioned medium from B. subtilis cells engineered to produce SpoIIR during growth triggered processing in protoplasts of B. subtilis cells that had been engineered to produce SpoIIGA and pro-sigma(E). The factor was also detected in, and partially purified from, extracts of SpoIIR-producing cells of E. coli. We speculate that SpoIIGA is both a receptor and a protease and that SpoIIR interacts with SpoIIGA on the outside of the cytoplasmic membrane, activating the intracellular protease domain of SpoIIGA.