Mutational analysis and membrane topology of ComP, a quorum-sensing histidine kinase of Bacillus subtilis controlling competence development

ComP is a sensor histidine kinase of Bacillus subtilis required for the sig nal transduction pathway that initiates the development of competence for g enetic transformation. It is believed that ComP senses the presence of ComX , a modified extracellular peptide pheromone, and donates a phosphate to Co mA, thereby activating this transcription factor for binding to the srfA pr omoter. In the present study, fusions to the Escherichia coli proteins PhoA and LacZ and analysis of its susceptibility to the protease kallikrein wer e used to probe the membrane topology of ComP. These data suggest that ComP contains six or eight membrane-spanning segments and two large extracytopl asmic loops in its N-terminal membrane-associated domain. Deletions were in troduced involving the large extracellular loops to explore the role of the N-terminal domain of ComP in signal transduction. The absence of the secon d loop conferred a phenotype in which ComP was active in the absence of Com X. The implications of these data are discussed.