Sensor in the two-component regulatory system ComP/ComA involved in a major quorum response pathway that regulates the development of genetic competence. Plays a role in sporulation, at least partly interchangeable with that of SpoIIJ. Probably activates ComA by phosphorylation. ATP + protein L-histidine = ADP + protein N-phospho-L-histidine. Autophosphorylates on a histidine and transfers the phosphate group onto an aspartate in ComA, thus activating it. The DNA sequences encoding comQ, comX and the N-terminal two-thirds of comP show a striking polymorphism, which determines the specificity of the quorum-sensing system in the different pherotypes of Bacillus.