Part of a major quorum-sensing system that regulates the development of genetic competence (PubMed:12067344). Acts through the activation of the two-component regulatory system ComP/ComA composed of a sensor histidine kinase, ComP, and a response regulator, ComA (By similarity). Interacts directly with the sensor histidine kinase ComP and stimulates its activity. Trp-56 is modified by geranylation, which is essential for activity (PubMed:12067344, PubMed:16407988, PubMed:22197102). Modified by the tryptophan prenyltransferase ComQ before export to the extracellular environment (PubMed:22197102). The type of isoprenyl derivative differs among the different pherotypes and depends on ComX primary sequence (PubMed:12067344, PubMed:14679219). 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. In ComX, the sole conserved residue is the modified tryptophan essential for the activity.