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-51 is modified by geranylation, which is essential for activity (PubMed:12067344, PubMed:17617699). Modified by the tryptophan prenyltransferase ComQ before export to the extracellular environment (By similarity). 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.