Sakacin A is a bacteriocin produced by Lactobacillus sakei Lb706. The gene cluster (sap) encompasses a regulatory unit composed of three consecutive genes, orf4 and sapKR. sapKR encode a histidine protein kinase and a response regulator, while orf4 encodes the putative precursor of a 23-amino-acid cationic peptide (termed Sap-Ph). The authors show that Sap-Ph serves as a pheromone regulating bacteriocin production. Lb706 produced bacteriocin when the growth temperature was kept at 25 or 30 degrees C, but production was reduced or absent at higher temperatures (33.5-35 degrees C). Production was restored by lowering the growth temperature to 30 degrees C, but at temperatures of 33-34 degrees C also by adding exogenous Sap-Ph to the growth medium. A knock-out mutation in orf4 abolished sakacin A production. Exogenously added Sap-Ph complemented this mutation, unambiguously showing the essential role of this peptide for bacteriocin production. Another sakacin A producer, Lactobacillus curvatus LTH1174, had a similar response to temperature and exogenously added Sap-Ph.