 Although the "luxS" gene, which encodes the protein responsible for AI-2 production is widespread, the latter has mainly a primary metabolic role in the recycling of S-adenosyl-L-methionine, with AI-2 being a by-product of that process.An unequivocally AI-2 related behavior was found to be restricted primarily to organisms bearing known AI-2 receptor genes.Thus, while it is certainly true that some bacteria respond to AI-2, it is doubtful that it is always being produced for purposes of signaling.