 Without glucose, cAMP-CRP is needed to stimulate the "lsr" expression, while LsrR represses its expression in the absence of the inducer, phospho-AI-2.As AI-2 accumulates, more AI-2 is taken in via LsrABCD, phosphorylated via LsrK, and the "lsr" transcription is de-repressed, enabling even more AI-2 uptake.Doubts have been expressed regarding AI-2's status as a universal signal.