FIG. 7.
Schematic of lsr and lsrRK operon regulation. cAMP-CRP and LsrR are involved in transcriptional control of lsr and lsrRK operons. cAMP-CRP, a positive regulator, stimulates expression of both operons in the absence of glucose, while LsrR prevents their expression. The function of LsrR is inhibited when cell density increases and inducer phospho-AI-2 accumulates. In addition, cAMP-CRP stimulates transcription from the lsrK promoter, and σs negatively regulates lsr expression (50). Also included in the schematic is the yneE gene, whose expression is increased by luxS. Gray boxes denote promoter. Plus and minus signs indicate positive and negative transcriptional regulation. DPD, 4,5-dihydroxy-2,3-pentanedione.