Fig. 1.

The V. harveyi quorum-sensing circuit. At high cell density, the three two-component sensors, CqsS, LuxN and LuxPQ, bind their respective AIs and act as phosphatases, resulting, via LuxU, in dephosphorylation of LuxO. This terminates qrr1–5 sRNA production and permits the translation of the master regulator, LuxR. Quorum-sensing target genes are classified according to their affinity for LuxR as indicated by arrow thicknesses. Class III genes have high affinity for LuxR, Class II genes have intermediate affinity and Class I genes have the lowest affinity. Dashed lines indicate the flow of phosphate at high cell density. The three AIs are CAI-1, HAI-1 and AI-2, and they are synthesized by CqsA, LuxM and LuxS respectively. Hfq is a sRNA chaperone.