Figure 2.

Quorum sensing regulatory circuit in R. leguminosarum bv. viciae. The Cin, Rhi and Rai systems are shown. The Cin system is at the top of the hierarchical regulatory cascade and is required for the activation of the Rhi and Rai systems through the action of the antirepressor CinS. The transcriptional repressor PraR is displaced by CinS at high population densities, allowing activation of the Rhi and Rai systems. ExpR also contributes to the activation of Rhi and Rai by repressing praR transcription. Genes are represented with wide arrows and proteins with rectangles. Green arrows represent activation; red flat-ended lines indicate repression. AHL: N-acyl homoserine lactone.