Team:Calgary/Lab/Signalling

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• Signalling Circuit
• Reporter Circuit
• Mutant Circuits
• Response Circuit

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Figure 1. AI-2 signalling cascade in the absence (left) and presence (right) of AI-2.

In the absence of AI-2, LuxQ autophosphorylates and subsequently phosphorylates the cytoplasmic protein LuxU, which passes its phosphate to LuxO. Phospho-LuxO complexes with transcription factor σ54 to activate the transcription of genes downstream of one of the five qrr4 promoters. The promoter depicted here is qrr4, as it is the one engineered into our system. (b) In the presence of AI-2, LuxQ changes from a kinase to a phosphatase, and thus removes the phosphate of LuxU, which subsequently removes the phosphate of LuxO. Nothing binds to the qrr4 promoter and therefore there is no expression of downstream genes.
Figure 2. Schematic depiction of AI-2 signalling circuit.

This genetic circuit encodes the proteins necessary for the AI-2 signalling cascade (see Figure 1). Curved arrows represent promoters, while straight arrows represent genes. The luxOU operon is under constitutive control of the TetR promoter (BBa_R0040), whereas the ∆luxPQ operon is under control of the ∆σ70 promoter, allowing for control of expression levels. For simplicity, the terminators after each operon are not shown in this circuit.


For an in depth look at the construction of the signalling circuit complete with results, please see the papers below or at the following links: LuxPQ & LuxOU. These papers both deal with signalling circuit construction, although from different perspectives: LuxPQ and LuxOU.
Signalling Circuit LuxPQ

Signalling Circuit LuxOU