A synthetic genetic circuit whose signal-response curve is temperature-tunable from band-detection to sigmoidal behaviour

Programming new cellular functions by using synthetic gene circuits is a key goal in synthetic biology, and an important element of this process is the ability to couple to the information processing systems of the host cell using synthetic systems with various signal-response characteristics. Here, we present a synthetic gene system in Escherichia coli whose signal-response curve may be tuned from band detection (strongest response within a band of input concentrations) to a switch-like sigmoidal response, simply by altering the temperature. This change from a band-detection response to a sigmoidal response has not previously been implemented. The system allows investigation of a range of signal-response behaviours with minimal effort: a single system, once inserted into the cells, provides a range of response curves without any genetic alterations or replacement with other systems. By altering its output, the system may couple to other synthetic or natural genetic circuits, and thus serve as a useful modular component. A mathematical model has also been developed which captures the essential qualitative behaviours of the circuit.