Fig. 4.

Hybrid promoters are tunable. a Diagram of the hybrid promoters showing essential features. Each promoter contained a proximal operator site for either AraC or LasR, the −10 and −35 sites from the library shown in Fig. 2, the constant reporter sequence, and two operator sites for the transcriptional repressor LacI. b Transcription rate of the AraC- and LacI-regulated hybrid promoters as a function of the relative equilibrium constant of σ-factor binding to the −10 and −35 sites for four different conditions: neither inducer (black), only arabinose (gray), only IPTG (red), and both arabinose and IPTG (blue). The thermodynamic model (solid curves) was fit to the results of each combination of the −10 and −35 sites. c Same as b, but for the LasR- and LacI-regulated hybrid promoters and with 3OH-C12-HSL instead of arabinose. Experiments were performed with biological triplicates. Error bars have been omitted for clarity as they are, in most cases, smaller than the size of the symbols. Thermodynamic modeling data and experimental data are available in Supplementary Information and Supplementary Data 5