Fig. 2
The Discovery and Verification of the Promoter-Slope Parabola Principle. a The performance of cadR biosensors with different constitutive promoters to initiate the expression of cadR. b The relationship between log values of the expression efficiency of cadR promoters (note that the x-axis represents the measured values but not the predicted values, y-axis represents the slope of fitting curve in the panel A) and the slopes of the detection curves. c The procedures and (d) results of the bottom-up pooled screening method for the selection of cadR promoters. e The top-down method based on the Parabola Principle for the discovery of optimum cadR promoters for highly efficient metal detection circuits