Figure 5.

The activity range of the input promoters affects the function of the AND gate circuit. In top panel, the experimental fluorescence of the B9 and F11 gates is shown as a function of I₁ and I₂. In the bottom panel, the theoretical transfer function (bottom) is calculated using equation (1) and the fit values for the parameters a and b. The white boxes show the ranges for the wild type as well as the F11 and B9 mutants, which have progressively weaker rbss. These boxes are drawn on the basis of range of the one-dimensional transfer functions (Figure 3). It is only the B9 clone that behaves like an AND gate, requiring the maximal activation of both promoters before the output is turned on. In contrast, the F11 clone always shows some activity at high levels of I₂, independent of I₁.