Preprocessing of an input signal by a repressor reduces sensitivity of output to low input intensity signals. (a) Equilibrium concentration of processed signal, S′, in relation to original signal input intensity, S, obtained by solution of Eq. (5). The four curves from bottom to top show decreasing levels of signal titration by the repressor for the parameter values α=0.01,0.1,0.5,1000. The top curve alters the initial signal very little, so that S′≈S, showing the consequences of an unfiltered input signal. (b) The processed input signal, S′, is used as the input to a standard Michaelis-Menten reaction kinetics process in Eq. (1), leading to an equilibrium output, A∗. The curves from bottom to top derive from the corresponding preprocessed input signal from the upper panel.