Figure 1.

Abstract ternary protein complex. (A) The protein B in this abstract complex acts as a communication pathway between the two other proteins A and C. Binding protein A sends information over the pathway λ to the binding site of protein C, facilitating the binding of protein C. (B) Like a communication channel, the ternary complex can be described by a number of conditional probabilities. The conditional probabilities P(C = 0|A = 0) and P(C = 1|A = 1), describe the accuracy of the communication channel, i.e. the likelihood that a given output signal corresponds to the appropriate input signal. A second set of probabilities, P(C = 1|A = 0) and P(C = 0|A = 1), describes the intrinsic noise of the communication channel, i.e. the likelihood that a given input signal is not correctly conveyed.