Figure 1

Cartoon and mathematical representation of the ancestral pathway, used in the evolutionary simulations, and its dynamical response to two ligand molecules. The latter is obtained by solving the set of differential equations describing the concentration of each protein in the pathway and is used in the calculation of pathway fitness. Gray areas indicate the time brackets when pathway response through effector 1 $E_1^A$ and $E_1^B$) and effector 2 ($E_2^A$ and $E_2^B$) are evaluated (see Methods). Proteins labeled as two and three correspond to a receptor and "global deactivator" (i.e. non-specific phosphotase) respectively. Interaction coefficients are shown as a matrix, listing the actions of other proteins on a given protein row-by-row.