  Are "turn-on" and "turn-off" functions in protein-protein interaction
networks exact opposites of each other? To answer this question, we implement a
minimal model for the evolution of functional protein-interaction networks
using a sequence-based mutational algorithm, and apply the model to study
neutral drift in networks that yield oscillatory dynamics. We study the roles
of activators and deactivators, two core components of oscillatory protein
interaction networks, and find a striking asymmetry in the roles of activating
and deactivating proteins, where activating proteins tend to be synergistic and
deactivating proteins tend to be competitive.
