In silico genetic regulatory network. The network consists of a cascade, a pair of mutually repressive genes, an auto-activation and sequestration motif, and an agonist-induced receptor down-regulation motif. (A) When ligand is absent, genes A, E, C, and H are in a “HIGH” state, indicating maximal levels of their respective transcripts and proteins, whereas genes D, G, K, and J are in a “LOW” state, indicating minimal levels of their respective transcripts and proteins. In this state transcripts and protein for gene F are absent. (B) When ligand is present, genes F, D, G, K, and J are in the HIGH state while genes A, C, E, and H are in a LOW state. Signed solid arrows indicate transcriptional regulatory interactions; dashed arrows indicate protein-protein interactions.