A rule-based model for ERBB receptor signaling. Boxes and nested boxes represent proteins and (sub)components of proteins. Only (sub)components considered in the model are shown. Boxes are decorated with post-translational modification flags, which are each labeled at one end and connected to a small box at the other. The prefix of the label indicates the modification (i.e., ‘p’ represents addition of a phosphate group), and the rest of the label indicates the site of modification. Compartmental locations of proteins are indicated in tabs at the lower left corners of boxes: M, membrane; C, cytoplasmic; Ex, extracellular; and En, endosomal. A line that begins and ends with an arrowhead represents a direct binding interaction. A line with a circle at one end identifies an enzyme-substrate relationship; the circle identifies the substrate. A line that ends with an open, triangular arrowhead represents activation. Numbers next to arrows refer to sets of rules, which are identified in an accompanying model guide. See Methods for additional details.