Rule-based model of early signaling events mediated by the epidermal growth factor receptor (EGFR). (a) Global view of the model with an Extended Contact Map (ECM) (see  for more detailed explanation of the notation), which shows protein components - catalytic domains and sites of binding and postranslational modification - and their interactions. (b) Translation of one interaction (shown in red) from the ECM into a reaction rule in a rule-based model. The rule indicates that a specific tyrosine residue on EGFR (Y1048) must be phosphorylated in order for GRB2 to bind through its SH2 domain. The absence of other components in the rule indicates that the rate of binding is not affected by the status of other components of either protein - in other words, this rule neglects cooperative or allosteric effects.