Fig. 1.

Specification of Reaction Rules. Binding of two molecules. One has four binding and modification sites, but only one of them y1173 affects interaction: it must be unbound and phosphorylated. Another has two binding sites, both must be unbound, but the site Y773 must be unphosphorylated. Sites in grey (also have a question mark) do not affect interaction and may be bound to other molecules, or be in different states. Dashed lines with a question mark specify that such sites may be either bound to their respective binding partners or remain unbound, with no effect on the reaction Thus this reaction rule specifies an individual reaction for each state of Y1068 site of EGFR molecule, and possibly many more if EGFR can be bound to other molecules. The result of interaction is formation of a bond (marked with 1) between two sites