Figure 2.

(a) A simplified model of a Cdk4 kinase molecule illustrates how basic BioD icons and action arrows can concisely represent intra- and inter-molecular actions. The Cdk4 molecule includes a kinase site (K) that, when active, phosphorylates a phosphorylation site (P) on the RB protein. The kinase site on Cdk4 is activated (filled arrow) by occupancy of its phosphorylation site and inhibited (open-squared arrow) by occupancy of the binding site (dotted circle) that binds the Cdk4 inhibitor p15. (b) An 'event model' derived from the model above. Events are defined as changes of state of one or more functional properties of icons in a state model. Here, for instance, the event model displays a chain of events triggered by an increase of p15 concentration (see text).