FIG. 7.

Schematic diagram illustrating the proposed mechanism by which portal incorporation is limited to the initiation step of capsid assembly. The model postulates that (i) the scaffolding protein, UL26.5, is found in the form of a head-to-tail polymer and (ii) the portal attaches only at one end of the polymer, as illustrated in step 1, with major capsid protein molecules bound to all other scaffold molecules. Procapsid formation is suggested to occur by successive steps in which one major capsid protein molecule is delivered to a growing edge of the nascent procapsid (steps 2 and 3). Note that the proposed mechanism restricts portal incorporation to the initiation step.