The procapsid shell is made up of major capsid proteins (MCP)-containing capsomeres, with six copies of MCP per hexon and five copies of MCP per penton. One of the 12 pentons in each capsid is composed entirely of portal protein (PORT), the UL104 protein, a self-assembling homododecamer. The PORT penton provides a channel for viral DNA encapsidation. Triplex (TRI) complex TRI1:TRI2 is added to stabilize hexons and pentons, and small capsid protein (SCP )decorates the outer capsid surface, interacting with MCP at hexon tips.
Before the capsid has aquired the genome, it is designated a B capsid. Three capsid forms accumulate in the nucleus of herpesvirus-infected cells: A capsids that lack both scaffold and packaged viral DNA, B capsids that contain scaffold but lack viral DNA, and C capsids, contains viral DNA in place of scaffold and probably represents nucleocapsids in the process of maturation.