Scaffolding protein involved in the icosahedric procapsid assembly. Coassembles with the capsid proteins to form the procapsid, in which the scaffolding protein is found within the external shell of icosahedrally arranged capsid protein subunits. In a subsequent step the scaffolding protein molecules are released from the procapsid. Facilitates assembly by binding to gp10 hexamers but not the pentamers and locking them into a morphogenically correct conformation. Belongs to the T7likevirus capsid assembly scaffolding protein family.