Protease I is involved in virion assembly and maturation. Protease I cleaves the portal protein to yield mature procapsids competent for DNA packaging (Probable). Isoform scaffold protein Z probably helps the capsid proteins to assemble into a functional capsid (Probable). Might interact with viral portal protein; this interaction gives rise to an early 25S initiator complex (Probable). The scaffolding protein Z and the capsid protein T should then be added to the initiator complex to yield immature prohead (Probable). Host GroEL and GroES are also essential for the correct assembly of viral head. Expressed in the late phase of the viral replicative cycle. Expression of late genes is activated by the viral late transcription activator C. The N-terminus is acetylated. Belongs to the peptidase U35 family.