Assembly protein. PRD1 virions are composed of a tail-less icosahedral capsid of diameter 63 nm, an inner protein-lipid membrane, and a dsDNA genome which is located inside the lipid vesicle. The DNA is packaged into a preformed procapsid. The internal membrane plays an active role in DNA delivery to the host cell by forming a tubular structure used for injecting the DNA into the host cytoplasm.