Role of Intranuclear Sacs, Intrasaccate Tubes, and Cytoplasmic Dense Bodies in the Structural Completion of Cytomegalovirus

The addition of tegument or matrix proteins and the outermost membrane to human cytomegalovirus (strain AD 169) replicating in human cells appeared to occur differently in the nucleus than in the cytoplasm. In the nucleus cytomegalovirus was completed structurally within intranuclear sacs, as envelopment at the end of tubular structures, containing an electron-dense material, included tegument and outer membrane simultaneously. In the cytoplasm structural completion occurred in separate steps. Tegument could be added by association with dense bodies; then, interaction with the membranes of vacuoles or vesicles provided the outermost covering. Tubes originating in intranuclear sacs have been described previously only in guinea pig cells infected with guinea pig cytomegalovirus.