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Intracellular forms of pseudorabies virus parental DNA were examined before and after the onset of viral DNA synthesis. Before initiation of synthesis, parental viral DNA acquires single-stranded ends. Circular and concatemeric molecules are also observed, indicating that the single-stranded ends are complementary. Viral DNA replication is initiated at an internal site within the DNA molecule, giving rise to characteristic replicative loops with single-stranded regions in the trans position. Such replicative loops were seen in unit-size (and smaller than unit-size) linear molecules as well as in circular and concatemeric molecules. These results show that the parental viral DNA molecules that acquire single-stranded ends, and consequently are able to form circles and concatemers, proceed to replicate.

During the first round of the replication of pseudorabies virus DNA, replicating DNA is mainly in the form of circles. The main origin of replication is located inthe region of the molecule bearing the inverted repeat. Replication proceeds unidirectionally from the origin.

The envelope of pseudorabies virions can be removed by treatment with Triton X-100, leaving the nucleocapsid intact. The viral envelope removed in this fashion contains all the glycoproteins and about 40 per cent of the proteins of the virions. Analysis by polyacrylamide gel electrophoresis revealed that the envelope proteins migrate as four distinct peaks, all of which contain glycoproteins. The proteins of the nucleocapsids migrate in the gels as six distinct peaks.