Abstract
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.