Replication of herpesvirus DNA. VI. Virions containing either isomer of pseudorabies virus DNA are infectious

Pseudorabies virus DNA exists in two isomeric forms in which the short unique sequence is present in two orientations with respect to the long unique sequence. The viral DNA present in the virions of 21 individual plaques was analyzed. In all cases, equimolar amounts of the two isomeric forms of the DNA were present, indicating that isomerization of the DNA is a rapid process which is complete by the time a small plaque (<2 mm) has developed. Virions containing either isomeric form of the DNA adsorb equally well to cells and either isomeric form of the DNA has the same likelihood of becoming associated with the cell nucleus and to form circles (or concatemers) before initiation of DNA synthesis. The two isomeric forms of viral DNA are also equally represented in the genomes that mature first from concatemeric replicating DNA in cells infected at low multiplicities (0.01 PFU/cell). Furthermore, during the first round of DNA replication in cells infected at low multiplicity, equimolar amounts of the two isomeric forms of the DNA replicate. Since, in this experiment, each cell was infected with a maximum of one viral particle per cell, we conclude that virions containing either isomeric form of the DNA can initiate infection. Previous data (J. M. DeMarchi, T. Ben-Porat, and A. S. Kaplan, 1979, Virology97,457–463) have indicated that each cell, in which infection is initiated, is able to produce a plaque. We therefore conclude that virions containing either isomeric form of the DNA are infectious.