Identification of an essential domain in the herpesvirus VP1/2 tegument protein: The carboxy terminus directs incorporation into capsid assemblons

The herpesvirus tegument is a layer of viral and cellular proteins located between the capsid and envelope of the virion. The VP1/2 tegument protein is critical for the propagation of all herpesviruses examined. Using an infectious clone of the alphaherpesvirus pseudorabies virus, we have made a collection of truncation and in-frame deletion mutations within the VP1/2 gene (UL36) and examined the resulting viruses for spread between cells. We found that the majority of ihe VP1/2 protein either was essential for virus propagation or did not tolerate large deletions. A recently described amino-terminal deubiquitinase-encoding domain was dispensable for alphaherpesvirus propagation, but the rate of propagation in an epithelial cell line and the frequency of transport in axons of primary sensory neurons were both reduced. We mapped one essential domain to a conserved sequence at the VP1/2 carboxy terminus and demonstrated that this domain sufficient to redirect the green fluorescent protein to capsid assemblons in nuclei of infected cells.