Herpes simplex virus tegument protein VP16 is a component of primary enveloped virions

Immunogold electron microscopy was used to determine whether the tegument proteins VP13/14, VP22, and VP16 of herpes simplex virus type 1 (HSV1) are components of primary enveloped virions. Whereas VP13/14 and VP22 were not detected in virus particles in the perinuclear space and were present in only mature extracellular virions, VP16 was acquired prior to primary envelopment of the virus at the inner nuclear membrane. This finding highlights potential similarities and differences between HSV1 and the related alphaherpesvirus, pseudorabies virus, in which the homologues of all three of these tegument proteins are not incorporated into the virion until secondary envelopment.