Abstract
Despite differences in the pathogenesis and host range of alphaherpesviruses, many stages of their morphogenesis are thought to be conserved. Here, an ultrastructural study of bovine herpesvirus 1 (BoHV-1) envelopment revealed similar profiles to those previously found for HSV-1, with BoHV-1 capsids associating with endocytic tubules. Consistent with the similarity of their genomes and envelopment strategies, the proteomic composition of BoHV-1 and HSV-1 virions was also comparable. However, BoHV-1 morphogenesis exhibited a diversity in envelopment events. First, heterogeneous primary envelopment profiles were readily detectable at the inner nuclear membrane of BoHV-1 infected cells. Second, the BoHV-1 progeny comprised not just full virions, but also an abundance of capsidless, non-infectious light (L)-particles that were released from the infected cell in similar numbers to virions, and in the absence of DNA replication. Proteomic analysis of BoHV-1 L- particles and the much less abundant HSV-1 L-particles revealed that they contained the same complement of envelope proteins as virions but showed variations in tegument content. In the case of HSV-1, the UL46 tegument protein was reproducibly found to be more than 6-fold enriched in HSV-1 L-particles. More strikingly, the tegument proteins UL36, UL37, UL21 and UL16 were depleted in BoHV-1 but not HSV-1 L-particles. We propose that these combined differences reflect the presence of a truly segregated “inner” and “outer” tegument in BoHV-1, making it a critical system for studying the structure and process of tegumentation and envelopment.