Molecular mechanisms of primary and secondary envelopment in herpesvirus morphogenesis

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Virion formation and egress of herpesviruses involve two separate budding steps which are differentiated by the subcellular compartments in which they occur and the proteins involved. Primary envelopment of intranuclear genome-containing nucleocapsids at the inner nuclear membrane is followed by fusion of the primary envelope with the outer nuclear membrane resulting in release of nucleocapsids into the cytoplasm. Secondary (and final) envelopment then occurs after addition of the tegument by budding of intracytoplasmic nucleocapsids into vesicles in the trans- Golgi network. Although several of the viral proteins involved have been identified and functionally characterized, the molecular interactions that govern both processes are still largely unclear. We will focus on two areas: (i) identification of virally encoded components of the primary envelope and tegument, and elucidation of interaction between them and intranuclear nucleocapsids, and between viral and cellular nuclear proteins to clarify the molecular basis for primary envelopment; and (ii) interaction between virally encoded components of the secondary envelope and tegument with cytoplasmic nucleocapsids to gain more insight into the basis of secondary envelopment. In addition, the requirements for transport of vesicles containing enveloped virions to the cell surface followed by release of mature herpes virions will be investigated.