Abstract
Following infection of BHK-21 cells with Herpes simplex virus type 1 (HSV-1), progeny nucleocapsids in the nucleus acquire a glycoprotein-rich envelope by budding through host-cell nuclear membranes. To investigate the nature of the glycoprotein products assembled in the virion at the nuclear envelope, infected cells were pulse-labeled with [3H]-mannose, an oligosaccharidal core sugar, or [3H]-fucose, a terminal sugar. After various chase periods, the incorporation of these sugars was monitored by electron microscope radioautography. The results show that HSV glycoproteins accumulate very rapidly in nuclear membranes, where they exist only as core-glycosylated precursors, i.e., containing [3H]-mannose but not [3H]-fucose. [3H]-fucose grains are seen mainly over Golgi membranes and over virions located in the Golgi and in other cytoplasmic vesicular structures. Our data support a model where addition of terminal sugars (e.g., fucose) to HSV-1 glycoprotein precursors can occur at the surface of newly enveloped viral particles as the virions themselves egress from the cell via the Golgi apparatus.