INTRA-NUCLEAR LOCALIZATION OF 2 ENVELOPE PROTEINS, GB AND GD, OF HERPES-SIMPLEX VIRUS

The envelopes of herpes simplex virus (HSV) particles are acquired fro m the inner nuclear membrane (INM) of the infected cell and virus-code d glycoproteins are present in the envelope of mature virions. Our ult rastructural study examined the process of virus envelopment and the t argeting of two major viral glycoproteins, gB and go, to the INM in HS V-infected human embryonic fibroblasts. It was shown that envelopment and transport of virus particles from the nucleus is facilitated by th e formation of a dynamic tubulo-reticulum arising from the INM. Capsid s were assembled in the nucleus and collected within INM tubules which protruded into the perinuclear space and thence into the cisternae of the endoplasmic reticulum (ER). Envelopment occurred by constriction and fusion of the tubular channel walls, releasing enveloped virions i nto the ER. Transport to the cell surface took place in membrane-bound compartments and probably followed the normal secretory pathway throu gh the Golgi apparatus. Immunogold probes, tagged with specific monocl onal antibodies, were used to localize gB and go during the process of virus maturation. Cytoplasmic membranes were not labelled, but probes bound inside the nucleus, mainly at sites of virus assembly. Labellin g occurred on the nucleoplasmic side of the INM which surrounded capsi ds in the process of envelopment, but not on the outside of that membr ane, although characteristic gB glycoprotein spikes were labelled on t he envelopes of extracellular virus particles and on virions in trans- Golgi transport vesicles just prior to their release from the infected cell. gB was not detected on the surface of enveloped virions in the perinuclear space, or the cisternae of the ER or cis-Golgi, which sugg ests that the specific epitope was masked during that stage of intrace llular processing. go probes bound to virion envelopes and also to the tegument region of some particles found in both perinuclear and extra cellular sites. We postulate that precursor core proteins for both gB and go are transported first to the nucleus, and then, together with m aturing capsids, are targeted to the INM, and later inserted into vira l envelopes at the site of budding. Post-translational glycosylation o f envelope proteins could occur as virus particles exit the nucleus an d travel through the ER and Golgi compartments.