A human cervical keratinocyte cell line, W12, has been initiated from a low-grade cervical lesion histologically diagnosed as CIN I. This cell line has, to date, undergone over 300 generations in vitro with an average doubling time of 30 hr: an aneuploid karyotype has developed with progressive in vitro growth. W12 contains HPV16 DNA present at approximately 100 copies and the state of the viral DNA over a number of passages has been examined. The HPV16 DNA is stably maintained at high copy number over several passages and restriction enzyme analysis together with electrophoresis of uncleaved viral DNA indicate that it is present predominantly as the episomal molecule. W12 cells exhibit a typical keratinocyte morphology and, when transplanted into the flank of the nude mouse, form an epithelial lesion with the histological features of CIN I/II.

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Infection of eukaryotic cells by enveloped viruses requires fusion between the viral envelope and the cellular plasma or endosomal membrane. The actual merging of the two membranes is mediated by viral envelope glycoproteins, which generally contain a highly hydrophobic region termed the fusion peptide. The entry of herpesviruses is mediated by three conserved proteins: glycoproteins B, H (gH), and L. However, how fusion is executed remains unknown. Herpes simplex virus type 1 gH exhibits features typical of viral fusion glycoproteins, and its ectodomain seems to contain a putative internal fusion peptide. Here, we have identified additional internal segments able to interact with membranes and to induce membrane fusion of large unilamellar vesicles. We have applied the hydrophobicity-atinterface scale proposed by Wimley and White (Wimley, W. C., and White, S. H. (1996) Nat. Struct. Biol. 3, 842-848) to identify six hydrophobic stretches within gH with a tendency to partition into the membrane interface, and four of them were able to induce membrane fusion. Experiments in which equimolar mixtures of gH peptides were used indicated that different fusogenic regions may act in a synergistic way. The functional and structural characterization of these segments suggests that herpes simplex virus type 1 gH possesses several fusogenic internal peptides that could participate in the actual fusion event.

Herpes simplex virus (HSV) nucleocapsids acquire an envelope by budding through the inner nuclear membrane, but it is uncertain whether this envelope is retained during virus maturation and egress or whether mature progeny virions are derived by deenvelopment at the outer nuclear membrane followed by reenvelopment in a cytoplasmic compartment. To resolve this issue, we used immunogold electron microscopy to examine the distribution of glycoprotein D (gD) in cells infected with HSV-1 encoding a wild-type gD or a gD which is retrieved to the endoplasmic reticulum (ER). In cells infected with wild-type HSV-1, extracellular virions and virions in the perinuclear space bound approximately equal amounts of gD antibody. In cells infected with HSV-1 encoding an ER-retrieved gD, the inner and outer nuclear membranes were heavily gold labeled, as were perinuclear enveloped virions. Extracellular virions exhibited very little gold decoration (10-to 30-fold less than perinuclear virions). We conclude that the envelope of perinuclear virions must be lost during maturation and egress and that mature progeny virions must acquire an envelope from a post-ER cytoplasmic compartment. We noted also that gD appears to be excluded from the plasma membrane in cells infected with wild-type virus.Herpesvirus nucleocapsids assemble in the nuclei of infected cells and acquire an envelope by budding through the inner nuclear membrane, but the subsequent route of virus maturation and egress has been a matter of controversy. Over 30 years ago, Stackpole (19) proposed that enveloped virions in the perinuclear space fused with the outer nuclear membrane, releasing into the cytoplasm naked nucleocapsids which acquired a final envelope by budding into a late cytoplasmic compartment. The observation that infectious herpes simplex virions accumulated within cells in the absence of a functional Golgi apparatus (11) implied that virions in the perinuclear space were infectious and suggested that the Golgi apparatus was required merely for egress of these virions. This "single envelopment" pathway, in which perinuclear enveloped virions are transported to the cell surface via the secretory pathway and the envelope glycoproteins are processed in situ, has the virtue of simplicity and became widely accepted as the route of egress of herpes simplex virus (HSV) (e.g., see reference 17). Studies of other alphaherpesviruses, notably varicella-zoster virus and pseudorabies virus, have, however, supported the view that the final envelope is acquired in a cytoplasmic compartment, thus favoring the "two-step envelopment" route of egress (6,8,12,13,22,24). Indeed, several observations are inconsistent with the view that HSV acquires its final envelope from the nuclear membrane: the phospholipid composition of secreted virions is different from that of the nuclear membrane (21); naked nucleocapsids, not enveloped virions, are observed in axons during virus egress (10, 15, 16); and a major tegument component, VP22, is observed apparently exclusively in the cytop...

A glycoprotein encoded by the ULl gene of herpes simplex virus type 1 (HSV-1) was detected in infected cells with antipeptide sera. The ULl gene has previously been implicated in virus-induced cell fusion (S. Little and P. A. Schaffer, Virology 112:686-697, 1981). Two protein species, a 30-kDa precursor form and a 40-kDa mature form of the glycoprotein, both of which were modified with N-linked oligosaccharides, were observed. This novel glycoprotein is the 10th HSV-1 glycoprotein to be described and was named glycoprotein L (gL). A complex was formed between gL and gH, a glycoprotein known to be essential for entry of HSV-1 into cells and for virus-induced cell fusion. Previously, it had been reported that gH expressed in the absence of other viral proteins was antigenically abnormal, not processed, and not expressed at the cell surface (U. A. Gompels and