Proteins specified by herpes simplex virus. XIII. Glycosylation of viral polypeptides

Global aspects of viral glycosylation

Enveloped viruses encompass some of the most common human pathogens causing infections of different severity, ranging from no or very few symptoms to lethal disease as seen with the viral hemorrhagic fevers. All enveloped viruses possess an envelope membrane derived from the host cell, modified with often heavily glycosylated virally encoded glycoproteins important for infectivity, viral particle formation and immune evasion. While N-linked glycosylation of viral envelope proteins is well characterized with respect to location, structure and site occupancy, information on mucin-type O-glycosylation of these proteins is less comprehensive. Studies on viral glycosylation are often limited to analysis of recombinant proteins that in most cases are produced in cell lines with a glycosylation capacity different from the capacity of the host cells. The glycosylation pattern of the produced recombinant glycoproteins might therefore be different from the pattern on native viral proteins. In this review, we provide a historical perspective on analysis of viral glycosylation, and summarize known roles of glycans in the biology of enveloped human viruses. In addition, we describe how to overcome the analytical limitations by using a global approach based on mass spectrometry to identify viral O-glycosylation in virus-infected cell lysates using the complex enveloped virus herpes simplex virus type 1 as a model. We underscore that glycans often pay important contributions to overall protein structure, function and immune recognition, and that glycans represent a crucial determinant for vaccine design. High throughput analysis of glycosylation on relevant glycoprotein formulations, as well as data compilation and sharing is therefore important to identify consensus glycosylation patterns for translational applications.

IFI16 restricts HSV-1 replication by accumulating on the hsv-1 genome, repressing HSV-1 gene expression, and directly or indirectly modulating histone modifications

Interferon-γ inducible factor 16 (IFI16) is a multifunctional nuclear protein involved in transcriptional regulation, induction of interferon-β (IFN-β), and activation of the inflammasome response. It interacts with the sugar-phosphate backbone of dsDNA and modulates viral and cellular transcription through largely undetermined mechanisms. IFI16 is a restriction factor for human cytomegalovirus (HCMV) and herpes simplex virus (HSV-1), though the mechanisms of HSV-1 restriction are not yet understood. Here, we show that IFI16 has a profound effect on HSV-1 replication in human foreskin fibroblasts, osteosarcoma cells, and breast epithelial cancer cells. IFI16 knockdown increased HSV-1 yield 6-fold and IFI16 overexpression reduced viral yield by over 5-fold. Importantly, HSV-1 gene expression, including the immediate early proteins, ICP0 and ICP4, the early proteins, ICP8 and TK, and the late proteins gB and Us11, was reduced in the presence of IFI16. Depletion of the inflammasome adaptor protein, ASC, or the IFN-inducing transcription factor, IRF-3, did not affect viral yield. ChIP studies demonstrated the presence of IFI16 bound to HSV-1 promoters in osteosarcoma (U2OS) cells and fibroblasts. Using CRISPR gene editing technology, we generated U2OS cells with permanent deletion of IFI16 protein expression. ChIP analysis of these cells and wild-type (wt) U2OS demonstrated increased association of RNA polymerase II, TATA binding protein (TBP) and Oct1 transcription factors with viral promoters in the absence of IFI16 at different times post infection. Although IFI16 did not alter the total histone occupancy at viral or cellular promoters, its absence promoted markers of active chromatin and decreased those of repressive chromatin with viral and cellular gene promoters. Collectively, these studies for the first time demonstrate that IFI16 prevents association of important transcriptional activators with wt HSV-1 promoters and suggest potential mechanisms of IFI16 restriction of wt HSV-1 replication and a direct or indirect role for IFI16 in histone modification.

Lytic HSV-1 infection induces the multifunctional transcription factor Early Growth Response-1 (EGR-1) in rabbit corneal cells

BACKGROUND

Herpes simplex virus type-1 (HSV-1) infections can cause a number of diseases ranging from simple cold sores to dangerous keratitis and lethal encephalitis. The interaction between virus and host cells, critical for viral replication, is being extensively investigated by many laboratories. In this study, we tested the hypothesis that HSV-1 lytic infection triggers the expression of important multi-functional transcription factor Egr1. The mechanisms of induction are mediated, at least in part, by signaling pathways such as NFκB and CREB.

METHODS

SIRC, VERO, and 293HEK cell lines were infected with HSV-1, and the Egr-1 transcript and protein were detected by RT-PCR and Western blot, respectively. The localization and expression profile of Egr-1 were investigated further by immunofluorescence microscopy analyses. The recruitment of transcription factors to the Egr-1 promoter during infection was studied by chromatin immunoprecipitation (ChIP). Various inhibitors and dominant-negative mutant were used to assess the mechanisms of Egr-1 induction and their effects were addressed by immunofluorescence microscopy.

RESULTS

Western blot analyses showed that Egr-1 was absent in uninfected cells; however, the protein was detected 24-72 hours post treatment, and the response was directly proportional to the titer of the virus used for infection. Using recombinant HSV-1 expressing EGFP, Egr-1 was detected only in the infected cells. ChIP assays demonstrated that NFкB and cAMP response element binding protein (CREB) were recruited to the Egr-1 promoter upon infection. Additional studies showed that inhibitors of NFкB and dominant-negative CREB repressed the Egr-1 induction by HSV-1 infection.

CONCLUSION

Collectively, these results demonstrate that Egr-1 is expressed rapidly upon HSV-1 infection and that this novel induction could be due to the NFкB/CREB-mediated transactivation. Egr-1 induction might play a key role in the viral gene expression, replication, inflammation, and the disease progression.

Varicella zoster virus infection: clinical features, molecular pathogenesis of disease, and latency

Varicella zoster virus (VZV) is an exclusively human neurotropic alphaherpesvirus. Primary infection causes varicella (chickenpox), after which virus becomes latent in cranial nerve ganglia, dorsal root ganglia, and autonomic ganglia along the entire neuraxis. Years later, in association with a decline in cell-mediated immunity in elderly and immunocompromised individuals, VZV reactivates and causes a wide range of neurologic disease. This article discusses the clinical manifestations, treatment, and prevention of VZV infection and reactivation; pathogenesis of VZV infection; and current research focusing on VZV latency, reactivation, and animal models.

High-mobility group protein A1 binds herpes simplex virus gene regulatory sequences and affects their expression

The high-mobility group protein A1 (HMGA1), which regulates mammalian gene expression by altering chromatin architecture, was found to bind at multiple sites within the promoter regions of all of the herpes simplex virus type 1 (HSV-1) immediate early genes, as well as a representative early (tk) gene and one late (gC) gene, both in vitro and in vivo. Infected cell polypeptide (ICP) 4, the major HSV-1 regulatory protein, binds these promoters both in vitro and in vivo, and HMGA1 enhances its in vitro binding. In transient expression experiments, HMGA1 modified the effects of both ICP4 and ICP0, another virus transactivator, on virus gene expression in a promoter-specific manner, but it had no effect on the transactivation of immediate-early promoters by VP16. These data indicate that host-cell architectural chromatin proteins could influence the interactions of host-cell and viral transcription factors with the virus DNA regulatory elements and affect HSV-1 gene expression.

Requirements for the nuclear-cytoplasmic translocation of infected-cell protein 0 of herpes simplex virus 1

Earlier studies have shown that wild-type infected-cell protein 0 (ICP0), a key herpes simplex virus regulatory protein, translocates from the nucleus to the cytoplasm of human embryonic lung (HEL) fibroblasts within several hours after infection (Y. Kawaguchi, R. Bruni, and B. Roizman, J. Virol. 71:1019-1024, 1997). Translocation of ICP0 was also observed in cells infected with the d120 mutant, in which both copies of the gene encoding ICP4, the major regulatory protein, had been deleted (V. Galvan, R. Brandimarti, J. Munger, and B. Roizman, J. Virol. 74:1931-1938, 2000). Furthermore, a mutant (R7914) carrying the D199A substitution in ICP0 does not bind or stabilize cyclin D3 and is retained in the nucleus (C. Van Sant, P. Lopez, S. J. Advani, and B. Roizman, J. Virol. 75:1888-1898, 2001). Studies designed to elucidate the requirements for the translocation of ICP0 between cellular compartments revealed the following. (i) Translocation of ICP0 to the cytoplasm in productive infection maps to the D199 amino acid, inasmuch as wild-type ICP0 delivered in trans to cells infected with an ICP0 null mutant was translocated to the cytoplasm whereas the D199A-substituted mutant ICP0 was not. (ii) Translocation of wild-type ICP0 requires a function expressed late in infection, inasmuch as phosphonoacetate blocked the translocation of ICP0 in wild-type virus-infected cells but not in d120 mutant-infected cells. Moreover, whereas in d120 mutant-infected cells ICP0 was translocated rapidly from the cytoplasm to the nucleus at approximately 5 h after infection, the translocation of ICP0 in wild-type virus-infected cells extended from 5 to at least 9 h after infection. (iii) In wild-type virus-infected cells, the MG132 proteasomal inhibitor blocked the translocation of ICP0 to the cytoplasm early in infection, but when added late in infection, it caused ICP0 to be relocated back to the nucleus from the cytoplasm. (iv) MG132 blocked the translocation of ICP0 in d120 mutant-infected cells early in infection but had no effect on the ICP0 aggregated in vesicle-like structures late in infection. However, in d120 mutant-infected cells treated with MG132 at late times, proteasomes formed a shell-like structure around the aggregated ICP0. These structures were not seen in wild-type virus or R7914 mutant-infected cells. The results indicate the following. (i) In the absence of beta or gamma protein synthesis, ICP0 dynamically associates with proteasomes and is translocated to the cytoplasm. (ii) In cells productively infected beyond alpha gene expression, ICP0 is retained in the nucleus until after the onset of viral DNA synthesis and the synthesis of gamma2 proteins. (iii) Late in infection, ICP0 is actively sequestered in the cytoplasm by a process mediated by proteasomes, inasmuch as interference with proteasomal function causes rapid relocation of ICP0 to the nucleus.

Herpes simplex virus gene expression in neurons: viral DNA synthesis is a critical regulatory event in the branch point between the lytic and latent pathways

Herpes simplex virus establishes a latent infection in peripheral neurons. We examined viral gene expression in rat peripheral neurons in vitro and determined that viral gene expression is attenuated and delayed in these neurons compared with that in Vero cells. In addition, using pharmacologic and genetic blocks to viral DNA synthesis, we found that viral alpha and beta gene expression was upregulated by viral DNA synthesis. Although maximal gene expression in neurons requires viral DNA synthetic activity, activation of viral gene expression was seen even in the presence of herpes simplex virus DNA polymerase inhibitors, but not in the absence of the origin-binding protein. Initiation of viral DNA synthesis is apparently a key regulatory event in the balance between the lytic and latent pathways in peripheral neurons.

The herpes simplex virus UL20 protein compensates for the differential disruption of exocytosis of virions and viral membrane glycoproteins associated with fragmentation of the Golgi apparatus

The Golgi apparatus is fragmented and dispersed in Vero cells but not in human 143TK- cells infected with wild-type herpes simplex virus 1. Moreover, a recombinant virus lacking the gene encoding the membrane protein UL20 (UL20- virus) accumulates in the space between the inner and outer nuclear membranes of Vero cells but is exported and spreads from cell to cell in 143TK- cell cultures. Here we report that in Vero cells infected with UL20- virus, the virion envelope glycoproteins were of the immature type, whereas the viral glycoproteins associated with cell membranes were fully processed up to the addition of sialic acid, a trans-Golgi function. Moreover, the amounts of viral glycoproteins accumulating in the plasma membranes were considerably smaller than those detected on the surface of Vero cells infected with wild-type virus. In contrast, the amounts of viral glycoproteins present on the plasma membranes of 143TK- cells infected with wild-type or UL20- virus were nearly identical. We conclude that (i) in Vero cells infected with UL20- virus the block in the export of virions is at the entry into the exocytic pathway, and a second block in the exocytosis of viral glycoproteins associated with cytoplasmic membranes is due to an impairment of transport beyond Golgi fragments containing trans-Golgi enzymes and not to a failure of the Golgi oligosaccharide-processing functions; (ii) these defects are manifested in cells in which the Golgi apparatus is fragmented; and (iii) the UL20 protein compensates for these defects by enabling transport to and from the fragmented Golgi apparatus.

Herpes simplex virus envelopment and maturation studied by fracture label

Herpes simplex virus envelopment and maturation were investigated by thin-section fracture label. The distribution of glycoproteins B and D was analyzed by labeling with antibodies; the precursor and mature forms of the glycoproteins were differentiated by labeling with the lectins concanavalin A (ConA) and wheat germ agglutinin (WGA), respectively. We report that the two glycoproteins were readily detected in the intracellular virion, whether located between the inner and outer nuclear membranes or within cytoplasmic membrane-bound vesicles and in the inner and outer nuclear membranes themselves. The enveloped virion between the inner and outer nuclear membranes labeled with ConA but not with WGA. During the transit to the extracellular space the reactivity of the virion membranes with ConA decreased and that with WGA ensued. The results document that herpes simplex viruses acquire at the inner nuclear membrane an envelope carrying the immature forms of the glycoproteins and that during the transit to the extracellular space the envelope glycoproteins become of the fully processed type.

Intracellular maturation and sorting of two herpes simplex virus type 1 glycoproteins. Immunogold staining of ultrathin cryosections

Simultaneous immunocytochemical triple staining of ultrathin cryosections of herpes simplex virus type 1-infected cells was carried out using monoclonal antibodies specific for glycoprotein C, glycoprotein D and alpha + beta tubulin. The viral glycoproteins were identified in the cytoplasm, in the Golgi sacs, on the plasma membrane and on the surface of intra- and extracellular virus particles, but not on the nuclear membrane. The glycoproteins identified in the cytoplasm outside the Golgi region were not always confined to the membranes of vesicles, but were often located in close proximity to the tubulin-labelled structures. The glycoproteins C and D were usually codistributed in the cytoplasm, and both accumulated in the Golgi sacs in the same membrane domains. As the glycoproteins occur in close proximity to the microtubular structures, we speculate that these might be directly involved in the intracellular transport of viral glycoproteins.

Origin of unenveloped capsids in the cytoplasm of cells infected with herpes simplex virus 1

In cells infected with herpes simplex viruses the capsids acquire an envelope at the nuclear membrane and are usually found in the cytoplasm in structures bound by membranes. Infected cells also accumulate unenveloped capsids alone or juxtaposed to cytoplasmic membranes. The juxtaposed capsids have been variously interpreted as either undergoing terminal deenvelopment resulting from fusion of the envelope with the membrane of the cytoplasmic vesicles or undergoing sequential envelopment and deenvelopment as capsids transit the cytoplasm into the extracellular space. Recent reports have shown that (i) wild-type virus attaches to but does not penetrate cells expressing glycoprotein D (G. Campadelli-Fiume, M. Arsenakis, F. Farabegoli, and B. Roizman, J. Virol. 62:159-167, 1988) and that (ii) a mutation in glycoprotein D enables the mutant virus to productively infect cells expressing the wild-type glycoprotein (G. Campadelli-Fiume, S. Qi, E. Avitabile, L. Foa-Tomasi, R. Brandimarti, and B. Roizman, J. Virol. 64:6070-6079, 1990). If the unenveloped capsids in the cytoplasm result from fusion of the cytoplasmic membranes with the envelopes of viruses transiting the cytoplasm, cells infected with virus carrying the mutation in glycoprotein D should contain many more unenveloped capsids in the cytoplasm inasmuch as there would be little or no restriction in the fusion of the envelope with cytoplasmic membranes. Comparison of thin sections of baby hamster kidney cells infected with wild-type and mutant viruses indicated that this was the case. Moreover, in contrast to the wild-type parent, the mutant virus was not released efficiently from infected cells. The conclusion that the unenveloped capsids are arrested forms of deenveloped capsids is supported by the observation that the unenveloped capsids were unstable in that they exhibited partially extruded DNA.

Molecular pathogenesis of equine coital exanthema: identification and expression of infected cell polypeptides at the restricted temperature during equine herpesvirus 3 infection

Equine herpesvirus 3 (EHV-3)-infected equine cells display a kinetics of infected cell polypeptide (ICP) synthesis at 34 degrees C that is typical of coordinate cascade gene regulation of herpesviruses. In contrast, when infected cell cultures are incubated at the restricted temperature of 39 degrees C, the shift from early (beta) gene expression to late (gamma) gene expression is perturbed, i.e., there is an accumulation of early (beta) gene products and a decrease in, or absence of, late (gamma) gene products. Some of the affected late (gamma) gene products may be glycoproteins since these ICPs co-migrated with radiolabeled bands from infected cells incubated with [3H] glucosamine, separated by polyacrylamide gel electrophoresis. These findings are consistent with previous findings (Jacob, 1986), indicating that the growth restriction is in a late viral function(s) and possibly involves envelopment of nucleocapsids into infectious virions.

Crossed immunoelectrophoretic analysis of herpes simplex virus type 2 proteins. Characterization of antigen-5

Herpes simplex virus type 2 proteins extracted from infected cells and analysed by crossed immunoelectrophoresis identified a nonglycosylated antigen named Ag-5. The antigen contained two proteins when extracted from the agarose gel and the molecular weights were 128K and 91K. Both proteins are located in the nucleus of the infected cells and the 128K is identical to ICP-8. The 91K protein is based on the reactivity with monoclonal antibodies most likely the alkaline exonuclease mapped by Preston and Cordingly (25). Our data show that although the proteins ICP-8 and 91K coprecipitate they differ in both peptide composition and in immunological specificity.

Processing of N-linked oligosaccharides from precursor- to mature-form herpes simplex virus type 1 glycoprotein gC

Immature and mature forms of glycoprotein gC were purified by immunoadsorbent from herpes simplex virus type 1-infected BHK cells labeled with [3H]mannose for a 20-min pulse or for 11 h followed by a 3-h chase. The nature of N-asparagine-linked oligosaccharides carried by the immature form, pgC (molecular weight = 92,000), and the mature gC (molecular weight = 120,000) has been investigated. All pronase-digested glycopeptides of pgC were susceptible to endo-beta-N-acetylglucosaminidase H treatment; thus they have a high-mannose structure. Using thin-layer chromatography to separate endo-beta-N-acetylglucosaminidase H-cleaved oligosaccharides, polymannosyl chains of different sizes, ranging from Man9GlcNAc to Man5GlcNAc, were separated. The major components were Man8GlcNAc and Man7GlcNAc, suggesting that pgC labeled in a 20-min pulse represents the form of glycoprotein already routed to the Golgi apparatus. Analysis of glycopeptides of mature gC showed that the majority (95%) of N-linked glycans were converted to complex-type glycans. Ion-exchange chromatography and affinity chromatography on concanavalin A-Sepharose and leucoagglutinin-agarose revealed that diantennary and triantennary glycans predominated, whereas tetrantennary chains were not present. Parts of the di- and triantennary chains were not fully sialylated. The high heterogeneity of complex-type chains found in mature gC may be related to the high number of N-glycosylation sites of the glycoprotein as predicted by DNA sequencing studies (Frink et al., J. Virol. 45:634-647, 1983).

Genome locations of temperature-sensitive mutants in glycoprotein gB of herpes simplex virus type 1

A plasmid containing a herpes simplex virus type 1 (HSV-1) insert from strain KOS, prototypic coordinates 0.345 to 0.368 (3.45 kilobases) was mutagenized in vitro, and potential mutations were introduced into intact viral DNA by cotransfection. Functions normally associated with the glycoprotein gB are in the 1-9 complementation group, and the above coordinates include those that specify the gB glycoprotein gene. Following cotransfection, individual plaques were screened for temperature sensitivity (ts) of viral growth. A total of seven ts mutants was obtained, of which four were spurious mutations due to alterations outside the cloned sequences, presumably mediated by some aspect of the Ca-precipitation-cotransfection method. The remaining three did not complement known mutants of the 1-9 complementation group. These three mutants, along with tsJ12 (P.A. Schaffer, G.M. Aron, N. Biswal, and M. Benyesh-Melnick, 1973, Virology 52, 57-71) and tsJ33 (C.-T. Chu, D.S. Parris, R.A.F. Dixon, F.E. Farber, and P.A. Schaffer, 1979, Virology 98, 168-181), were physically located by marker-rescue experiments to three different restriction fragments between 0.345 to 0.368 map units. Sodium dodecyl sulfate-gel electrophoresis was used to analyze the glycoproteins synthesized during continuous or pulse-chase labeling protocols. All five mutants were found to synthesize a precursor of gB but did not accumulate mature gB during a pulse, a chase, or continuous labeling at the nonpermissive temperature.

Interactions of monoclonal antibodies and bovine herpesvirus type 1 (BHV-1) glycoproteins: characterization of their biochemical and immunological properties

Hybridoma cell lines producing monoclonal antibodies to bovine herpes virus type 1 (BHV-1) were established. The monoclonal antibodies were characterized with respect to their antigen specificities and biological activities. One group of eight monoclonal antibodies precipitated the glycoproteins GVP 3 (180K) and GVP 9 (91K), a second group of thirteen monoclonal antibodies precipitated GVP 6 (130K), GVP 11 (74K) and GVP 16 (55K), and one monoclone secreted antibodies specific for GVP 7 (105K). Analysis of the immune precipitates by electrophoresis under nonreducing conditions suggested that GVP 3 is a dimer of GVP 9. It also indicated that GVP 11 and GVP 16 are components of a disulfide-linked complex, GVP 6. The results, obtained by immunoprecipitation were confirmed by Western blot analysis and an enzyme-linked immunosorbent assay (ELISA), using electrophoretically separated viral glycoproteins. In addition, these techniques demonstrated differential reactivities of the monoclonal antibodies with GVP 11 and GVP 16. The monoclonal antibodies were used to analyze the biological roles of these three sets of glycoproteins. Monoclonal antibodies directed against GVP 3/GVP 9 did not neutralize viral infectivity, but most of them mediated complement-dependent lysis of the infected cell. Individual monoclonal antibodies directed against GVP 6/GVP 11/GVP 16 could neutralize virus as well as participate in complement-mediated lysis. The only available monoclone against GVP 7 did not show any biological activity in the above two assays. Thus, GVP 6/GVP 11/GVP 16 may contain the attachment site of the virion.

Virus-specific glycoproteins associated with the nuclear fraction of herpes simplex virus type 1-infected cells

Monospecific antisera to herpes simplex virus type 1 (HSV-1) glycoproteins gB, gC, and gD were used to identify the HSV-1-specific glycoproteins associated with the nuclear fraction as compared with those associated with cytoplasmic fraction, whole-cell lysates, and purified virions. The results indicate that a predominance of HSV glycoprotein precursors pgC(105), pgB(110), and pgD(52) is associated with the nuclear fraction. Treatment of the nuclear fraction with the enzyme endo-beta-N-acetylglucosaminidase H indicated that the lower-molecular-weight glycoproteins are sensitive to this endoglycosidase. These results suggest that in the nuclear fraction of HSV-1-infected cells virus-specific glycoproteins gB, gC, and gD are predominately in the high-mannose precursor form; however, detectable amounts of the fully glycosylated forms of gC and gD were also found.

Detection of antibodies to herpes simplex virus with a continuous cell line expressing cloned glycoprotein D

The gene for glycoprotein D of herpes simplex virus type 1 (HSV-1) was expressed in stable mammalian cell lines. Glycoprotein D produced in these cells has a number of antigenic determinants in common with the native glycoprotein. Cell lines expressing glycoprotein D were used in an enzyme-linked immunosorbent assay to detect human antibodies to glycoprotein D. This strategy should prove useful in determining the extent to which the immune response to HSV-1 is directed toward glycoprotein D.

Glycopeptides of the type-common glycoprotein gD of herpes simplex virus types 1 and 2

We have carried out detailed structural studies of the glycopeptides of glycoprotein gD of herpes simplex virus types 1 and 2. We first examined and compared the number of N-asparagine-linked oligosaccharides present in each glycoprotein. We found that treatment of either pgD-1 or pgD-2 with endo-beta-N-acetylglucosaminidase H (Endo H) generated three polypeptides which migrated more rapidly than pgD on gradient sodium dodecyl sulfate-polyacrylamide gels. Two of the faster-migrating polypeptides were labeled with [(3)H]mannose, suggesting that both pgD-1 and pgD-2 contained three N-asparagine-linked oligosaccharides. Second, we characterized the [(3)H]mannose-labeled tryptic peptides of pgD-1 and pgD-2. We found that both glycoproteins contained three tryptic glycopeptides, termed glycopeptides 1, 2, and 3. Gel filtration studies indicated that the molecular weights of these three peptides were approximately 10,000, 3,900, and 1,800, respectively, for both pgD-1 and pgD-2. Three methods were employed to determine the size of the attached oligosaccharides. First, the [(3)H]mannose-labeled glycopeptides were treated with Endo H, and the released oligosaccharide was chromatographed on Bio-Gel P6. The size of this molecule was estimated to be approximately 1,200 daltons. Second, Endo H treatment of [(35)S]methionine-labeled glycopeptide 2 reduced the molecular size of this peptide from approximately 3,900 to approximately 2,400 daltons. Third, glycopeptide 2 isolated from the gD-like molecule formed in the presence of tunicamycin was approximately 2,200 daltons. From these experiments, the size of each N-asparagine-linked oligosaccharide was estimated to be approximately 1,400 to 1,600 daltons. Our experiments indicated that glycopeptides 2 and 3 each contained one N-asparagine-linked oligosaccharide chain. Although glycopeptide 1 was large enough to accommodate more than one oligosaccharide chain, the experiments with Endo H treatment of the glycoprotein indicated that there were only three N-asparagine-linked oligosaccharides present in pgD-1 and pgD-2. Further studies of the tryptic glycopeptides by reverse-phase high-performance liquid chromatography indicated that all of the glycopeptides were hydrophobic in nature. In the case of glycopeptide 2, we observed that when the carbohydrate was not present, the hydrophobicity of the peptide increased. The properties of the tryptic glycopeptides of pgD-1 were compared with the properties predicted from the deduced amino acid sequence of gD-1. The size and amino acid composition compared favorably for glycopeptides 1 and 2. Glycopeptide 3 appeared to be somewhat smaller than would be predicted from the deduced sequence of gD-1. It appears that all three potential glycosylation sites predicted by the amino acid sequence are utilized in gD-1 and that a similar number of glycosylation sites are present in gD-2.

Requirements for transport of HSV-1 glycoproteins to the cell surface membrane of human fibroblasts and Vero cells

The intracellular transport of the HSV-1 glycoproteins gA/gB, gC and gD has been followed by the indirect immunofluorescence technique (IIF). Infected tissue culture cells were stained with monoclonal antibodies made to the individual glycoproteins and with fluorochrome-coupled wheat germ agglutinin reacting specifically with Golgi apparatus of the cells. Staining of either infected, human fibroblasts or of VERO cells at 9 hours p.i. with antibodies to gA/gB showed a prominent ring-like nuclear fluorescence and distinct staining of the Golgi apparatus in the cells. Antibodies to gC and gD stained mainly the Golgi apparatus and areas close to or at the surface of the cells. By immunocytolysis of HSV-1-infected VERO cells the viral glycoproteins were demonstrable at the surface of cells but growth of infected cells in the presence of either TM or monensin inhibited the expression of most of the viral glycoproteins at the cell surface. Blocking of the glycosylation of the viral glycoproteins with tunicamycin (TM) was followed by accumulation of the core of the glycoproteins gA/gB and gD in granular structures close to the nucleus as seen by immunofluorescence microscopy. Antibodies to gC did also stain granules close to the nucleus but in addition the periphery of the cells were stained. Inhibition of intracellular transport from the Golgi apparatus by the carboxylic ionophore monensin was followed by accumulation of all the HSV-1 glycoproteins in vesicles derived from the Golgi apparatus in both human fibroblasts and VERO cells. Our data thus support the hypothesis that the HSV-1 glycoproteins are processed in the Golgi apparatus before the transport to and incorporation into the cell surface membrane of infected cells and into virion envelopes.

Inhibition of glycosylation of herpes simplex virus glycoproteins: identification of antigenic and immunogenic partially glycosylated glycopeptides on the cell surface membrane

The surface membranes of cells infected with herpes simplex virus type 1 (HSV-1), strain KOS, contain three principal glycoproteins, gC (apparent Mr 129k), gB (apparent Mr 120k), and gD (apparent Mr 58k). Infections carried out in the presence of the glycosylation inhibitor 2-deoxy-D-glucose result in the loss of the mature species with the concurrent appearance of lower-molecular-weight polypeptides which are presumably partially glycosylated forms of the fully processed glycoproteins. Specific immunoprecipitation of radiolabeled cytoplasmic extracts of 2-deoxy-D-glucose-inhibited infections identified partially glycosylated proteins designated DG92, DG88, and DG53, which are antigenically related to the corresponding mature forms gB, gC, and gD. Cell surface radioiodination, in combination with specific immunoprecipitation, revealed that DG88 and DG53 were the principal species transported to the cell surface in 2-deoxy-D-glucose-inhibited infections. DG92 was readily detected in the cytoplasm but not on the plasma membrane. Cells infected with the KOS mutant, syn LD70, did not synthesize glycoprotein gC. In glycosylation-inhibited syn LD70 infections, DG88 was not detected in either the cytoplasm or plasma membrane, demonstrating a genetic relationship between DG88 and gC. Polyclonal and monoclonal antibodies directed against the glycoproteins gC, gB, and gD sensitized infected cells to complement-mediated immune cytolysis. Cells infected in the presence of the inhibitor were sensitized to lysis only by antibody specific for gC and gD. The glycosylation-inhibited cells were insensitive to immunolysis by anti-gB monoclonal antibody. These findings confirm that the glycosylation-deficient forms of gC and gD, but not gB reach the cell surface in the presence of inhibitor and that the inhibitor-induced alterations in glycosylation do not cause a complete loss of antigenicity. Inoculation of mice with syngeneic 3T3 cells infected in the presence or absence of inhibitor-induced cytolytic and neutralizing antibody. A major portion of the cytolytic antibody was directed against gC, but anti-gC antibody appeared to play a minor role in virus neutralization. While the serum induced by the control infected cells contained precipitating antibodies for gC, gB, and gD, the serum derived from mice inoculated with inhibitor-treated infected cells had only weak immunoprecipitating activity against gB. Together, these findings have identified partially glycosylated forms of the major HSV glycoproteins and show that complete glycosylation is not required for transport of some of these partially glycosylated polypeptides to the cell surface. Moreover, complete glycosylation of the glycopeptides is not essential for maintenance of antigenicity or immunogenicity, indicating that at least some determinants recognized by antibodies directed against the mature glycoproteins are not affected by 2-deoxy-D-glucose-induced carbohydrate alterations.

The effect of ammonium chloride and tunicamycin on the glycoprotein content and infectivity of herpes simplex virus type 1

Infectious virions of MP, a syncytial strain of herpes simplex virus type 1, are formed in the presence of 50 mM NH4Cl. Underglycosylated virion glycoproteins are synthesized in infected cells and are incorporated into virions in the presence of the same concentration of NH4Cl. We conclude that fully glycosylated glycoproteins are not required for viral infectivity. Virus particles, deficient in glycosylated glycoproteins, are assembled in the presence of tunicamycin but they are not infectious. The decrease in infectivity could be due to the decreased amount of the gB or possibly other peptides and/or to the lack of the high-mannose saccharides of precursor glycoproteins.

Infectivity and glycoprotein processing of herpes simplex virus type 1 grown in a ricin-resistant cell line deficient in N-acetylglucosaminyl transferase I

We report on the replication of herpes simplex virus type 1 (HSV-1) and viral glycoprotein processing in RicR14 cells, a mutant ricin-resistant cell line defective in N-acetylglucosaminyl transferase I activity. In these cells HSV-1(MP) and (F) replicated to yields very similar to those in parental BHK cells. The kinetics of HSV-1 adsorption in mutant and in parent cells was also essentially identical. Progeny virions from ricin-resistant and wild-type cells displayed comparable specific infectivities. However, in the mutant cells the efficiency of plating of progeny virus from both RicR14 and BHK cells was reduced. HSV-1(MP) failed to induce syncytia in RicR14 cells either in a plaque assay or after a high-multiplicity infection. Moreover, the fully glycosylated forms of glycoproteins (gB, gC, and gD) were totally absent, and only the partially glycosylated precursors (pgC, pgD. and a triplet in the gB-gA region) accumulated in HSV-1-infected ricin-resistant cells and in herpesvirions made in these cells. Consistent with these results analysis of pronase glycopeptides from cells labeled with [14C]glucosamine showed a strong decrease of sialylated complex-type oligosaccharides and a dramatic accumulation of the neutral mannose-rich chains. The latter chains predominate in partially glycosylated precursors, whereas the complex acidic chains predominate in the fully processed forms of HSV glycoproteins. These results taken together indicate that (i) host-cell N-acetylglucosaminyl transferase I participates in the processing of HSV glycoproteins; and (ii) infectivity of herpesvirions does not necessarily require the mature form of gB. The absence of HSV-1(MP)-induced fusion in RicR14 cells is discussed.

Herpesvirus-induced "early" glycoprotein: characterization and possible role in immune cytolysis

Glycoprotein GVP-11 (molecular weight, 71,500), induced by bovine herpesvirus type 1, was detected on the external surface of infected cells. It could be categorized as an "early" or "beta" class protein since it was synthesized early in the infectious process and its expression was not dependent upon prior viral DNA replication in the infected cells. Monoclonal antibodies directed against GVP-11 immunoprecipitated that glycoprotein and some low-molecular-weight polypeptides from infected cells labeled with either [35S]methionine or [3H]glucosamine. Immunoprecipitation of extracts from cells surface labeled with 125I yielded an additional 138,000-molecular-weight polypeptide. Tunicamycin- or bromovinyl deoxyuridine-treated infected cells yielded polypeptides that were smaller in size than corresponding glycoproteins in untreated cells. Tunicamycin-sensitive glycosylation appeared to be necessary for the expression of the glycoproteins on the surface of the infected cells. The monoclonal antibodies directed against GVP-11 and serum from an immune cow could participate in antibody- and complement-mediated immunocytolysis of infected cells, and this immunocytolysis could be enhanced by arresting cells in the early phase of viral gene expression by treatment with inhibitors of viral DNA synthesis.

Monensin inhibits the processing of herpes simplex virus glycoproteins, their transport to the cell surface, and the egress of virions from infected cells

HEp-2 cells or Vero cells infected with herpes simplex virus type 1 were exposed to the ionophore monensin, which is thought to block the transit of membrane vesicles from the Golgi apparatus to the cell surface. We found that yields of extracellular virus were reduced to less than 0.5% of control values by 0.2 microM monensin under conditions that permitted accumulation of cell-associated infectious virus at about 20% of control values. Viral protein synthesis was not inhibited by monensin, whereas late stages in the post-translational processing of the viral glycoproteins were blocked. The transport of viral glycoproteins to the cell surface was also blocked by monensin. Although the assembly of nucleocapsids appeared to be somewhat inhibited in monensin-treated cells, electron microscopy revealed that nucleocapsids were enveloped to yield virions, and electrophoretic analyses showed that the isolated virions contained immature forms of the envelope glycoproteins. Most of the virions which were assembled in monensin-treated cells accumulated in large intracytoplasmic vacuoles, whereas most of the virions produced by and associated with untreated cells were found attached to the cell surface. Our results implicate the Golgi apparatus in the egress of herpes simplex virus from infected cells and also suggest that complete processing of the viral envelope glycoproteins is not essential for nucleocapsid envelopment or for virion infectivity.

Effect of tunicamycin on the synthesis of herpes simplex virus type 1 glycoproteins and their expression on the cell surface

Herpes simplex virus specifies five glycoproteins which have been found on the surface of both the intact, infected cells and the virion envelope. In the presence of the drug tunicamycin, glycosylation of the herpes simplex virus type 1 glycoproteins is inhibited. We present in this report evidence that the immunologically specificity of the glycoproteins designated gA, gB, and gD resides mainly in the underglycosylated "core" proteins, as demonstrated by the immunoblotting technique. We showed also that tunicamycin prevented exposure of the viral glycoproteins on the cell surface, as the individual glycoproteins lost their ability to participate as targets for the specific antibodies applied in the antibody-dependent, cell-mediated cytotoxicity test. Immunocytolysis was reduced between 73 and 97%, depending on the specificity of the antibodies used. The intracellular processing of the herpes simplex virus type 1-specific glycoprotein designated gC differed from the processing of gA, gB, and GD, as evidenced by the identification of an underglycosylated but immunochemically modified form of gC on the surface of infected cells grown in the presence of tunicamycin.

Herpesvirus glycoprotein synthesis and insertion into plasma membranes

In the presence of the antibiotic tunicamycin (TM), glycosylation of herpes simplex virus glycoproteins is inhibited and non-glycosylated polypeptides analogous to the glycoproteins are synthesized (Pizer et al., J. Virol. 34:142-153, 1980). The synthesis of viral proteins and DNA occurs in TM-treated cells. By electron microscopy, nucleocapsids can be observed both in the nucleus and the cytoplasm of TM-treated cells; a small number of enveloped virions were observed on the cell surface. Analyses of the proteins in partially purified virus readily detects viral glycoproteins in the control cells, but neither glycoproteins nor nonglycosylated polypeptide analogs were observed in the virus prepared from TM-treated cells. By labeling the surface of infected cells with 125I, viral glycoproteins were detected as soon as 90 min after infection even when protein synthesis was inhibited with cycloheximide and glycosylation was blocked with TM. Labeling the proteins synthesized in infected cells with [35S]methionine showed that the surface glycoproteins detected in the cycloheximide- and TM-treated cells were not synthesized de novo after infection, but were placed on the cell surface by the infecting virus. Studies with metabolic inhibitors and a temperature-sensitive mutant blocked early in the infectious cycle showed that glycoproteins gA/gB and gD were synthesized soon after infection, but that the synthesis of gC was delayed. Under conditions of infection, in which gC and its precursor pgC are not produced, we have been able to observe the relationships between the glycosylated polypeptides that correspond to pgA/pgB and the nonglycosylated analog made in the presence of TM.

O-glycosidic carbohydrate-peptide linkages of Herpes simplex virus glycoproteins

Electrophoretically purified HSV-specified glycoproteins with radiolabelled carbohydrates were subjected to mild alkaline borohydride treatment (0.5 M NaOH and 0.5 M NaBH4). The treatment liberated significant amounts of the labelled oligosaccharides. The latter demonstrated molecular weights of about 3,000 as determined by gel filtration. The glycoproteins involved probably belong to the gA/gB complex or gC. The results suggest that HSV specified glycoproteins contain oligosaccharides linked with an O-glycosidic bond to a threonine or serine residue of the polypeptide.

Studies on benzhydrazone, a specific inhibitor of herpesvirus glycoprotein synthesis. Size distribution of glycopeptides and endo-beta-N-acetylglucosaminidase-H treatment

Benzhydrazone is a bis-amidinohydrazone derivative which specifically hinders the formation of herpes simplex virus (HSV) glycoproteins. In this study we present some structural features of the oligosaccharide chains of herpesvirus glycoproteins synthesized in cells incubated with the inhibitor. Gel filtration analysis of glycopeptides, obtained through exhaustive pronase-digestion of infected cells after a long or a short labeling with 14C-glucosamine, showed that benzhydrazone reduced the appearance of glycopeptides of all the size-classes, including the mannose-rich glycopeptide with an approximate molecular weight of 1500. The same percent of label was released from both untreated and benzhydrazone-treated cells after digestion with endo-beta-N-acetylglucosaminidase H, an enzyme which cleaves between the N-acetylglucosamine residues in large high-mannose type oligosaccharides. This indicates that the relative amount of glycoproteins sensitive to this enzyme did not differ in the two kinds of samples. PAGE analysis confirmed that the same glycoproteins were digested in both samples. They were gA, pgC, and pgD, which therefore contain high-mannose type oligosaccharides. It is concluded that benzhydrazone hinders carbohydrate addition to herpesvirus proteins at an early step.

Monoclonal antibodies to two glycoproteins of herpes simplex virus type 2

Monoclonal antibodies to herpes simplex virus type 2 were found to precipitate different numbers of radiolabeled polypeptides from lysates of virus-infected cells. Antibodies directed against two viral glycoproteins were characterized. Antibodies from hybridoma 17 alpha A2 precipitated a 60,000-molecular-weight polypeptide which chased into a 66,000- and 79,000-molecular-weight polypeptide. All three polypeptides labeled in the presence of [3H]glucosamine and had similar tryptic digest maps. The 60,000-molecular-weight polypeptide also chased into a 31,000-molecular-weight species which did not label with [3H]glucosamine. Antibodies from hybridoma 17 beta C2 precipitated a 50,000-molecular-weight polypeptide which chased into a 56,000- and 80,000-molecular weight polypeptide. These polypeptides also shared a similar tryptic digest map and labeled with [3H]glucosamine. Both monoclonal antibodies were herpes simplex virus type 2 specific. The viral proteins precipitated by 17 alpha A2 antibodies had characteristics similar to those reported for glycoprotein E, whereas the proteins precipitated by 17 beta C2 antibodies appeared to represent a glycoprotein not previously described. This glycoprotein should be tentatively designated glycoprotein F.

Synthesis and processing of glycoproteins gD and gC of herpes simplex virus type 1

Herpes simplex virus type 1 (HSV-1) contains five glycoproteins, designated gA, gB, gC, gD, and gE. The present studies focused on the synthesis and processing of two of these, gC and gD. By using monoprecipitin antibody to gC, we demonstrated an antigenic and structural relationship between the precursor, pgC(110), and the product, gC(130). Tryptic peptide analysis showed that pgC and gC shared methionine peptides and that these molecules had the same fingerprint pattern as that of gC(130) extracted from the purified virion. These results suggested that post-translational processing of gC involved no major changes in methionine-containing tryptic peptides or in the cleavage sites required to generate those peptides. The syntheses of gC and gD were compared. We found that the glycoproteins were synthesized starting at different times in the infectious cycle; pgD was detected by 2 h postinfection, whereas pgC was first detected at 4 to 6 h postinfection. Both precursor molecules, pgC(110) and pgD(52), are basic glycopolypeptides, and in both cases processing involved changes in molecular weight and charge. These changes were detected by two-dimensional gel electrophoresis. Both glycoproteins exhibited heterogeneity, displayed as a series of spots (6 for gD and 15 to 20 for gC) of increasing negative charge and molecular weight. Neuraminidase treatment decreased the size, number, and acidic charge of the spots, suggesting that processing was due in part, but not entirely, to addition of sialic acid to pgD and pgC.

Glucosamine metabolism of herpes simplex virus infected cells. Inhibition of glycosylation by tunicamycin and 2-deoxy-D-glucose

The formation of glucosamine-containing cell surface glycoproteins of herpes simplex virus (HSV) infected BMK cells was studied. Tunicamycin (TM) and 2-deoxy-D-glucose (DG) were used as inhibitors. With both inhibitors the multiplication of HSV was inhibited. DG markedly reduced cellular uptake of radioactively labelled glucosamine while TM interfered with the processing of glucosamine into TCA-insoluble material. Gel filtration chromatography on Sephadex G50 gel of cell surface material released by trypsin and further prepared by digestion with pronase indicated that TM and DG reduced the apparent high molecular weights of virus induced surface glycoproteins. In presence of DG the accumulation of a class of glucosamine-containing heterosaccharides (MW less than 3000) not present on DG-free HSV infected cells was observed. In TM treated cells virtually all surface heterosaccharides with molecular weights exceeding 3000 and containing glucosamine disappeared. Moreover, a component compatible with a lipid-linked oligosaccharide present in DG treated cells was not observed in HSV infected TM treated cells. The results exemplifies some different steps in glucosamine metabolism of virus induced cell surface glycoproteins differently affected by tunicamycin and 2-deoxy-D-glucose.

Selective inhibition of herpes simplex virus glycoprotein synthesis by a benz-amidinohydrazone derivative

1H-benz[f]indene-1.3(2H)dione-bis-amidinohydrazone (benzhydrazone) inhibited incorporation of 14C-glucosamine, 14C-fucose and 14C-mannose into glycoproteins of HEp-2 cells infected with various strains of herpes simplex virus 1 (HSV-1) and impaired RNA and protein synthesis to a low extent. These biochemical effects are very similar to those induced by glycosylation inhibitors such as tunicamycin, D-glucosamine and 2-deoxy-D-glucose. In contrast to these inhibitors, benzhydrazone reduced HSV glycoprotein synthesis selectively since it did not significantly modify i) the saccharide uptake into glycoproteins of uninfected and of Sindbis virus-infected cells, ii) viral growth and cell fusion in paramyxovirus-infected cells, two activities which depend on viral glycoprotein synthesis. Benzhydrazone had only minor effects on the overall metabolism of uninfected cells, since it did not alter cell growth rate, and amino acid, uridine, and hexose incorporations were about 80% those of untreated cells.

Herpes simplex virus phosphoproteins. II. Characterization of the virion protein kinase and of the polypeptides phosphorylated in the virion

The protein kinase associated with purified herpes simplex virus 1 and 2 virions partitioned with the capsid-tegument structures and was not solubilized by non-ionic detergents and low, non-inhibitory concentrations of urea. The enzyme required Mg2+ or Mn2+ and utilized ATP or GTP. The activity was enhanced by non-ionic detergents and by Na+ even in the presence of high concentrations of of Mg2+, but not by cyclic nucleotides. The enzyme associated with capsid-tegument structures phosphorylated virion polypeptides only; exogenously added substrates (acidic and basic histones, casein, phosphovitin, protamine, and bovine serum albumin) were not phosphorylated. The major phosphorylated species were virion polypeptides (VP) 1-2, 4, 11-12, 13-14, 18.7, 18.8 and 23. VP 18.7 and VP 18.8 have not been previously detected, but may be phosphorylated forms of polypeptides co-migrating with VP 19. Of the remainder, only VP 23 has been previously identified as a capsid protein; the others are constituents of the tegument or of the under surface of the virion envelope. The distribution of the phosphate bound to viral polypeptides varied depending on the Mg2+ concentration and pH. In the absence of dithiothreitol, in vitro phosphate exchange was demonstrable in VP 23 and to a lesser extent in two other polypeptides on sequential phosphorylation frist with saturating amounts off unlabeled ATP and then with [gamma-32P]ATP. Analysis of the virion polypeptides specified by herpes simplex virus 1 X herpes simplex virus 2 recombinants indicates that the genes specifying the polypeptides which serve as a substrate for the protein kinase map in the unique sequences near the left and right reinterated DNA sequences of the L component.

Alterations in glycoprotein gB specified by mutants and their partial revertants in herpes simplex virus type 1 and relationship to other mutant phenotypes

The tsB5 mutant of herpes simplex virus type 1 (HSV-1) strain HFEM was shown previously to be temperature sensitive for accumulation of the mature form of glycoprotein gB, for production or activity of a factor required in virus-induced cell fusion, and for production of virions with normal levels of infectivity. In addition, a previous study showed that virions produced by tsB5 at permissive temperature were more thermolabile than HFEM virions and contained altered gB that did not assume the dimeric conformation characteristic of HFEM. Results presented here demonstrate that, at permissive temperature, tsB5 differs from HFEM in another respect: plaques formed by tsB5 are syncytial on Vero cells (but not on HEp-2 cells), whereas plaques formed by HFEM are nonsyncytial on both cell types. In addition, our results indicate that tsB5 produces an oligomeric form of gB, but that it differs in electrophoretic mobility and stability from the gB dimers of HFEM. The major purpose of this study was to investigate the dependence of the various tsB5 mutant phenotypes on the temperature sensitivity of gB accumulation and on the alterations in oligomeric conformation of gB produced at permissive temperature. For this work the following HSV-1 strains related to tsB5 or HFEM were analyzed: (i) phenotypic revertants selected from tsB5 stocks for nonsyncytial plaque morphology on Vero cells or for ability to form plaques at restrictive temperature (38.5 degrees C); (ii) a plaque morphology variant of HFEM selected for its syncytial phenotype on Vero cells; (iii) temperature-sensitive recombinants previously isolated from a cross between tsB5 and the non-temperature-sensitive syncytial strain HSV-1(MP); and (iv) a phenotypic revertant selected from one of the recombinant stocks for its ability to form plaques at 39 degrees C. These strains were all compared with tsB5 and HFEM at three different temperatures in two different cell lines with respect to plaque formation, yield of infectious progeny, virus-induced cell fusion, and accumulation of gB. The results of our analyses on all the strains tested revealed the following correlations between mutant phenotypes and the accumulation and oligomeric conformation of gB. (i) There was a direct and quantitative relationship between the accumulation in infected cells of infectious progeny and of the mature form of gB, providing strong support for the hypothesis that this form of gB is necessary to the production of infectious virions. The oligomeric conformation of gB characteristic of HFEM is apparently not required for virion infectivity; nor was virion thermostability necessarily related to the presence of the HFEM-like oligomeric form of gB. (ii) The previously reported correlation between temperature sensitivity of gB accumulation and virus-induced cell fusion was confirmed for tsB5 and extended to other virus strains, and coordinate reversion of these traits was also demonstrated, providing support for the hypothesis that gB has a role in virus-induced cell fusion. At 37 degrees C, intermediate between permissive and restrictive temperatures, some of the mutants and partial revertants induced cell fusion despite reduced accumulations of the mature form of gB, suggesting that the amount of mature gB present did not determine the extent of fusion and that other forms of gB as well as other factors should be investigated with regard to the process of cell fusion. (iii) Some of the mutants and partial revertants could form plaques at 38.5 degrees C despite reduced accumulations of gB and infectious progeny, indicating that the cell-to-cell transmission of viral infection may be at least in part independent of these factors.

Recombination and linkage between structural and regulatory genes of herpes simplex virus type 1: study of the functional organization of the genome

Phenotypic and genetic properties of 12 markers in structural and regulatory functions of herpes simplex virus type 1 were characterized, and their recombination and segregation behavior was investigated and interpreted with reference to available information on their physical locations. The markers were: (i) ts markers in a structural glycoprotein (tsB5) and in alpha (immediate early; tsLB2, tsc75) or beta (early, delayed early; tsB1) functions with regulatory effects; together with (ii) plaque morphology (syn), phosphonoacetate resistance (Pr), and thymidine kinase (TK) phenotypes; and (iii) electrophoretically distinct variants of glycosylated (glycoprotein C, gpC; ICP10) and non-glycosylated [VP(13-14), VP23] structural and nonstructural [ICP(47-48)] polypeptides. Mean two-factor recombination frequencies ranged from 2% (for noncomplementing mutants tsLB2 and tsc75) to 35 to 40% (for unlinked markers) and were influenced by the relative contributions of parental viruses to the mixed infection. Even with control of this variable, standard deviations of mean measures of recombination frequency ranged from a minimum of 14% (with n greater than or equal to 10) to 65% (with n = 3) of mean values; no recombination frequencies higher than 55% were observed. Differences in mean two-factor recombination frequencies between a small number of loosely linked markers were, therefore, not reliable measures of real differences in linkage. Measurements of the segregation of unselected markers among recombinant progeny were, therefore, used as measures of linkage. These experiments (i) established a linkage group for markers in the long unique region of the genome additional to, but consistent with, existing physical data, i.e., TK-syn-tsB5-(tsB1.Pr)-[gpC.VP(13-14)]; (II) identified markers, e.g., ICP(47-48), linked to regulatory mutations (tsLB2, tsc75) in redundant DNA sequences; and (iii) used the segregation of these regulatory mutations and linked markers among unselected progeny to demonstrate the linkage groups: Pr-syn-TK-tsc75-ICP(47-48), [VP(13-14).gpC]-Pr-syn-TK, and TK-tsc75-[VP(13-14).gpC]. These results were most simply explained if bi- or intermolecular recombination occurred between circular molecules or molecules catenated "head-to-tail" and were incompatible with intermolecular recombination as the mechanism of isomerization of herpes simplex virus DNA.

Effect of tunicamycin on herpes simplex virus glycoproteins and infectious virus production

The antibiotic tunicamycin, which blocks the synthesis of glycoproteins, inhibited the production of infectious herpes simplex virus. In the presence of this drug, [14C]glucosamine and [3H]mannose incorporation was reduced in infected cells, whereas total protein synthesis was not affected. Gel electrophoresis of [2-3H]mannose-labeled polypeptides failed to detect glycoprotein D or any of the other herpes simplex virus glycoproteins. By use of specific antisera we demonstrated that in the presence of tunicamycin the normal precursors to viral glycoproteins failed to appear. Instead, lower-molecular-weight polypeptides were found which were antigenically and structurally related to the glycosylated proteins. Evidence is presented to show that blocking the addition of carbohydrate to glycoprotein precursors with tunicamycin results in the disappearance of molecules, possibly due to degradation of the unglycosylated polypeptides. We infer that the added carbohydrate either stabilizes the envelope proteins or provides the proper structure for correct processing of the molecules needed for infectivity.

Structural analysis of precursor and product forms of type-common envelope glycoprotein D (CP-1 antigen) of herpes simplex virus type 1

The type-common CP-1 antigen of herpes simplex virus type 1 (HSV-1) is associated in the infected cell with two components, a 52,000-molecular-weight glycoprotein (gp52 or pD) and a 59,000-molecular-weight glycoprotein (gp59 or D). The larger form (D) is also found in the virion envelope. It was postulated that pD is a precursor of D. We found that pD shared methionine and arginine tryptic peptides with D isolated from infected cell extracts. D isolated from infected extracts had the same trypric methionine peptide profile as D isolated from the virion envelope. Thus, processing of pD to D does not involve any major alterations in polypeptide structure. Furthermore, D did not share tryptic methionine peptides with the other major glycoproteins of HSV-1. Using [2-3H]mannose as a specific glycoprotein label, we found that pD, which is a basic protein (isoelectric point = 8.0) contained a 1,800-molecular-weight oligomannosyl core moiety and was processed by further glycosylation and sialyation to a more acidic and heterogeneous molecule D, which as a molecular weight of at least 59,000.

Histopathology and histochemistry of the superficial corneal epithelium in experimental herpes simplex keratitis

Three days after herpes simplex virus inoculation, an increased amount of DNA and RNA was observed in the superficial epithelium cells of rabbit cornea. Histochemical staining demonstrated the development of acid mucopolysaccharides and the destruction of reticulin. In the early stages, on rare occasions, giant polykaryocytes with multiple micronuclei were seen. From 1 week after infection, more and more cells became rounded and shrunken. Cytoplasm of these cells might contain DNA diffusely interspersed with RNA. This DNA is probably viral in nature. The nuclei of these cells varied in shape, size, and staining intensity. Nuclear fragments were often observed in the cytoplasm. Stainings for acid mucopolysaccharides were strongly positive in the rounded cells. These cells fused to form syncytia Variable-sized pseudopodialike processes containing DNA and RNA extend from some of the rounded and liquefied cells toward other cells. In the later stages, development of ghost cells was seen. Histochemical methods demonstrated the deposition of acid mucopolysaccharides on their cell membranes. Necrosis was more often present in the late stages. Nuclear debris and deformed cells were encountered in such areas. On the healing of the keratitis, 3 months after inoculation, the cell cytology and staining reactions reverted to normal.

Molecular genetics of herpes simplex virus. II. Mapping of the major viral glycoproteins and of the genetic loci specifying the social behavior of infected cells

We have mapped the location in herpes simplex virus (HSV) DNA of (i) three mutations at different loci (syn loci) which alter the social behavior of infected cells from clumping of rounded cells to polykaryocytosis, (ii) a mutation which determines the accumulation of one major glycoprotein [VP8.0(C(2))], and (iii) the sequences encoding four major virus glycoproteins [VP8.0(C(2)), VP7(B(2)), VP8.5(A), and VP19E(D(2))]. The experimental design and results were as follows. (i) Analysis of HSV-1 x HSV-2 recombinants showed that the sequences encoding the VP19E(D(2)) glycoprotein map in the S component, whereas the sequences encoding the other three major glycoproteins are in two locations in the L component of HSV DNA. The templates specifying the HSV-1 and HSV-2 glycoprotein VP8.0(C(2)) appear not to be colinear; we isolated recombinants specifying glycoproteins comigrating in sodium dodecyl sulfate-polyacrylamide gels with VP8.0(C(2)) of both HSV-1 and HSV-2. (ii) Marker rescue of a ts mutant defective in accumulation of glycoprotein VP7(B(2)) showed that the mutation maps within a region containing the sequences encoding that glycoprotein. (iii) Marker transfer experiments involving transfection of rabbit skin cells with donor HSV-1(F) DNA and fragments from several donor strains causing fusion of Vero or both Vero and HEp-2 cells revealed the existence of three syn loci specifying the social behavior of cells and one locus (Cr) determining the accumulation of glycoprotein VP8.0(C(2)). The Cr locus maps to the right of the template specifying VP8.0(C(2)) glycoprotein. Loci syn 1 and syn 2 map at or near the Cr locus but can be segregated from it. Locus syn 3 maps at or near the template specifying glycoproteins VP7(B(2)) and VP8.5(A). The expression of mutations in the syn 1 and syn 3 loci appear to be cell type dependent, in that recombinants with these mutations fuse Vero cells but not HEp-2 cells. Recipients of the syn 2 locus or of both syn 2 and syn 1 loci fuse both Vero and HEp-2 cells.