Location of the structural genes for glycoproteins gD and gE and for other polypeptides in the S component of herpes simplex virus type 1 DNA

Binding of human and animal immunoglobulins to the IgG Fc receptor induced by human cytomegalovirus

Human cytomegalovirus (HCMV)-infected cells express a virus-encoded receptor that is able to bind the Fc part of IGG: Some basic binding properties of this Fc receptor (FcR) have been examined. The affinity constant (K(a)) for human IgG Fc fragment in its interaction with acetone-fixed, HCMV-infected human embryonic lung fibroblasts was estimated to be around 2 x 10(8) M(-1) and the number of binding sites was estimated to be around 2 x 10(6) per cell. Of the human IgG, IgA, IgM and IgD classes, only IgG reacted with the receptor, and all four of the IgG subclasses were reactive. IgG from rabbit, hamster, cat, swine and horse exhibited binding to the HCMV FcR, in contrast to IgG from mouse, rat, guinea pig, dog, sheep, goat, cow and chicken. Immunoglobulins with and without HCMV IgG FcR-binding properties, like IgG from rabbit and mouse, can be of value in revealing the functional importance of the receptor. When the immunoglobulins were tested against herpes simplex virus type 1-induced FcR, both similarities and differences in immunoreactivity were seen relative to the HCMV FcR, which makes it unlikely that the binding sites for these two herpesvirus FcRs on the IgG molecule are identical.

A herpes simplex virus 1 recombinant lacking the glycoprotein G coding sequences is defective in entry through apical surfaces of polarized epithelial cells in culture and in vivo

During infection of a new host, the first surfaces encountered by herpes simplex viruses are the apical membranes of epithelial cells of mucosal surfaces. These cells are highly polarized, and the protein composition of their apical and basolateral membranes are very different, so that different viral entry pathways have evolved for each surface. To determine whether the viral glycoprotein G (gG) is specifically required for efficient infection of a particular surface of polarized cells, apical and basal surfaces were infected with wild-type virus or a gG deletion mutant. After infection of polarized cells in culture, the gG(-) virus was deficient in infection of apical surfaces but was able to infect cells through basal membranes, replicate, and spread into surrounding cells. The gG-dependent step in apical infection was a stage beyond attachment. After in vivo infection of apical surfaces of epithelial cells of nonscarified mouse corneas, infection by glycoprotein C(-) or gG(-) virus was considerably reduced as compared with that observed after infection with wild-type virus. In contrast, when corneas were scarified, allowing virus access to other cell surfaces, the gG and glycoprotein C deletion mutants infected eyes as efficiently as wild-type viruses. A secondary mutation allowing infection of apical surfaces by gG(-) virus arose readily during passage of the virus in nonpolarized cells, indicating that either the gG-dependent step of apical infection can be bypassed or that another viral protein can acquire the same function.

Vaccination with a cocktail of seven recombinantly expressed HSV-1 glycoproteins protects against ocular HSV-1 challenge more efficiently than vaccination with any individual glycoprotein

Our previous studies have shown that of seven HSV-1 glycoproteins (gB, gC, gD, gE, gG, gH and gI) individually expressed in baculovirus, vaccination with gD provides the best protection against HSV-1 challenge. To establish whether vaccination with a mixture of these seven expressed glycoproteins would provide better protection against HSV-1 challenge than vaccination with gD alone, we determined the level of protection afforded by vaccination with a cocktail of the seven expressed glycoproteins. The amount of each of the seven expressed glycoproteins in the mixture was equivalent to one-seventh the amount of gD used in the gD alone vaccination. Thus, the total amount of glycoprotein was the same for the cocktail and gD alone vaccine. For neutralizing antibody titer, delayed-type hypersensitivity (DTH), and survival following lethal challenge, no difference was observed between mice vaccinated with all seven glycoproteins and those vaccinated with gD. However, for other criteria, vaccination with all seven glycoproteins appeared to provide better protection than vaccination with gD. Following ocular challenge, virus was not detected at any time in the tears of mice vaccinated with all seven glycoproteins. In contrast, virus was detected in the tears of gD vaccinated mice for up to 3 days post challenge. Mock vaccinated mice had virus in their tears for as long as 10 days. Mice vaccinated with all seven glycoproteins had no eye disease, while gD vaccinated mice had a significant amount of blepharitis. Finally, compared to gD vaccinated mice, the mice vaccinated with all seven glycoproteins were more efficiently protected against the establishment of HSV-1 latency following ocular infection. Our results therefore suggest that while for some protective criteria there was no significant difference between vaccination with gD or seven glycoproteins, vaccination with seven glycoproteins was more efficient in protecting challenged mice against some forms of eye disease, the duration of infection and the establishment of latency.

Fv structure of monoclonal antibody II-481 against herpes simplex virus Fc gamma-binding glycoprotein gE contains immunodominant complementarity determining region epitopes that react with human immunoglobulin M rheumatoid factors

Human immunoglobulin M (IgM) rheumatoid factors (RFs) show primary direct enzyme-linked immunosorbent assay (ELISA) reactivity with Fab rather than Fc fragments of monoclonal antibody (mAb) II-481 directed against the Fc gamma-binding site of herpes simplex virus glycoprotein gE. This preferential anti-Fab specificity suggests that RFs react with antigen-binding portions of mAb II-481 as anti-idiotypic antibodies directed at the combining site regions of mAb reacting with the Fc gamma-binding region of gE. Analysis of this idiotype-anti-idiotype reaction employed polymerase chain reaction amplification and sequencing of the variable heavy and light (VH and VL) regions of mAb II-481. When VH and VL regions of mAb II-481 were synthesized as overlapping 7-mer peptides on polypropylene pins, a panel of 10 polyclonal and 6 monoclonal human IgM RFs reacted primarily with epitopes within the three solvent-exposed mAb II-481 complementarity determining regions (CDRs). Preincubation of single CDR heptamer peptides with IgM RFs in free solution, resulted in 63-100% inhibition of RF binding to mAb II-481 on the ELISA plate, confirming the antigenic importance of linear CDR regions for RF reactivity. Combinations of two or three CDR peptides frequently produced 94-100% inhibition of RF binding to whole mAb II-481. Control peptides, singly or in combination, showed no inhibition. Computer modeling suggested that the RF-reactive mAb II-481 Fv region and a previously demonstrated RF-reactive CH3 epitope displayed considerable three-dimensional similarities in conformation. These studies may provide insight into limited shape homologies possibly involved in an RF anti-idiotypic reaction.

The herpes simplex virus type 1 particle: structure and molecular functions. Review article

This review is a summary of our present knowledge with respect to the structure of the virion of herpes simplex virus type 1. The virion consists of a capsid into which the DNA is packaged, a tegument and an external envelope. The protein compositions of the structures outside the genome are described as well as the functions of individual proteins. Seven capsid proteins are identified, and two of them are mainly present in precursors of mature DNA-containing capsids. The protein components of the 150 hexamers and 12 pentamers in the icosahedral capsid are known. These capsomers all have a central channel and are connected by Y-shaped triplexes. In contrast to the capsid, the tegument has a less defined structure in which 11 proteins have been identified so far. Most of them are phosphorylated. Eleven virus-encoded glycoproteins are present in the envelope, and there may be a few more membrane proteins not yet identified. Functions of these glycoproteins include attachment to and penetration of the cellular membrane. The structural proteins, their functions, coding genes and localizations are listed in table form.

Identification of functional regions of herpes simplex virus glycoprotein gD by using linker-insertion mutagenesis

Glycoprotein gD is a component of the herpes simplex virus (HSV) envelope essential for virus entry into susceptible cells. Previous studies using deletion and point mutations identified a functional domain of HSV-1 gD (gD-1) from residues 231 to 244. However, many of the deletion mutations had global effects on gD-1 structure, thus precluding assessment of the functional role of large portions of the protein. In this study, we constructed a large panel of linker-insertion mutants in the genes for gD-1 and HSV-2 gD (gD-2). The object was to create mutations which would have only localized effects on protein structure but might have profound effects on gD function. The mutant proteins were expressed in transiently transfected L cells. Monoclonal antibodies (MAbs) were used as probes of gD structure. We also examined protein aggregation and appearance of the mutant glycoproteins on the transfected cell surface. A complementation assay measured the ability of the mutant proteins to rescue the infectivity of the gD-null virus, FgD beta, in trans. Most of the mutants were recognized by one or more MAbs to discontinuous epitopes, were transported to the transfected cell surface, and rescued FgD beta virus infectivity. However, some mutants which retained structure were unable to complement FgD beta. These mutants were clustered in four regions of gD. Region III (amino acids 222 to 246) overlaps the region previously defined by gD-1 deletion mutants. The others, from 27 through 43 (region I), from 125 through 161 (region II), and from 277 to 310 (region IV), are newly described. Region IV, immediately upstream of the transmembrane anchor sequence, was previously postulated to be part of a putative stalk structure. However, residues 277 to 300 are directly involved in gD function. The linker-insertion mutants were useful for mapping MAb AP7, a previously ungrouped neutralizing MAb, and provided further information concerning other discontinuous epitopes. The mapping data suggest that regions I through IV are physically near each other in the folded structure of gD and may form a single functional domain.

Adjuvant-independent enhanced immune responses to recombinant herpes simplex virus type 1 glycoprotein D by fusion with biologically active interleukin-2

A truncated herpes simplex virus (HSV) type 1 glycoprotein D (t-gD) gene was fused to the human interleukin-2 (IL-2) gene (t-gD-IL-2 gene) and introduced into mouse myeloma Sp2/0 cells. The gene product, t-gD-IL-2, secreted from the cells was immunoprecipitated with five monoclonal antibodies specific for native gD. Purified t-gD-IL-2 supported the growth of IL-2-dependent cells, with a specific activity almost comparable to that of recombinant human IL-2. Mice immunized with t-gD-IL-2 in an adjuvant-free form showed superior anti-HSV antibody responses, and were completely protected against HSV challenge, whereas immunization with t-gD adsorbed onto aluminum hydroxide (alum) partially failed to prevent the virus infection. The high immunogenicity of t-gD-IL-2 was due to the biological activity of the fused IL-2 rather than to a hapten-carrier effect of the IL-2 moiety, because mice primed with t-gD-IL-2 showed delayed-type hypersensitivity against stimulation with gD, but not against that with IL-2 antigen, and because a booster immunization with t-gD-IL-2 extensively augmented the response of anti-gD antibody, but not that of the anti-human IL-2 antibody. The serological half-life of IL-2 activity in mice injected with t-gD-IL-2 was prolonged to about four times that of rIL-2. However, when t-gD-IL-2 was co-administered with human albumin (HSA), the mouse anti-HSA antibody response was slightly enhanced.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification and characterization of an equine herpesvirus 1 late gene encoding a potential zinc finger

In this report, we present the DNA sequence and transcriptional characterization of a gene (IR5) that maps within each of the inverted repeat (IR) segments of the equine herpesvirus type 1 (EHV-1) genome. The IR5 open reading frame (ORF) is located within both IR sequences (nucleotides 9932-10,642 of the IR). DNA sequence analyses of the IR5 gene region revealed an ORF of 236 amino acids (24,793 Da) that showed significant homology to ORF64 of varicella-zoster virus and ORF3 of EHV-4 both of which map within the inverted repeats and to the US10 ORF of herpes simplex virus type 1 (HSV-1) which maps within the unique short segment. Additional analyses of the nucleotide sequence failed to reveal any overlapping ORFs that would correspond to US11 or US12 of HSV-1. Interestingly, the IR5 ORF of EHV-1 possesses a sequence of 13 amino acids (CAYWCCLGHAFAC) that is a perfect match to the consensus zinc finger motif (C-X2-4-C-X2-15-C/H-X2-4-C/H). Putative cis-acting elements flanking the IR5 ORF include a TATA box (nucleotides 9864-9870), a CAAT box (nucleotides 9709-9714), and a polyadenylation signal (nucleotides 10,645-10,650). Northern blot and S1 nuclease analyses identified a single 0.9-kb mRNA species that first appears at 2 hr postinfection, and whose synthesis is reduced in the presence of phosphonoacetic acid, an inhibitor of EHV-1 DNA synthesis. Thus, the IR5 gene of EHV-1 exhibits characteristics representative of a late gene of the gamma-1 class. The characterization of the IR5 gene at the DNA and RNA levels will facilitate ongoing studies to identify and characterize the IR5 polypeptide.

Baculovirus-expressed glycoprotein E (gE) of herpes simplex virus type-1 (HSV-1) protects mice against lethal intraperitoneal and lethal ocular HSV-1 challenge

We have constructed a recombinant baculovirus expressing high levels of the herpes simplex virus type 1 (HSV-1) glycoprotein E (gE) in Sf9 cells. The expressed gE migrated on gels as a double band with apparent molecular weights of 68 and 70 kDa. The recombinant gE was glycosylated based on its susceptibility to tunicamycin treatment and was transported to the membrane of Sf9 cells based on indirect immunofluorescence. Mice vaccinated with gE developed high serum titers of HSV-1-neutralizing antibodies based on plaque reduction assays. gE vaccination also induced a strong delayed type hypersensitivity (DTH) response to HSV-1. In addition, mice vaccinated with the recombinant gE were protected from both intraperitoneal and ocular lethal HSV-1 challenge. To our knowledge, this is the first report in which vaccination with gE was shown to induce high neutralizing antibody titers, a DTH response, or protection against lethal HSV-1 challenge.

Expression of herpes simplex virus type 1 glycoprotein I in baculovirus: preliminary biochemical characterization and protection studies

We have constructed a recombinant baculovirus expressing the herpes simplex virus type 1 (HSV-1) glycoprotein I (gI). Sf9 cells infected with this recombinant virus synthesized gI-related polypeptides with apparent molecular sizes of 52 and 56 kDa. The recombinant gI appeared to be glycosylated, since it was susceptible to both tunicamycin and endoglycosidase H, and the expressed gI was transported to the surface of infected cells as judged by indirect immunofluorescence. Antibodies to the recombinant gI raised in mice neutralized HSV-1 infectivity. Finally, we show here for the first time that vaccination with gI can protect mice against HSV-1 challenge.

Rheumatoid factors react with Fab fragments of monoclonal antibodies to herpes simplex virus types 1 and 2 Fc gamma-binding proteins

Human polyclonal IgM rheumatoid factors (RF) were tested in an enzyme-linked immunosorbent assay with monoclonal antibodies (MAb) (II-481 and B10/A8) to glycoprotein E (gE), the Fc gamma-binding protein of herpes simplex virus type 1 (HSV-1), as well as with MAb 88-S to gE of HSV-2. Most of the RF reacted with II-481 and 88-S. Positive reactions were recorded for RF reacting with whole MAb II-481 and 88-S, as well as with their Fab, but not their Fc, fragments. Human monoclonal IgM RF isolated from mixed cryoglobulins showed a similar profile, with reactivity for both whole MAb II-481 and 88-S and for their Fab fragments. Reactivity with MAb to gE was observed regardless of the Gm specificity of the polyclonal RF and the cross-reactive idiotypes (6B6, 17.109, or G6) of the monoclonal RF. No positive reactions were noted between protein A and Fab fragments of any of the anti-gE MAb. These findings indicate that many RF may bear the internal image of the Fc gamma-binding regions of 2 different herpesviruses: HSV-1 and HSV-2.

Immunoselection of recombinant baculoviruses expressing high levels of biologically active herpes simplex virus type 1 glycoprotein D

The DNA sequence encoding the complete herpes simplex virus type 1 (HSV-1) glycoprotein D (gD) was inserted into a baculovirus transfer vector under control of the polyhedrin gene promoter of the baculovirus Autographa california nuclear polyhedrosis virus (AcNPV). After co-transfection of Spodoptera frugiperda (Sf9) insect cells with wild-type AcNPV DNA and the recombinant transfer vector DNA, polyhedrin-negative recombinants that expressed high levels of HSV-1 gD were isolated using immunoaffinity selection with antibody coated magnetic particles followed by plaque purification. These recombinant baculoviruses expressed a protein that was slightly smaller than virion HSV-1 gD made in Vero cells. This recombinant protein was expressed at high levels. The expressed protein was glycosylated, was found on the membrane of Sf9 cells, and reacted with gD specific antibodies. Antibodies raised in mice to the recombinant gD neutralized HSV-1 as measured by plaque reduction assays. Mice inoculated with the recombinant baculovirus were completely protected from lethal challenge with HSV-1.

Sequence analysis of a glycoprotein D gene homolog within the unique short segment of the EHV-1 genome

DNA sequence analysis of one-third of the unique short (Us) segment of the equine herpesvirus type 1 (EHV-1) genome revealed an open reading frame (ORF) whose translated sequence exhibits significant homology to glycoprotein D of herpes simplex virus (HSV) types 1 and 2 and to pseudorabies virus (PRV) glycoprotein 50, the gD equivalent. The ORF of the EHV-1 gD homolog lies within the pSZ-4 BamHI/KpnI fragment (map units 0.865 to 0.872 and 0.869 to 0.884) and is capable of encoding a polypeptide of 385 amino acids (43,206 molecular weight). Analysis of the nucleotide sequence revealed a complete transcriptional unit including CAAT and TATA elements and signals for polyadenylation. The predicted protein exhibits features typical of a transmembrane protein: a hydrophobic N-terminal signal sequence followed by a probable cleavage site, four potential N-linked glycosylation sites, and a hydrophobic membrane-spanning domain near the carboxyl terminus followed by a charged membrane anchor sequence.

Glycoprotein D of herpes simplex virus encodes a domain which precludes penetration of cells expressing the glycoprotein by superinfecting herpes simplex virus

Earlier studies have shown that herpes simplex viruses adsorb to but do not penetrate permissive baby hamster kidney clonal cell lines designated the BJ series and constitutively expressing the herpes simplex virus 1 (HSV-1) glycoprotein D (gD). To investigate the mechanism of the restriction, the following steps were done. First, wild-type HSV-1 strain F [HSV-1(F)] virus was passaged blindly serially on clonal line BJ-1 and mutant viruses [HSV-1(F)U] capable of penetration were selected. The DNA fragment capable of transferring the capacity to infect BJ cells by marker transfer contains the gD gene. The mutant gD, designated gDU, differed from wild-type gD only in the substitution of Leu-25 by proline. gDU reacted with monoclonal antibodies which neutralize virus and whose epitopes encompass known functional domains involved in virus entry into cells. It did not react with the monoclonal antibody AP7 previously shown to react with an epitope which includes Leu-25. Second, cell lines expressing gDU constitutively were constructed and cloned. Unlike the clonal cell lines constitutively expressing gD (e.g., the BJ cell line), those expressing gDU were infectable by both HSV-1(F) and HSV-1(F)U. Lastly, exposure of BJ cells to monoclonal antibody AP7 rendered the cells capable of being infected with HSV-1(F). The results indicate that (i) gD expresses a specific function, determined by sequences at or around Leu-25, which blocks entry of virus into cells synthesizing gD, (ii) the gD which blocks penetration by superinfecting virus is located in the plasma membrane, (iii) the target of the restriction to penetration is the identical domain of the gD molecule contained in the envelope of the superinfecting virus, and (iv) the molecular basis of the restriction does not involve competition for a host protein involved in entry, as was previously thought.

Herpes simplex virus IgG Fc receptors induced using recombinant adenovirus vectors expressing glycoproteins E and I

Evidence has been presented that herpes simplex virus (HSV) immunoglobulin (IgG) Fc receptors are composed of a complex of two glycoproteins, gE and gI. In previous studies, cells infected with HSV-1 mutants lacking either gE or gI bound lower levels of soluble IgG than cells infected with wild-type viruses suggesting that both gE and gI were required for IgG binding. We have reevaluated the Fc receptor activity of these mutants using a more sensitive assay involving IgG-coated erythrocytes and have found that cells infected with a gE- mutant HSV-1 did not bind IgG-coated erythrocytes whereas cells infected with a gI- mutant retained some Fc binding activity. To further study HSV-induced Fc receptors recombinant adenovirus vectors expressing gE or gI were constructed. Cells expressing gE alone bound both soluble IgG and IgG-coated red cells, although the binding was consistently lower than that observed with HSV-infected cells or cells expressing both gE and gI. Cells expressing only gI were unable to bind either soluble IgG or IgG-coated erythrocytes. These results support the conclusion that both gE and gI are required for full Fc receptor activity, although gE alone can bind IgG to a lesser extent.

Induction of immunoglobulin G Fc receptors by recombinant vaccinia viruses expressing glycoproteins E and I of herpes simplex virus type 1

Glycoprotein E (gE) of herpes simplex virus type 1 (HSV-1) will bind immunoglobulin G (IgG) (Fc) affinity columns (R. B. Bauke and P. G. Spear, J. Virol. 32:779-789, 1979), but recent evidence suggests that the HSV-1 Fc receptor is composed of a complex of gE and glycoprotein I (gI) and that both gI and gE are required for Fc receptor activity (D. C. Johnson and V. Feenstra, J. Virol. 61:2208-2216, 1987; D. C. Johnson, M. C. Frame, M. W. Ligas, A. M. Cross, and N. D. Stow, J. Virol. 62:1347-1354, 1988). We have expressed gE and gI, either alone or in combination, on the surface of HeLa cells by using recombinant vaccinia viruses and have measured Fc receptor activity by Fc-rosetting or IgG-binding assays. Expression of gE alone resulted in the induction of Fc receptor activity, while expression of gI alone gave no detectable Fc binding. Coexpression of gE and gI resulted in higher levels of IgG binding than did expression of gE alone, despite the fact that under conditions of coexpression, the levels of surface gE were reduced. We propose that gE and gI together form a receptor of higher affinity than gE alone and that HSV-1 therefore has the potential to induce two Fc receptors of different affinities.

Antigenic and functional analysis of a neutralization site of HSV-1 glycoprotein D

Herpes simplex virus glycoprotein D is a component of the virion envelope and appears to be involved in attachment, penetration, and cell fusion. Monoclonal antibodies (MAbs) against this protein can be arranged in groups, on the basis of a number of biological and biochemical properties. Group I antibodies are type-common, have high complement-independent neutralization titers, recognize discontinuous (conformational) epitopes, and block each other in a binding assay. The sum of their epitopes constitutes antigenic site I of gD. Using a panel of neutralization-resistant mutants, we previously found that group I MAbs can be divided into two subgroups, Ia and Ib, such that mutations selected with Ia antibodies have little or no effect on binding and neutralization by Ib antibodies, and vice versa. Antigenic site I therefore consists of two parts, Ia and Ib. We have now identified the point mutations which prevent neutralization. Two Ib MAbs (DL11 and 4S) selected a Ser to Asn change at residue 140; this alteration creates a new N-linked glycosylation site, which is used. A third Ib MAb (D2) selected a Gln to Leu change at 132. The mutation selected by the Ia MAb HD1 (Ser to Asn at residue 216) is identical to that selected by MAb LP2, another Ia antibody. By using oligonucleotide-directed mutagenesis, we have produced gD genes with combinations of the above mutations. Attempts to recombine these genes into the virus genome were unsuccessful, suggesting that the combinations are lethal. This was confirmed by a complementation assay which measures the ability of gD transiently expressed in transfected Vero cells to rescue the production of infectious virus by the gD-minus mutant F-gD beta.

ICP4-binding sites in the promoter and coding regions of the herpes simplex virus gD gene contribute to activation of in vitro transcription by ICP4

The herpes simplex virus immediate-early gene product ICP4 activates the transcription of viral early and late genes. We characterized the DNA sequence elements of the early glycoprotein D (gD) gene that play a role in the response to ICP4 in vitro. Using gel mobility shift assays and DNase I footprinting, we identified three ICP4-binding sites, two 5' to the mRNA start site and a third within the coding region. Site II, which gave a footprint between nucleotides -75 and -111 relative to the RNA start site, was previously identified by Faber and Wilcox and contained the reported consensus ICP4-binding site. Site III, which was located between nucleotides +122 and +163, was very similar to the site II sequence, including a core consensus binding sequence, TCGTC. The site I sequence (nucleotides -308 to -282), however, did not share significant homology with either site II or site III. In vitro transcription experiments from mutant constructs of the gD promoter indicated that all three ICP4-binding sites contribute to the stimulation of transcription by ICP4. DNase I footprinting of the gD promoter with uninfected nuclear extracts of HeLa cells showed protection of two very G-rich sequences between nucleotides -33 and -75. We propose that optimal transcription of the gD gene depends on the interaction of ICP4 with multiple binding sites across the gene and cellular factors that recognize specific sequence elements in the promoter.

Analysis of the in vitro translation products of the equine herpesvirus type 1 immediate early mRNA

Equine herpesvirus type 1 (EHV-1) gene expression is coordinately regulated in an alpha, beta, gamma fashion. Viral alpha gene products include a 6.0-kb immediate early (IE) mRNA species (W. L. Gray et al., 1987, Virology 158, 79-87) and at least four closely related IE polypeptides (IEPs) (G.B. Caughman et al., 1985, Virology 145, 49-61). In this report, we describe results obtained from a series of in vitro translation experiments which were performed in an effort to characterize the IEPs and identify the mechanism by which individual IE protein species are generated. Our data indicate that a family of IEPs is generated in vitro from the 6.0-kb mRNA size class and that these IEPs correspond in overall size and antigenicity to those synthesized in infected cells. Using time-course/pulse-chase analyses, we show that production of three of the major IEPs [IE1' (193 kDa), IE3' (166 kDa), and IE4' (130 kDA)] occurs concomitantly, that none of these protein species can be chased completely into another, and that at least two additional minor species appear to be processed following synthesis. Finally, we show that the 6.0-kb mRNA species isolated during early or late stages of the infection cycle can be translated to yield all of the major IE proteins, indicating that production of the family of IEPs is not dependent upon accumulation of the IE mRNA which occurs during a cycloheximide blocked infection cycle. The implications of these findings are discussed as they relate to the origin and production of the IEPs both in vivo and in vitro.

Characterization of an equine herpesvirus type 1 gene encoding a glycoprotein (gp13) with homology to herpes simplex virus glycoprotein C

The molecular structure of the equine herpesvirus type 1 (EHV-1) gene encoding glycoprotein 13 (gp13) was analyzed. The gene is contained within a 1.8-kilobase AccI-EcoRI restriction fragment mapping at map coordinates 0.136 to 0.148 in the UL region of the EHV-1 genome and is transcribed from right to left. Determination of the nucleotide sequence of the DNA fragment revealed a complete transcriptional unit composed of typical regulatory promoter elements upstream to a long open reading frame (1,404 base pairs) that encoded a 468-amino-acid primary translation product of 51 kilodaltons. The predicted protein has the characteristic features of a membrane-spanning protein: an N-terminal signal sequence, a hydrophobic membrane anchor region, a charged C-terminal cytoplasmic tail, and an exterior domain with nine potential N-glycosylation sites. The EHV-1 DNA sequences expressed in lambda gt11 as gp13 epitopes were present in the open reading frame. Amino acid sequences composing a major antigenic site, recognized by 35% of a panel of 42 anti-gp13 monoclonal antibodies, were identified in the N-terminal surface domain of the deduced gp13 molecule. Comparison of the EHV-1 gp13 DNA sequence with that encoding glycoproteins of other alphaherpesviruses revealed no detectable homology. However, a search for homology at the amino acid level showed regions of significant sequence similarity between the amino acids of the carboxy half of EHV-1 gp13 and those of the same region of gC-like glycoproteins of herpes simplex virus (gC-1 and gC-2), pseudorabies herpesvirus (gIII), and varicella-zoster virus (gp66). The sequences of the N-terminal portion of gp13, by contrast, were much less conserved. The results of these studies indicate that EHV-1 gp13 is the structural homolog of herpes simplex virus glycoprotein C and further suggest that the epitope-containing N-terminal amino acid sequences of the herpesvirus gC-like glycoproteins have undergone more extensive evolutionary divergence than the C-terminal sequences.

Genomic location of bovid herpesvirus type 2 nucleotide sequences homologous to five herpes simplex virus type 1 genes

The location of nucleotide sequences within the bovid herpesvirus 1 (BHV-2) genome homologous to herpes simplex virus 1 (HSV-1) DNA were investigated. BHV-2 DNA was digested with restriction endonucleases and blotted to nitrocellulose paper. The blots were then probed with plasmids containing HSV-1 genes for thymidine kinase (TK), the major DNA binding protein (ICP8), the major capsid protein (VP5) and genes for HSV-1 glycoproteins gB, gD, and gC. Except for HSV-1 gC, each HSV-1 gene tested hybridized to BHV-2 nucleotide sequences that were located either on both sides of a restriction endonuclease cleavage site, within a small restriction endonuclease fragment, or to an area common to two overlapping restriction fragments. Thus, we were able to localize BHV-2 nucleotide sequences homologous to the HSV-1 ICP8 gene between 0.38 and 0.41 map units (m.u.), and BHV-2 nucleotide sequences homologous to the HSV-1 VP5 gene between 0.24 and 0.27 m.u. In addition, BHV-2 nucleotide sequences homologous to HSV-1 genes for TK, gB and gD were found to lie on both sides of restriction endonuclease cleavage sites at 0.30, 0.35, and 0.94 m.u., respectively.

The contribution of cysteine residues to antigenicity and extent of processing of herpes simplex virus type 1 glycoprotein D

Glycoprotein D (gD) is an envelope component of herpes simplex virus types 1 (gD-1) and 2 (gD-2). The gD-1 polypeptide contains seven cysteine residues among its 369 amino acids; six are located on the N-terminal or luminal portion of the glycoprotein, and a seventh is located in the transmembrane region. Previous studies used a panel of monoclonal antibodies (MAbs) to define gD epitopes as continuous or discontinuous. Purified gD, denatured by reduction and alkylation, loses discontinuous epitopes, whereas continuous epitopes are retained. The contribution of disulfide bonds to maintenance of discontinuous epitopes is, therefore, significant. In the present study, our objective was to determine the contribution of individual cysteine residues to folding of gD-1 into its native conformation. Site-directed oligonucleotide mutagenesis was used to create seven mutants, each with a serine residue replacing a cysteine. The mutated genes were cloned into a eucaryotic expression vector and transfected into COS-1 cells, and the proteins were separated by nondenaturing polyacrylamide gel electrophoresis, followed by immunoblotting. Replacement of cysteine 7 (residue 333) had only a minimal effect on the antigenic properties of gD-1. In contrast, replacement of any one of the other six cysteine residues resulted in either a major reduction or a complete loss of binding of those MAbs that recognize discontinuous epitopes, with no effect on the binding of MAbs which recognize continuous epitopes. These mutations also had profound effects on the extent of oligosaccharide processing of gD-1. This was determined by digestion of the expressed proteins with various endoglycosidases, followed by electrophoresis and Western blotting (immunoblotting) to observe any mobility changes. Three mutant gD proteins which did not express discontinuous epitopes contained only high-mannose-type oligosaccharides, suggesting that processing had not proceeded beyond the precursor stage. Two mutant forms of gD exhibited reduced binding of MAbs to discontinuous epitopes. A small proportion of the molecules which accumulated at 48 h posttransfection contained complex oligosaccharides. One mutant exhibited reduced binding of MAbs to discontinuous epitopes, but was present at 48 h posttransfection only in the precursor form. The cysteine 7 mutant was processed to the same extent as wild-type gD. We conclude that the first six cysteine residues are critical to the correct folding, antigenic structure, and processing of gD-1, and we speculate that they form three disulfide-bonded pairs.

Herpes simplex virus immunoglobulin G Fc receptor activity depends on a complex of two viral glycoproteins, gE and gI

Evidence was recently presented that herpes simplex virus type 1 (HSV-1) immunoglobulin G (IgG) Fc receptors are composed of a complex containing a previously described glycoprotein, gE, and a novel virus-induced polypeptide, provisionally named g70 (D. C. Johnson and V. Feenstra, J. Virol. 61:2208-2216, 1987). Using a monoclonal antibody designated 3104, which recognizes g70, in conjunction with antipeptide sera and virus mutants unable to express g70 or gE, we have mapped the gene encoding g70 to the US7 open reading frame of HSV-1 adjacent to the gE gene. Therefore, g70 appears to be identical to a recently described polypeptide which was named gI (R. Longnecker, S. Chatterjee, R. J. Whitley, and B. Roizman, Proc. Natl. Acad. Sci. USA 84:147-151, 1987). Under mildly denaturing conditions, monoclonal antibody 3104 precipitated both gI and gE from extracts of HSV-1-infected cells. In addition, rabbit IgG precipitated the gE-gI complex from extracts of cells transfected with a fragment of HSV-1 DNA containing the gI, gE, and US9 genes. Cells infected with mutant viruses which were unable to express gE or gI did not bind radiolabeled IgG; however, cells coinfected with two viruses, one unable to express gE and the other unable to express gI, bound levels of IgG approaching those observed with wild-type viruses. These results further support the hypothesis that gE and gI form a complex which binds IgG by the Fc domain and that neither polypeptide alone can bind IgG.

Regulation of glycoprotein D synthesis: does alpha 4, the major regulatory protein of herpes simplex virus 1, regulate late genes both positively and negatively?

Earlier studies have described the alpha 4/c113 baby hamster kidney cell line which constitutively expresses the alpha 4 protein, the major regulatory protein of herpes simplex virus 1 (HSV-1). Introduction of the HSV-1 glycoprotein B (gB) gene, regulated as a gamma 1 gene, into these cells yielded a cell line which constitutively expressed both the alpha 4 and gamma 1 gB genes. The expression of the gB gene was dependent on the presence of functional alpha 4 protein. In this article we report that we introduced into the alpha 4/c113 and into the parental BHK cells, the HSV-1 BamHI J fragment, which encodes the domains of four genes, including those of glycoproteins D, G, and I (gD, gG, and gI), and most of the coding sequences of the glycoprotein E (gE) gene. In contrast to the earlier studies, we obtained significant constitutive expression of gD (also a gamma 1 gene) in a cell line (BJ) derived from parental BHK cells, but not in a cell line (alpha 4/BJ) which expresses functional alpha 4 protein. RNA homologous to the gD gene was present in significant amounts in the BJ cell line; smaller amounts of this RNA were detected in the alpha 4/BJ cell line. RNA homologous to gE, presumed to be polyadenylated from signals in the vector sequences, was present in the BJ cells but not in the alpha 4/BJ cells. The expression of the HSV-1 gD and gE genes was readily induced in the alpha 4/BJ cells by superinfection with HSV-2. The BJ cell line was, in contrast, resistant to expression of HSV-1 and HSV-2 genes. The BamHI J DNA fragment copy number was approximately 1 per BJ cell genome equivalent and 30 to 50 per alpha 4/BJ cell genome equivalent. We conclude that (i) the genes specifying gD and gB belong to different viral regulatory gene subsets, (ii) the gD gene is subject to both positive and negative regulation, (iii) both gD and gE mRNAs are subject to translational controls although they may be different, and (iv) the absence of expression of gD in the alpha 4/BJ cells reflects the expression of the alpha 4 protein in these cells.

Varicella-zoster virus gpI and herpes simplex virus gE: phosphorylation and Fc binding

gpI, the predominant varicella-zoster virus (VZV) envelope glycoprotein, was shown to be phosphorylated exclusively on serine and threonine residues, and phosphorylated gpI was detected in isolated virions. In cells infected with herpes simplex virus type 1 (HSV-1), a related neurotropic alpha-herpesvirus, HSV gE, the homolog to VZV gpI, and HSV gB, the homolog to VZV gpII, were also phosphorylated. The phosphate on gB and gE was alkali labile and resistant to endo H, suggesting linkage to serine and/or threonine. Although VZV gpI and HSV gE share sequence homology and similar post-translational modifications, no Fc-binding activity similar to that associated with gE was detected for gpI or any of the VZV glycoproteins.

The pseudorabies virus gII gene is closely related to the gB glycoprotein gene of herpes simplex virus

We have looked for conserved DNA sequences between four herpes simplex virus type 1 (HSV-1) glycoprotein genes encoding gB, gC, gD, and gE and pseudorabies virus (PRV) DNA, HSV-1 DNA fragments representing these four glycoprotein-coding sequences were hybridized to restriction enzyme fragments of PRV DNA by the Southern blot procedure. Specific hybridization was observed only when HSV-1 gB DNA was used as probe. This region of hybridization was localized to a 5.2-kilobase (kb) region mapping at approximately 0.15 map units on the PRV genome. Northern blot (RNA blot) analysis, with a 1.2-kb probe derived from this segment, revealed a predominant hybridizing RNA species of approximately 3 kb in PRV-infected PK15 cells. DNA sequence analysis of the region corresponding to this RNA revealed a single large open reading frame with significant nucleotide homology with the gB gene of HSV-1 KOS 321. In addition, the beginning of the sequenced PRV region also contained the end of an open reading frame with amino acid homology to HSV-1 ICP 18.5, a protein that may be involved in viral glycoprotein transport. This sequence partially overlaps the PRV gB homolog coding sequence. We have shown that the PRV gene with homology to HSV-1 gB encoded the gII glycoprotein gene by expressing a 765-base-pair segment of the PRV open reading frame in Escherichia coli as a protein fused to beta-galactosidase. Antiserum, raised in rabbits, against this fusion protein immunoprecipitated a specific family of PRV glycoproteins of apparent molecular mass 110, 68, and 55 kilodaltons that have been identified as the gII family of glycoproteins. Analysis of the predicted amino acid sequence indicated that the PRV gII protein shares 50% amino acid homology with the aligned HSV-1 gB protein. All 10 cysteine residues located outside of the signal sequence, as well as 4 of 6 potential N-linked glycosylation sites, were conserved between the two proteins. The primary protein sequence for HSV-1 gB regions known to be involved in the rate of virus entry into the cells and cell-cell fusion, as well as regions known to be associated with monoclonal antibody resistance, were highly homologous with the PRV protein sequence. Furthermore, monospecific antibody made against PRV gII immunoprecipitated HSV-1 gB from infected cells. Taken together, these findings suggest significant conservation of structure and function between the two proteins and may indicate a common evolutionary history.

Use of lambda gt11 and monoclonal antibodies to map the genes for the six major glycoproteins of equine herpesvirus 1

To localize the genes for the major glycoproteins of equine herpesvirus 1 (EHV-1), a library of the EHV-1 genome was constructed in the lambda gt11 expression vector. Recombinant bacteriophage expressing EHV-1 glycoprotein epitopes as fusion products with beta-galactosidase were detected by immunoscreening with monoclonal antibodies specific for each of six EHV-1 glycoproteins. Seventy-four recombinant lambda gt11 clones reactive with EHV-1 monoclonal antibodies were detected among 4 X 10(5) phage screened. Phage expressing determinants on each of the six EHV-1 glycoproteins were represented in the library. Herpesviral DNA sequences contained in lambda gt11 recombinants expressing epitopes of EHV-1 glycoproteins were used as hybridization probes for mapping insert sequences on the viral genome. Genes for five EHV-1 glycoproteins (gp2, gp10, gp13, gp14, and gp21/22a) mapped to the genome L component; only one EHV-1 glycoprotein (gp17/18) was expressed from the unique S region of the genome where genes of several major glycoproteins of other herpesviruses have been located. Two glycoproteins of EHV-1, gp13 and gp14, mapped to positions colinear with genes of major glycoproteins identified in several other alphaherpesviruses (gC- and gB-like glycoproteins, respectively). The genomic locations of other EHV-1 glycoproteins indicated the existence of major glycoproteins of EHV-1 (gp2, gp10, and gp21/22a) for which no genetic homologs have yet been detected in other herpesviruses. The results confirm the general utility of the lambda gt11 expression system for localizing herpesvirus genes and suggest that the genomic positioning of several high-abundance glycoproteins of EHV-1 may be different from that of the prototype alphaherpesvirus, herpes simplex virus.

Identification of a novel herpes simplex virus type 1-induced glycoprotein which complexes with gE and binds immunoglobulin

We detected a glycoprotein on the surface of cells infected with herpes simplex virus type 1 (HSV-1) which, in conjunction with gE, binds immunoglobulin G (IgG). The novel glycoprotein, which has an apparent molecular mass of 70 kilodaltons and was provisionally named g70, was first detected in extracts of HSV-1-infected cells labeled by lactoperoxidase-catalyzed iodination and precipitated with rabbit sera or IgG and protein A-Sepharose. In subsequent experiments, g70 and gE were coprecipitated from extracts of HSV-1-infected cells labeled with [35S]methionine, [35S]cysteine, or 14C-amino acids. We were unable to precipitate a polypeptide analogous to g70 or gE from extracts of HSV-2-infected cells with rabbit IgG and protein A-Sepharose. Partial proteolytic peptide analysis indicated that g70 is structurally distinct from gE and gI). In addition, g70 was electrophoretically distinct from the HSV-1 Us4 glycoprotein gG. HSV-1 gE, expressed in mouse cells transfected with the gE gene, was not precipitated with rabbit IgG, nor could these cells bind radiolabeled IgG, suggesting that gE alone cannot act as an IgG (Fc) receptor. This result, coupled with the findings that gE and g70 are coprecipitated with IgG and with an anti-gE monoclonal antibody, suggests that gE and g70 form a complex which binds IgG. The electrophoretic mobilities of g70 molecules induced by different strains of HSV-1 differed markedly, arguing that g70 is encoded by the virus and is not a cellular protein induced by virus infection.

Identification of a herpes simplex virus 1 glycoprotein gene within a gene cluster dispensable for growth in cell culture

The genome of herpes simplex virus 1 consists of two components, L and S, each containing unique sequences flanked by inverted repeats. Current and earlier studies have shown that 11 of the 12 open reading frames contained in the unique sequences of the S component can be deleted and are dispensable for growth in cell culture. Analyses of one recombinant virus containing a deletion in the open reading frame US7 permitted the identification of a monoclonal antibody specific for the product of this gene. The protein encoded by this gene has a predicted translated molecular weight of 41,366 and an apparent molecular weight of approximately 65,000 in denaturing polyacrylamide gels. The electrophoretic mobility of the protein synthesized by cells in the presence of inhibitory concentrations of tunicamycin is faster than that of the protein accumulating in lysates of untreated infected cells. We conclude that the product of US7 is glycoprotein subject to N-linked glycosylation, and we have designated it glycoprotein I. These studies indicate that the unique sequences of the S component encode four glycoproteins (G, D, I, and E) of which at least three (G, I, and E) are dispensable for growth in continuous lines of primate cells.

Rapid identification of nonessential genes of herpes simplex virus type 1 by Tn5 mutagenesis

The large genome of herpes simplex virus type of (HSV-1) encodes at least 80 polypeptides, the majority of which have no recognized function. A subgroup of these gene products appears to be nonessential for virus replication in cell culture, but contributes to the complex life cycle of the virus in the host. To identify such functions, a simple insertional mutagenesis method has been used for selective inactivation of individual HSV-1 genes. The bacterial transposon Tn5 was allowed to insert randomly into cloned restriction fragments representing the entire short unique (US) region of the HSV-1 genome. Of the 12 open reading frames that were mutagenized with Tn5, mutant derivatives of US2, US4, and US5 were recombined into the virus. These three genes proved to be nonessential for HSV-1 replication in Vero (African Green monkey kidney) cells and the US4 gene appeared to be involved in viral pathogenesis in the central nervous system of mice. This rapid mutagenesis procedure should prove useful in exploring the entire HSV-1 genome as well as the genomes of other complex animal viruses.

Herpes simplex virus type 1 glycoprotein E is not indispensable for viral infectivity

A mutant of the herpes simplex virus type 1 Angelotti was isolated in which 87% of the coding region of glycoprotein E (gE) was deleted and replaced by a functional neomycin resistance gene of the Tn5 transposon. The mutant was characterized by restriction enzyme analyses and Southern blotting. Western blotting of proteins and immunofluorescence assays revealed that gE was completely absent and that the Fc receptor was not expressed in cells infected with the mutant. The fact that this mutant was viable and that it replicated to a slightly lower titer than did the wild-type virus suggests that the presence of gE is not a prerequisite of viral infectivity in tissue culture.

Localization of discontinuous epitopes of herpes simplex virus glycoprotein D: use of a nondenaturing ("native" gel) system of polyacrylamide gel electrophoresis coupled with Western blotting

Previously, a panel of monoclonal antibodies (MCAb) was used to define specific epitopes of herpes simplex virus glycoprotein D (gD) (R. J. Eisenberg et al., J. Virol. 53:634-644, 1985). Three groups of antibodies recognized continuous epitopes; group VII reacted with residues 11 to 19 of the mature protein (residues 36 to 44 of the predicted sequence), group II reacted with residues 272 to 279, and group V reacted with residues 340 to 356. Four additional antibody groups recognized discontinuous epitopes of gD, since their reactivity was lost when the glycoprotein was denatured by reduction and alkylation. Our goal in this study was to localize more precisely the discontinuous epitopes of gD. Using a nondenaturing system of polyacrylamide gel electrophoresis ("native" gel electrophoresis) coupled to Western blotting, we analyzed the antigenic activity of truncated forms of gD. These fragments were generated either by recombinant DNA methods or by cleavage of purified native gD-1 (gD obtained from herpes simplex virus type 1) and gD-2 (gD obtained from herpes simplex virus type 2) with Staphylococcus aureus protease V8. Antibodies in groups III, IV, and VI recognized three truncated forms of gD-1 produced by recombinant DNA methods, residues 1 to 287, 1 to 275, and 1 to 233. Antibodies in group I recognized the two larger forms but did not react with the gD-1 fragment of residues 1 to 233. On the basis of these and previous results, we concluded that a protion of epitope I was located within residues 233 to 259 and that epitopes III, IV, and VI were upstream of residue 233. Antibodies to continuous epitopes identified protease V8 fragments of gD-1 and gD-2 that contained portions of either the amino or carboxy regions of the proteins. None of the V8 fragments, including a 34K polypeptide containing residues 227 to 369, reacted with group I antibodies. This result indicated that a second portion of epitope I was located upstream of residue 227. Two amino-terminal fragments of gD-1, 33K and 30K, reacted with group III, IV, and VI antibodies. A 33K fragment of gD-2 reacted with group III antibodies. Based on their size and reactivity with endo-beta-N-acetylglycosaminidase F, we hypothesized that the 33K and 30K molecules represented residues 1 to 226 and 1 to 182 of gD-1, respectively. These results suggest that epitopes III, IV, and VI are located within the first 182 residues of gD.(ABSTRACT TRUNCATED AT 400 WORDS)

The herpes simplex virus type 2 equivalent of the herpes simplex virus type 1 US7 gene and its flanking sequences

Nucleotide sequencing studies (D. J. McGeoch, A. Dolan, S. Donald, and F. Rixon, 1985, J. Mol. Biol. 181, 1-14) have indicated that herpes simplex virus type 1 (HSV-1) has a coding sequence, referred to as US7, between the genes for the glycoproteins D and E (gD and gE). Northern blot analysis and nucleotide sequencing have been carried out to show that the type 2 virus (HSV-2) has an equivalent to the US7 gene. A comparison with the HSV-1 sequence has revealed some surprising similarities and differences. At the nucleotide level, HSV-2 has inserted a large sequence into the gE promoter, retained a large palindrome present in the coding sequence but not some tandem repeats, and deleted a region beside those repeats. At the amino acid level, the putative transmembrane sequence has been remarkably well conserved, and hydrophobic moment analysis indicates that it could be interacting with polar species within the plane of the membrane. Immediately after the deletion in the HSV-2 sequence, there is an N-glycosylation signal, and HSV-2 has one more such signal than HSV-1. The longest conserved sequence at the nucleotide level codes for a region of polypeptide that is strongly predicted to fold into alpha-helix. Implications of these analyses to the structure and possible function of these molecules are discussed.

Generation of an inverting herpes simplex virus 1 mutant lacking the L-S junction a sequences, an origin of DNA synthesis, and several genes including those specifying glycoprotein E and the alpha 47 gene

The herpes simplex virus genome consists of two components, L and S, that invert relative to each other to yield four isomeric arrangements, prototype (P), inversion of the S component (Is), inversion of the L component (Il), and inversion of both components (Isl). Previous studies have shown that the 500-base-pair a sequences flanking the two components contain a cis-acting site for inversion. In an attempt to insert a third copy of the alpha 4 gene, the major regulatory gene mapping in the repeats flanking the S component, a fragment containing the alpha 4 gene and an origin of DNA synthesis, was recombined into the thymidine kinase gene mapping in the unique sequences of the L component. The resulting recombinants showed massive rearrangements and deletions mapping in the S component and in the junction between the L and S components. One recombinant (R7023) yielded two isomeric DNA arrangements, a major component consisting of Is and a minor component consisting of Isl. In these arrangements, the genome lacked the gene specifying glycoprotein E and all contiguous genes located between it and the alpha 0 gene in the inverted repeats of the L component. Among the deleted sequences were those encoding an origin of viral DNA synthesis, the alpha 47 gene, and the a sequences located at the junction between the L and S-components. The recombinant grew well in rabbit skin, 143TK-, and Vero cell lines. We conclude that the four unique genes deleted in R7023 are not essential for the growth of herpes simplex virus, at least in the cell lines tested, and that the b sequence of the inverted repeats of the L component also contains cis-acting sites for the inversion of herpes simplex virus DNA sequences.

Identification, properties, and gene location of a novel glycoprotein specified by herpes simplex virus 1

We report the identification of a novel herpes simplex virus 1 (HSV-1) glycoprotein reactive with type specific monoclonal antibody H1379. The monoclonal antibody reacted with two broad bands with apparent mol wt of 60K to 68K and 44K to 48K formed by infected cell lysates subjected to electrophoresis in denaturing polyacrylamide gels and electrically transferred to a nitrocellulose sheet. Early in infection the H1379 reactive protein was found in the faster migrating band. The rate of accumulation was highest late in infection and only the slower migrating form incorporates significant amounts of glucosamine. The epitopic site recognized by H1379 was not uniformly distributed among strains. Analyses of HSV-1 X HSV-2 recombinants with monoclonal antibodies to HSV-1 and HSV-2 glycoproteins mapping in the S component of the HSV genomes and marker transfer experiments indicated that the gene specifying the H1379 reactive protein maps within BamHI fragment J to the left of gD most probably within the open reading frame designated as US4 (D. J. McGeoch, A Dolan, S. Donald, and F. J. Rixon, 1985, J. Mol. Biol. 181, 1-13). The gene specifying a recently discovered HSV-2 glycoprotein designated as gG-2 (B. Roizman, B. Norrild, C. Chan, and L. Pereira, 1984, Virology 133, 242-247) maps in the corresponding domain of the HSV-2 genome and marker transfer experiments suggest that the H1379 reactive protein and gG-2 are collinear. We have therefore designated the novel HSV-1 glycoprotein as gG-1.

Identification of a new glycoprotein of herpes simplex virus type 1 and genetic mapping of the gene that codes for it

A type-specific monoclonal antibody, LP10, precipitated a glycoprotein with a molecular weight of approximately 59,000 from purified herpes simplex virus type 1. Although this glycoprotein was similar in size to glycoprotein D (gD), it was shown to be less abundant in both virions and infected cells, to migrate more rapidly in its precursor form, to incorporate glucosamine but not mannose, and to have a more stable precursor in tunicamycin-treated cells than the gD precursor (pgD). Immunoassays of cells infected with insertion recombinants and intertypic recombinants localized the gene coding for the target antigen of LP10 to the unique short (Us) region at map units 0.892 to 0.924 excluding gD. The target antigen of LP10 was then definitively mapped to the Us4 open reading frame by immunoprecipitation of a polypeptide synthesized by in vitro translation of a Us4-specific transcript prepared by using an SP6 cloning This newly identified glycoprotein product of the Us4 gene of herpes simplex virus type 1 is distinct from the previously identified gB1, gC1, gE1, and gH1.

Respiratory syncytial virus envelope glycoprotein (G) has a novel structure

Amino acid sequence of human respiratory syncytial virus envelope glycoprotein (G) was deduced from the DNA sequence of a recombinant plasmid and confirmed by limited amino acid microsequencing of purified 90K G protein. The calculated molecular mass of the protein encoded by the only long open reading frame of 298 amino acids was 32,588 daltons and was somewhat smaller than the 36K polypeptide translated in vitro from mRNA selected by this plasmid. Inspection of the sequence revealed a single hydrophobic domain of 23 amino acids capable of membrane insertion at 41 residues from the N-terminus. There was no N-terminal signal sequence and the hydrophilic N-terminal 20 residues probably represent the cytoplasmic tail of the protein. The N-terminally oriented membrane insertion was somewhat analogous to paramyxovirus hemagglutinin-neuraminidase (HN) and influenza neuraminidase (NA). The protein was moderately hydrophilic and rich in hydroxy-amino acids. It was both N- and O-glycosylated with the latter contributing significantly to the net molecular mass 90K.

Utilization of internal AUG codons for initiation of protein synthesis directed by mRNAs from normal and mutant genes encoding herpes simplex virus-specified thymidine kinase

Previous studies (H.S. Marsden, L. Haarr, and C.M. Preston, J. Virol. 46:434-445, 1983) have shown that at least three polypeptides, with molecular weights of 43,000, 39,000, and 38,000, are encoded by the herpes simplex virus type 1 (HSV-1) thymidine kinase (TK) gene. It has been suggested that the 39,000- and 38,000-molecular-weight polypeptides arise from preinitiation complexes bypassing the first and second AUG codons before commencement of translation since, according to previous work (M. Kozak, Nucleic Acids Res. 9:5233-5252, 1981), these codons are not of the most efficient structure for initiation. This possibility was investigated by using specific herpes simplex virus mutants with alterations in the TK gene. Mutant TK4 has an amber mutation between the first and second AUG codons, whereas mutant delta 1 has a deletion which removes the first AUG codon but leaves other AUG codons, as well as transcriptional promoter sequences, intact. Both mutants synthesized only the 39,000- and 38,000-molecular-weight polypeptides, and the amounts produced were normal in TK4-infected cells but increased in delta 1-infected cells. Furthermore, the levels of TK produced after infection with the mutant viruses correlated with the amounts of the 39,000- and 38,000-molecular-weight polypeptides synthesized. The 43,000-, 39,000-, and 38,000-molecular-weight polypeptides were shown to be related by their positive reaction with anti-TK serum in both immunoprecipitation and immunoblotting experiments. The production of the 39,000- and 38,000-molecular-weight polypeptides through bypassing of the first AUG codon was examined by hybrid arrest experiments with a DNA fragment complementary to only 50 bases at the 5' terminus of TK mRNA. This fragment arrested the synthesis of the 30,000- and 38,000-molecular-weight polypeptides when annealed to mRNA from wild-type HSV-1- or TK4-infected cells, showing that those polypeptides arise from an mRNA initiated upstream from the first AUG codon. mRNA from cells infected with mutant delta 1, which lacks DNA sequences upstream from the first AUG, was not affected by the 50-base-pair fragment. The data therefore confirm that three polypeptides encoded by the HSV-1 TK gene arise by differential use of in-phase AUG codons for the initiation of protein synthesis. This mechanism for the production of related but distinct polypeptides has not previously been demonstrated in a eucaryotic system, and the implications for the regulation of TK enzyme activities are discussed.

Intracellular transport of herpes simplex virus gD occurs more rapidly in uninfected cells than in infected cells

A mouse L cell line which expresses the herpex simplex virus type 1 immediate-early polypeptides ICP4 and ICP47 was cotransfected with a cloned copy of the BglII L fragment of herpes simplex virus type 2, which includes the gene for gD, and the plasmid pSV2neo, which contains the aminoglycosyl 3'-phosphotransferase (agpt) gene conferring resistance to the antibiotic G418. A G418-resistant transformed cell line was isolated which expressed herpes simplex virus type 2 gD at higher levels than were found in infected cells. The intracellular transport and processing of gD was compared in transformed and infected cells. In the transformed Z4/6 cells gD was rapidly processed and transported to the cell surface; in contrast, the processing and cell surface appearance of gD in infected parental Z4 cells occurred at a much slower rate, and gD accumulated in nuclear membrane to a greater extent. Thus, the movement of HSV-2 gD to the cell surface in infected cells is retarded as viral glycoproteins accumulate in the nuclear envelope, probably because they interact with other viral structural components.

Cells that constitutively express the herpes simplex virus immediate-early protein ICP4 allow efficient activation of viral delayed-early genes in trans

To study the role of herpes simplex virus type 1 immediate-early proteins in the transcriptional activation of herpes simplex virus genes, we isolated stably transformed cells expressing herpes simplex virus type 1 ICP4, an immediate-early protein known from previous studies to be necessary for delayed-early and late transcription. These cells efficiently expressed six delayed-early herpes simplex virus genes introduced by viral superinfection, in the absence of de novo viral protein synthesis. In contrast, the delayed-early gene encoding alkaline exonuclease and the late gene encoding the capsid protein VP5 were expressed at much lower levels. Expression of a second late gene, that for glycoprotein C, was undetectable under the same experimental conditions. These results suggest that many, but not all, delayed-early genes are efficiently activated by ICP4; in addition, they demonstrate that although the late gene for VP5 is detectably activated by ICP4, its full expression requires additional factors.

Detailed analysis of the mRNAs mapping in the short unique region of herpes simplex virus type 1

We have analysed the mRNAs which map within the short unique (US) region of the herpes simplex virus type 1 (HSV-1) genome. US has a total length of 12979 base pairs (1) and is extensively transcribed with approximately 94% of the total sequence present in cytoplasmic mRNAs and 79% of the total sequence considered to be protein coding. There are several examples of overlapping functions and multiple use of DNA sequence within this region. US contains 12 genes (1) which are expressed as 13 mRNAs. Two of these mRNAs are thought to arise from the same gene since they differ only slightly in the positions of their 5' ends and probably specify the same polypeptide. 11 of the 13 mRNAs are arranged into four nested families with unique 5' ends and common 3' co-termini. The other two mRNAs have unique 5' and 3' ends.

Localization of epitopes of herpes simplex virus type 1 glycoprotein D

We previously defined eight groups of monoclonal antibodies which react with distinct epitopes of herpes simplex virus glycoprotein D (gD). One of these, group VII antibody, was shown to react with a type-common continuous epitope within residues 11 to 19 of the mature glycoprotein (residues 36 to 44 of the predicted sequence of gD). In the current investigation, we have localized the sites of binding of two additional antibody groups which recognize continuous epitopes of gD. The use of truncated forms of gD as well as computer predictions of secondary structure and hydrophilicity were instrumental in locating these epitopes and choosing synthetic peptides to mimic their reactivity. Group II antibodies, which are type common, react with an epitope within residues 268 to 287 of the mature glycoprotein (residues 293 to 312 of the predicted sequence). Group V antibodies, which are gD-1 specific, react with an epitope within residues 340 to 356 of the mature protein (residues 365 to 381 of the predicted sequence). Four additional groups of monoclonal antibodies appear to react with discontinuous epitopes of gD-1, since the reactivity of these antibodies was lost when the glycoprotein was denatured by reduction and alkylation. Truncated forms of gD were used to localize these four epitopes to the first 260 amino acids of the mature protein. Competition experiments were used to assess the relative positions of binding of various pairs of monoclonal antibodies. In several cases, when one antibody was bound, there was no interference with the binding of an antibody from another group, indicating that the epitopes were distinct. However, in other cases, there was competition, indicating that these epitopes might share some common amino acids.

Sequence determination and genetic content of the short unique region in the genome of herpes simplex virus type 1

We have determined the complete DNA sequence of the short unique region in the genome of herpes simplex virus type 1, strain 17, and have interpreted it in terms of messenger RNAs and encoded proteins. The sequence contains variable regions whose length differs between DNA clones. The clones used for most of the analysis gave a short unique length of 12,979 base-pairs. We consider that this region contains 12 genes, which are expressed by mRNAs which have separate promoters, but may share 3'-termination sites, so that all but two mRNAs belong to one of four 3'-coterminal "families": 79% of the sequence is considered to be polypeptide coding. One pair of genes has an extensive out-of-frame overlap of coding sequences. The proteins encoded in the short unique region include two immediate-early species, two virion surface glycoproteins, and a DNA-binding species. Six of the genes have little or no previous characterization. From the nature of the amino acid sequences predicted for their encoded proteins, we deduce that several of these proteins may be membrane-associated.

Use of a bacterial expression vector to map the varicella-zoster virus major glycoprotein gene, gC

The genome of varicella-zoster virus (VZV) encodes at least three major glycoprotein genes. Among viral gene products, the gC gene products are the most abundant glycoproteins and induce a substantial humoral immune response (Keller et al., J. Virol. 52:293-297, 1984). We utilized two independent approaches to map the gC gene. Small fragments of randomly digested VZV DNA were inserted into a bacterial expression vector. Bacterial colonies transformed by this vector library were screened serologically for antigen expression with monoclonal antibodies to gC. Hybridization of the plasmid DNA from a gC antigen-positive clone revealed homology to the 3' end of the VZV Us segment. In addition, mRNA from VZV-infected cells was hybrid selected by a set of VZV DNA recombinant plasmids and translated in vitro, and polypeptide products were immunoprecipitated by convalescent zoster serum or by monoclonal antibodies to gC. This analysis revealed that the mRNA encoding a 70,000-dalton polypeptide precipitable by anti-gC antibodies mapped to the HindIII C fragment, which circumscribes the entire Us region. We conclude that the VZV gC glycoprotein gene maps to the 3' end of the Us region and is expressed as a 70,000-dalton primary translational product. These results are consistent with the recently reported DNA sequence of Us (A.J. Davison, EMBO J. 2:2203-2209, 1983). Furthermore, glycosylation appears not to be required for a predominant portion of the antigenicity of gC glycoproteins. We also report the tentative map assignments for eight other VZV primary translational products.

Mapping of the structural gene of pseudorabies virus glycoprotein A and identification of two non-glycosylated precursor polypeptides

Cell-free translation of pseudorabies virus RNA isolated during the late phase of the infectious cycle yielded a variety of polypeptides. A monoclonal antibody directed against one of the major viral glycoproteins, gA, immunoprecipitated two polypeptides ranging in molecular weight from 78K to 83K. To localize the structural gene for gA, we used cloned BamHI fragments of the viral DNA to select specific mRNA species and immunoprecipitated their in vitro translation products with the anti-gA monoclonal antibody. This allowed us to map the genomic region encoding the mRNA for the gA within the short unique region of the viral genome on BamHI fragments 7 and 12. Additional polypeptides encoded by this region were characterized by their electrophoretic mobility. In three virus strains tested a similar, but strain-specific, pattern of the two gA precursors was found which was not dependent on the host cell or the state of infection after reaching the late phase.

Demonstration of three major species of pseudorabies virus glycoproteins and identification of a disulfide-linked glycoprotein complex

The glycoproteins of pseudorabies virus (PRV) Phylaxia were characterized with monoclonal antibodies as specific reagents. Three major structural glycoproteins with molecular weights of 155,000 (155K) (gC), 122K (gA), and 90K (gB) could be identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing conditions. We investigated the processing of glycoproteins gA, gB, and gC by in vitro translation, pulse-chase experiments, and in the presence of the ionophore monensin which inhibits glycosylation. gA and gB were found to compose a single polypeptide, whereas gC was found to be a disulfide-linked glycoprotein complex. Immunoprecipitates formed with the aid of anti-gC monoclonal antibodies gave rise to three glycoprotein bands (gC0 [120K], gC1 [67K], and gC2 [58K]) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions. Limited proteolysis of gC0, gC1, and gC2 resulted in peptide maps of gC0 related to those of both gC1 and gC2. No common peptide bands between gC1 and gC2, however, were seen. We suggest that (i) gC1 and gC2 arise by proteolytic cleavage from the same precursor molecule and stay joined via disulfide bridges and (ii) gC0 is an uncleaved precursor.

Expression of Herpes simplex virus type 1 glycoprotein C antigens in Escherichia coli

DNA fragments encoding structural information of the Herpes simplex virus type 1 (HSV-1) glycoprotein C (gC) gene were cloned into pUC plasmids [Vieira and Messing, Gene 19 (1982) 259-268]. None of the hybrid plasmids were able to direct the synthesis of significant amounts of gC related peptides. Several of the plasmid-bearing strains, however, exhibited inhibition characteristics which can be correlated with the presence on the plasmid of specific gC gene sequences. After insertion of gC DNA fragments into expression vector pMF2 between phage lambda repressor gene cI and lacZ, significant amounts of cI::gC::beta-galactosidase fusion proteins are synthesized. These tripartite fusion proteins are immunologically reactive with anti-HSV-1 antisera. The expression system based on pMF2 can be generally used to identify and express foreign antigens in Escherichia coli.

Molecular basis of the glycoprotein-C-negative phenotype of herpes simplex virus type 1 macroplaque strain

The basis for the inability of the macroplaque (MP) strain of herpes simplex virus type 1 to express mature glycoprotein C (gC) was examined. RNA transfer (Northern) blot analysis with hybridization probes from the region of the herpes simplex virus type 1 DNA known to encode the gC gene indicated that gC mRNA was produced in MP-infected HeLa cells at levels relative to other mRNAs comparable with that seen in KOS-infected cells. Comparative nucleotide sequence analysis of the gC gene from the MP and KOS strains, coupled with the results of recently reported marker rescue experiments, indicates that the inability of MP to produce gC is due to a frameshift mutation in the gC-coding sequence. Because two different (out-of-phase) open reading frames overlap the gC-coding sequence in the region of the mutation, MP mRNA can encode two gC-related polypeptides. Two polypeptides of the predicted size and precipitable by anti-gC antibodies were produced by in vitro translation of MP mRNA. These polypeptides have not been detected in extracts from infected cells with the same antibodies. Comparative nucleotide sequence analyses led to several corrections in the published sequence for the gC gene and the 17,800-molecular-weight polypeptide gene just to the right in KOS DNA. These relatively minor effects on the predicted amino code sequence of gC are tabulated.

Evidence for translational regulation of herpes simplex virus type 1 gD expression

We compared the rates of synthesis of herpes simplex virus type 1 glycoproteins C and D and quantitated the accumulation of translatable mRNA for each glycoprotein at various times after infection. The rate of synthesis of gD increased sharply early in the infection, peaked by 4 to 6 h after infection, and declined late in the infection. In contrast, the rate of synthesis of gC increased steadily until at least 15 h after infection. The levels of mRNA for both of these glycoproteins, as detected by hybridization and by translation in vitro, continued to increase until at least 15 or 16 h after infection. Synthesis of both gC and gD and their respective mRNAs was found to be sensitive to inhibition of viral DNA replication with phosphonoacetic acid. The finding that reduced amounts of gD were synthesized late in the replicative cycle, whereas gD mRNA continued to accumulate in the cytoplasm, argues that the synthesis of gD is regulated, in part, at the level of translation.

Isolation, characterization, and physical mapping of a pseudorabies virus mutant containing antigenically altered gp50

A pseudorabies virus variant ( mar197 -1) containing a mutation in a viral glycoprotein with a molecular weight of 50,000 ( gp50 ) was isolated by selecting for resistance to a neurtralizing monoclonal antibody ( MCA50 -1) directed against gp50 . This mutant was completely resistant to neutralization with MCA50 -1 in the presence or absence of complement, and was therefore defined as a mar (monoclonal-antibody-resistant) mutant. The mutation did not affect neutralization with polyvalent immune serum. The mar197 -1 mutant synthesized and processed gp50 normally, but the mutation prevented the binding and immunoprecipitation of gp50 by MCA50 -1. Thus, the mutation was within the structural portion of the gp50 gene affecting the epitope of the monoclonal antibody. The mutation was mapped by marker rescue with cloned pseudorabies restriction enzyme fragments to the short region of the pseudorabies genome between 0.813 and 0.832 map units. This is equivalent to a 2.1-kilobase-pair region.