Isolation of a nucleocapsid polypeptide of herpes simplex virus types 1 and 2 possessing immunologically type-specific and cross-reactive determinants

Characterization of polyclonal antibodies to Herpes Simplex Virus types 1 and 2

Infections with herpes simplex virus (HSV) types 1 and 2 have been linked to oral, facial, genital lesions, as well as some visceral organ changes in patients under immunosuppressed conditions. Immunohistochemistry (IHC) with HSV antibodies is used for identification of the viruses in tissue samples. In this study, two polyclonal antibodies, prepared separately with HSV-1 and HSV-2 immunogens, were characterized in comparison to a monoclonal antibody to HSV-1 (10A3). The polyclonal anti-HSV-1 and monoclonal antibody 10A3 were shown to be reactive to viral proteins of both HSV-1 and HSV-2 on Western blots, while the polyclonal anti-HSV-2 was reactive to HSV-2 proteins, but not to those of HSV-1. Cross-reactivity was not observed to proteins of six other frequently encountered herpes viruses. IHC characterization was performed on 29 cases of HSV-infected tissue samples, 61 samples infected with other herpes viruses and 35 samples without known infection. By IHC, the polyclonal anti-HSV-1 and a monoclonal antibody 10A3 exhibited a signal, mainly in a nuclear pattern, in all of the HSV-infected samples and not in other tissue types. A positive signal, mainly in the cytoplasm, was identified with the polyclonal anti-HSV-2 in 21 of the 29 HSV-infected samples. Genotyping analysis was successful in 14 of the HSV-infected samples, with IHC HSV-2 positivity correlative to the HSV-2 genotype. The results demonstrate that these antibodies are useful tools for identification of HSV-1 and HSV-2, and their combinatorial application may help to distinguish between these two types of infection.

The Herpesvirus capsid surface protein, VP26, and the majority of the tegument proteins are dispensable for capsid transport toward the nucleus

Upon entering a cell, alphaherpesvirus capsids are transported toward the minus ends of microtubules and ultimately deposit virus DNA within the host nucleus. The virus proteins that mediate this centripetal transport are unknown but are expected to be either viral tegument proteins, which are a group of capsid-associated proteins, or a surface component of the capsid itself. Starting with derivatives of pseudorabies virus that encode a fluorescent protein fused to a structural component of the virus, we have made a collection of 12 mutant viruses that lack either the VP26 capsid protein or an individual tegument protein. Using live-cell fluorescence microscopy, we tracked individual virus particles in axons following infection of primary sensory neurons. Quantitative analysis of the VP26-null virus indicates that this protein plays no observable role in capsid transport. Furthermore, viruses lacking tegument proteins that are nonessential for virus propagation in cell culture were also competent for axonal transport. These results indicate that a protein essential for viral propagation mediates transport of the capsid to the nucleus.

Assembly of Marek's disease virus (MDV) capsids using recombinant baculoviruses expressing MDV capsid proteins

The genes UL18, UL19, UL26, UL26.5, UL35 and UL38 of Marek's disease virus 1 (MDV-1) strain RB1B, encoding the homologues of herpes simplex virus type 1 (HSV-1) capsid proteins VP23, VP5, VP21-VP24, preVP22a, VP26 and VP19C, were identified and sequenced. Recombinant baculoviruses were used to express the six capsid genes in insect cells. Coexpression of the six genes or of UL18, UL19, UL26.5 and UL38 in insect cells resulted in the formation of capsids with a large core. In addition, electron microscopy of thin sections clearly revealed the presence of large numbers of small spherical particles. Experimental coinfection demonstrated that these small particles were associated with production of the preVP22a protein.

Mutations in the N-terminus of VP5 alter its interaction with the scaffold proteins of herpes simplex virus type 1

During the assembly process of herpes simplex virus type 1 capsids, there is an essential interaction between the C-terminal tail of the scaffold proteins (22a and 21) and the major capsid protein (VP5). Recent studies of spontaneous revertant viruses that overcome a blocked maturation cleavage site of the scaffold proteins have shown that the N-terminus of VP5 is important for this interaction. One of the revertant viruses, PR7, encodes a second-site mutation at residue 69 of VP5 which unlike wild-type VP5 fails to interact with 22a and thus gives white colonies in the yeast two-hybrid assay. In the present study a small DNA fragment, encoding residues 1 to 85 of wild-type and PR7 VP5, was mutagenized using error-prone PCR. Mutagenized DNA was used in the yeast two-hybrid assay to identify mutations in wild-type VP5 that resulted in loss of 22a binding (white colonies), or in PR7 VP5 that resulted in a gain of function (blue colonies). For the loss of function experiments, using KOS VP5, a row of eight thymidine nucleotides (codons 37-40) resulted in many frameshift mutations, which led us to terminate the study without reaching a statistically significant result. For the PR7 experiment, 30 clones were identified that had single amino acid substitutions, and these mutations were localized to amino acids 27-45 and 63-84 of VP5. The most frequent mutation was a reversion back to wild-type. The next most frequent were E28K and N63S, and these gave the highest beta-galactosidase enzyme activities (indicative of PR7VP5-22a interaction), 30 and 20% of wild-type, respectively. When E28K and N63S were transferred into the wild-type VP5 background, that is, in the absence of the PR7 mutation, they gave rise to different phenotypes. The E28K mutation lost its ability to interact with the scaffold proteins as judged by this assay. Therefore, it may be acting as a compensatory mutation whose phenotype is only expressed in the presence of the original PR7 mutation. However, the N63S mutation in the wild-type VP5 background increased the interaction, as judged by the beta-galactosidase activity, by a factor of 9 relative to when the PR7 mutation was present. Even more surprising, in the absence of the PR7 mutation the enzyme activity was still greater, by a factor of 2, than that observed for wild-type VP5. This study provides further evidence that the N-terminus of VP5 is in intimate association with the C-terminus of the scaffold proteins.

Second-site mutations encoding residues 34 and 78 of the major capsid protein (VP5) of herpes simplex virus type 1 are important for overcoming a blocked maturation cleavage site of the capsid scaffold proteins

During assembly of the herpes simplex type 1 capsid, the major capsid protein VP5 interacts with the C-terminal residues of the scaffold proteins encoded by UL26 and UL26.5. Subsequent to capsid assembly the scaffold proteins are cleaved at the maturation site by a serine protease also encoded by UL26, thereby enabling the bulk of the scaffold proteins to be released from the capsid. Previously, a mutant virus (KUL26-610/611) was isolated in which this maturation cleavage site was blocked by replacing the Ala/Ser at the 610/611 cleavage site by Glu/Phe. This mutation was lethal and required a transformed cell line expressing wild-type UL26 gene products for growth. Although the mutation was lethal, spontaneous reversions occurred at a high frequency. Previously, a small number of revertants were isolated and all were found to have second-site mutations in VP5. The purpose of the present study was to do a comprehensive determination of the sites altered in VP5 by the second-site mutations. To do this, an additional 25 independent spontaneous revertants were characterized. Seven of the 25 arose by GC --> GT changes in codon 78, giving rise to an alanine to valine substitution. Four were the result of base changes at codon 34 but two different amino acids were produced as the changes were at different positions in the codon. Two mutations were detected at position 41 and mutations that occurred once were found at codons 69 and 80. Thus, 15 of the 25 second-site mutants were localized to codons 34 to 80 of VP5, which contains 1374 amino acids. The remaining 10 revertants had codon changes at nine different sites, of which the most N-terminal was altered at codon 187 and the most C-terminal at codon 1317. As noted in the much smaller study a preponderance of the second-site mutants in VP5 were altered in codons at the extreme N-terminus of VP5. It is especially noteworthy that 11 out of 25 of the mutations occurred at codons 34 and 78. As expected, all of the revertants isolated were shown to retain the original KUL26-610/611 mutation, and the scaffold proteins remain uncleaved. All showed decreased retention of VP24 in the B capsids compared to the wild-type KOS, but more than the KUL26-610/611 parental virus. The revertants all had decreased growth rates of 2 to 18% compared to that of KOS and showed varying degrees of sensitivity when grown at 39.5 degrees C. The mutations in VP5 of three of the previously isolated viruses (PR5, PR6, and PR7) were transferred into a wild-type background, i.e., a virus encoding wild-type UL26 and UL26.5 gene products. All replicated in nonpermissive (Vero) cells and cleaved scaffold proteins. PR5 and PR6 in the wild-type background gave wild-type burst sizes and gave C-capsids that retained VP24 at approximately wild-type levels. The third revertant, PR7, in the wild-type background showed only a twofold increase of burst size (to 20% of wild-type) and the capsids showed little or no increase of VP24 retention. Therefore, the second-site mutations of PR7 (R69C) by itself had a negative effect on virus replication. By contrast the temperature sensitivity of PR6 and PR7 remained unchanged in the wild-type background. Thus the temperature sensitivity of PR6 and PR7 resides in VP5 independently of the mutation in the UL26 cleavage site.

Second site mutations in the N-terminus of the major capsid protein (VP5) overcome a block at the maturation cleavage site of the capsid scaffold proteins of herpes simplex virus type 1

VP5, the major capsid protein of herpes simplex virus type 1 (HSV-1), interacts with the C-terminal residues of the scaffold molecules encoded by the overlapping UL26 and UL26.5 open reading frames. Scaffold molecules are cleaved by a UL26 encoded protease (VP24) as part of the normal capsid assembly process. In this study, residues of VP5 have been identified that alter its interaction with the C-terminal residues of the scaffold proteins. A previously isolated virus (KUL26-610/611) was used that encoded a lethal mutation in the UL26 and UL26.5 open reading frames and required a transformed cell line that expresses these proteins for virus growth. The scaffold maturation cleavage site between amino acids 610 and 611 was blocked by changing Ala-Ser to Glu-Phe, which generated a new EcoRI restriction site. Revertant viruses, that formed small plaques on nontransformed cells, were detected at a frequency of 1:3800. Nine revertants were isolated, and all of them retained the EcoRI site and therefore were due to mutations at a second site. The second site mutations were extragenic. Using marker-transfer techniques, the mutation in one of the revertants was mapped to the 5' region of the gene encoding VP5. DNA sequence analysis was performed for the N-terminal 571 codons encoding VP5 for all of the revertant viruses. Six of the nine revertants showed a single base pair change that caused an amino acid substitution between residues 30 and 78 of VP5. Three of these were identical and changed Ala to Val at residue 78. The data provide a partial map of residues of VP5 that alter its interaction with scaffold proteins blocked at their normal cleavage site. The yeast two-hybrid system was used as a measure of the interaction between mutant VP5 and scaffold molecules and varied from 11% to nearly 100%, relative to wild-type VP5. One revertant gave no detectable interaction by this assay. The amount of UL26 encoded protease (VP24) in B capsids for KUL26-610/611 and for revertants was 7% and 25%, respectively, relative to the amount in capsids for wild-type virus. The lack of retention of the viral protease in the mutant virus and a fourfold increase for the revertants suggest an additional essential function for VP24 in capsid maturation, and a role in DNA packaging is indicated.

Incorporation of the green fluorescent protein into the herpes simplex virus type 1 capsid

The herpes simplex virus type 1 (HSV-1) UL35 open reading frame (ORF) encodes a 12-kDa capsid protein designated VP26. VP26 is located on the outer surface of the capsid specifically on the tips of the hexons that constitute the capsid shell. The bioluminescent jellyfish (Aequorea victoria) green fluorescent protein (GFP) was fused in frame with the UL35 ORF to generate a VP26-GFP fusion protein. This fusion protein was fluorescent and localized to distinct regions within the nuclei of transfected cells following infection with wild-type virus. The VP26-GFP marker was introduced into the HSV-1 (KOS) genome resulting in recombinant plaques that were fluorescent. A virus, designated K26GFP, was isolated and purified and was shown to grow as well as the wild-type virus in cell culture. An analysis of the intranuclear capsids formed in K26GFP-infected cells revealed that the fusion protein was incorporated into A, B, and C capsids. Furthermore, the fusion protein incorporated into the virion particle was fluorescent as judged by fluorescence-activated cell sorter (FACS) analysis of infected cells in the absence of de novo protein synthesis. Cells infected with K26GFP exhibited a punctate nuclear fluorescence at early times in the replication cycle. At later times during infection a generalized cytoplasmic and nuclear fluorescence, including fluorescence at the cell membranes, was observed, confirming visually that the fusion protein was incorporated into intranuclear capsids and mature virions.

Herpes simplex virus type 1 VP26 is not essential for replication in cell culture but influences production of infectious virus in the nervous system of infected mice

VP26 is the smallest capsid protein of herpes simplex virus type 1 and is encoded by the UL35 open reading frame. It resides on the outer capsid surface, interacting with VP5 in a one to one stoichiometry in the hexons that comprise capsids. A null mutation in the gene encoding VP26 was generated and transferred into the KOS genome. Recombinant viruses were isolated on Vero cells, which indicated that the absence of VP26 was not required for growth of the virus in cell culture. This was confirmed by the characterization of the VP26 null mutant, designated K delta 26Z. The yield of virus from K delta 26Z-infected Vero cells was decreased only twofold relative to wild-type-infected cells, as judged by the burst size. All three types of capsids (A, B, and C) were observed after sedimentation analysis of K delta 26Z-infected cell extracts. These capsids were similar in composition to wild-type capsids except for the absence of VP26. The mouse ocular model was used to determine if VP26 played a major role in vivo. The yield of the mutant virus relative to wild-type virus was decreased twofold in the eye; however, the mutant virus yields were decreased 30- to 100-fold in the trigeminal ganglia. Reactivation of the mutant virus as determined by cocultivation assays was also reduced. To determine the effect of VP26 on capsid translocation, the VP26 null mutation was transferred into a virus specifiying a thymidine kinase mutation that by itself is transported to the trigeminal ganglia but whose DNA is not replicated in the ganglia. Using quantitative PCR assays the number of viral genomes detected in the ganglia was similar in the presence or the absence of VP26. Therefore, VP26 does not appear to aid in the translocation of the virus capsid from the mouse eye to the trigeminal ganglia but is important for infectious virus production in the ganglia.

Capsids are formed in a mutant virus blocked at the maturation site of the UL26 and UL26.5 open reading frames of herpes simplex virus type 1 but are not formed in a null mutant of UL38 (VP19C)

Previously we reported that null mutant viruses of UL19 (VP5) or of UL18 (VP23), essential components of herpes simplex virus type 1 (HSV-1) capsid shells, do not form precursor capsid structures as judged by sedimentation and electron microscope analysis. A goal of the present experiments was to isolate a null mutant virus for the remaining essential component of capsid shells, VP19C, encoded by the UL38 open reading frame (ORF). Furthermore, we wished to determine if a virus altered in the UL26 maturation cleavage site at residues 610 and 611 produced a lethal phenotype. Therefore, we decided to isolate cell lines that encode and express multiple capsid genes. Several cell lines were isolated by transformation of Vero cells and one designated C32 expressed all of the essential capsid proteins. Using this cell line we isolated a null mutant virus in the UL38 ORF and a mutant virus that was altered at residues 610 and 611 of the UL26 and UL26.5 gene products. We found that the null mutant in VP19C did not form a detectable product as judged by sedimentation and electron microscope analyses following infection of nonpermissive cells. The mutant virus altered at the UL26 maturation site resulted in the accumulation of B capsids. Therefore, cleavage at this site was essential for the maturation of B capsids into C capsids. Interestingly, the absence of cleavage at the maturation site was required for the retention of VP24 in the capsid.

Hexon-only binding of VP26 reflects differences between the hexon and penton conformations of VP5, the major capsid protein of herpes simplex virus

VP26 is a 12-kDa capsid protein of herpes simplex virus 1. Although VP26 is dispensable for assembly, the native capsid (a T=16 icosahedron) contains 900 copies: six on each of the 150 hexons of VP5 (149 kDa) but none on the 12 VP5 pentons at its vertices. We have investigated this interaction by expressing VP26 in Escherichia coli and studying the properties of the purified protein in solution and its binding to capsids. Circular dichroism spectroscopy reveals that the conformation of purified VP26 consists mainly of beta-sheets (approximately 80%), with a small alpha-helical component (approximately 15%). Its state of association was determined by analytical ultracentrifugation to be a reversible monomer-dimer equilibrium, with a dissociation constant of approximately 2 x 10(-5) M. Bacterially expressed VP26 binds to capsids in the normal amount, as determined by quantitative sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Cryoelectron microscopy shows that the protein occupies its usual sites on hexons but does not bind to pentons, even when available in 100-fold molar excess. Quasi-equivalence requires that penton VP5 must differ in conformation from hexon VP5: our data show that in mature capsids, this difference is sufficiently pronounced to abrogate its ability to bind VP26.

Human cytomegalovirus capsid assembly protein precursor (pUL80.5) interacts with itself and with the major capsid protein (pUL86) through two different domains

We have used the yeast GAL4 two-hybrid system to examine interactions between the human cytomegalovirus (HCMV) major capsid protein (MCP, encoded by UL86) and the precursor assembly protein (pAP, encoded by UL80.5 and cleaved at its carboxyl end to yield AP) and found that (i) the pAP interacts with the MCP through residues located within the carboxy-terminal 21 amino acids of the pAP, called the carboxyl conserved domain (CCD); (ii) the pAP interacts with itself through a separate region, called the amino conserved domain (ACD), located between amino acids His34 and Arg52 near the amino end of the molecule; (iii) the simian CMV (SCMV) pAP and AP can interact with or replace their HCMV counterparts in these interactions, whereas the herpes simplex virus pAP and AP homologs cannot; and (iv) the HCMV and SCMV maturational proteinase precursors (ACpra, encoded by UL80a and APNG1, respectively) can interact with the pAP and MCP. The ACD and CCD amino acid sequences are highly conserved among members of the betaherpesvirus group and appear to have counterparts in the alpha- and gammaherpesvirus pAP homologs. Deleting the ACD from the HCMV pAP, or substituting Ala for a conserved Leu in the ACD, eliminated detectable pAP self-interaction and also substantially reduced MCP binding in the two-hybrid assay. This finding indicates that the pAP self-interaction influences the pAP-MCP interaction. Immunofluorescence studies corroborated the pAP-MCP interaction detected in the GAL4 two-hybrid experiments and showed that nuclear transport of the MCP was mediated by pAP but not AP. We conclude that the pAP interacts with the MCP, that this interaction is mediated by the CCD and is influenced by pAP self-interaction, and that one function of the pAP-MCP interaction may be to provide a controlled mechanism for transporting the MCP into the nucleus.

Two-dimensional gel analysis of [35S]methionine labelled and phosphorylated proteins present in virions and light particles of herpes simplex virus type 1, and detection of potentially new structural proteins

Cells infected with herpes simplex virus (HSV) synthesize both infectious viruses and non-infectious light particles (L-particles). The latter contain the envelope and tegument components of the virions, but lack virus capsid and DNA. Electrophoresis in SDS-polyacrylamide gels (SDS-PAGE) has been used extensively for analysis of structural proteins in virions and L-particles. Two-dimensional (2-D) gel electrophoresis, however has a markedly higher resolution, and in the present work we have used this technique to study both [35S]methionine labelled and phosphorylated structural proteins in virions and L-particles. Proteins were assigned to the tegument or the envelope by the analysis of L-particles. Localization of structural proteins was also determined by stepwise solubilization in the presence of the neutral detergent NP-40 and NaCl, and by isolation of capsids from nuclei of infected cells. Different steps in posttranslational modification can be detected by 2-D gel electrophoresis such that a single polypeptide may appear as several spots. This was most clearly observed for some of the HSV-encoded glycoproteins which were shown to exist in multiple forms in the virion. Some polypeptides apparently not identified previously were either capsid associated, or localized in the tegument or envelope. The degrees of phosphorylation in L-particles and virions are almost identical for some proteins, but markedly different for others. Thus, glycoprotein E of HSV-1 is for the first time shown to be phosphorylated, and most heavily so in virions. The IE VMW)110 protein represents a group of proteins which are more phosphorylated in L-particles than in virions. Attempts are made to correlate the proteins detected by 2-D analysis with those previously separated by SDS-PAGE.

Human cytomegalovirus (HCMV) smallest capsid protein identified as product of short open reading frame located between HCMV UL48 and UL49

The capsid of cytomegalovirus contains an abundant, low-molecular-weight protein whose coding sequence within the viral genome had not been identified. We have used a combination of biochemical and immunological techniques to demonstrate that this protein, called the smallest capsid protein in human cytomegalovirus, is encoded by a previously unidentified 225-bp open reading frame (ORF) located between ORFs UL48 and UL49. This short ORF, called UL48/49, is the positional homolog of herpes simplex virus ORF UL35 (encoding capsid protein VP26) and shows partial amino acid sequence identity to positional homologs in human herpes viruses 6 and 7.

Separate functional domains of the herpes simplex virus type 1 protease: evidence for cleavage inside capsids

The herpes simplex virus type 1 (HSV-1) protease (Pra) and related proteins are involved in the assembly of viral capsids and virion maturation. Pra is a serine protease, and the active-site residue has been mapped to amino acid (aa) 129 (Ser). This 635-aa protease, encoded by the UL26 gene, is autoproteolytically processed at two sites, the release (R) site between amino acid residues 247 and 248 and the maturation (M) site between residues 610 and 611. When the protease cleaves itself at both sites, it releases Nb, the catalytic domain (N0), and the C-terminal 25 aa. ICP35, a substrate of the HSV-1 protease, is the product of the UL26.5 gene. As it is translated from a Met codon within the UL26 gene, ICP35 cd are identical to the C-terminal 329-aa sequence of the protease and are trans cleaved at an identical C-terminal site to generate ICP35 e,f and a 25-aa peptide. Only fully processed Pra (N0 and Nb) and ICP35 (ICP35 e,f) are present in B capsids, which are believed to be precursors of mature virions. Using an R-site mutant A247S virus, we have recently shown that this mutant protease retains enzymatic activity but fails to support viral growth, suggesting that the release of N0 is required for viral replication. Here we report that another mutant protease, with an amino acid substitution (Ser to Cys) at the active site, can complement the A247S mutant but not a protease deletion mutant. Cell lines expressing the active-site mutant protease were isolated and shown to complement the A247S mutant at the levels of capsid assembly, DNA packaging, and viral growth. Therefore, the complementation between the R-site mutant and the active-site mutant reconstituted wild-type Pra function. One feature of this intragenic complementation is that following sedimentation of infected-cell lysates on sucrose gradients, both N-terminally unprocessed and processed proteases were isolated from the fractions where normal B capsids sediment, suggesting that proteolytic processing occurs inside capsids. Our results demonstrate that the HSV-1 protease has distinct functional domains and some of these functions can complement in trans.

Release of the catalytic domain N(o) from the herpes simplex virus type 1 protease is required for viral growth

The herpes simplex virus type 1 (HSV-1) protease and its substrate, ICP35, are involved in the assembly of viral capsids and required for efficient viral growth. The full-length protease (Pra) consists of 635 amino acid (aa) residues and is autoproteolytically processed at the release (R) site and the maturation (M) site, releasing the catalytic domain No (VP24), Nb (VP21), and a 25-aa peptide. To understand the biological importance of cleavage at these sites, we constructed several mutations in the cloned protease gene. Transfection assays were performed to determine the functional properties of these mutant proteins by their abilities to complement the growth of the protease deletion mutant m100. Our results indicate that (i) expression of full-length protease is not required for viral replication, since a 514-aa protease molecule lacking the M site could support viral growth; and that (ii) elimination of the R site by changing the residue Ala-247 to Ser abolished viral replication. To better understand the functions that are mediated by proteolytic processing at the R site of the protease, we engineered an HSV-1 recombinant virus containing a mutation at this site. Analysis of the mutant A247S virus demonstrated that (i) the mutant protease retained the ability to cleave at the M site and to trans process ICP35 but failed to support viral growth on Vero cells, demonstrating that release of the catalytic domain No from Pra is required for viral replication; and that (ii) only empty capsid structures were observed by electron microscopy in thin sections of A247S-infected Vero cells, indicating that viral DNA was not encapsidated. Our results demonstrate that processing of ICP35 is not sufficient to support viral replication and provide genetic evidence that the HSV-1 protease has nuclear functions other than enzymatic activity.

The product of the UL6 gene of herpes simplex virus type 1 is associated with virus capsids

We report on the analysis of the UL6 and UL7 open reading frames of the herpes simplex virus type 1 (HSV-1) genome. The UL6 and UL7 transcripts were identified in HSV-1-infected cells by Northern blotting and shown to be coterminal at their 3' ends. Both transcripts were synthesized in the presence of phosphonoacetic acid, although in reduced amounts, indicating that UL6 and UL7 are expressed as delayed-early or gamma-1 genes. The 5' ends of the two transcripts were mapped by S1 nuclease and primer extension analysis. A polyclonal antiserum directed against an Escherichia coli-expressed 6 x His-UL6 fusion protein identified a protein of approximate M(r) 75,000 in cells infected with either HSV-1 or with a vaccinia virus recombinant expressing the HSV-1 UL6 protein. As with the transcript, the UL6 protein was synthesized at reduced levels in the absence of viral DNA replication. Western immunoblotting showed that the UL6 protein was present in purified virions but not in L-particles of HSV-1, and that it was located exclusively in the tegument/capsid fraction of virion. Further analysis of the UL6 protein revealed that this protein was associated with virus capsids.

Phenotype of the herpes simplex virus type 1 protease substrate ICP35 mutant virus

The herpes simplex virus type 1 ICP35 assembly protein is involved in the formation of viral capsids. ICP35 is encoded by the UL26.5 gene and is specifically processed by the herpes simplex virus type 1 protease encoded by the UL26 gene. To better understand the functions of ICP35 in infected cells, we have isolated and characterized an ICP35 mutant virus, delta ICP35. The mutant virus was propagated in complementing 35J cells, which express wild-type ICP35. Phenotypic analysis of delta ICP35 shows that (i) mutant virus growth in Vero cells was severely restricted, although small amounts of progeny virus was produced; (ii) full-length ICP35 protein was not produced, although autoproteolysis of the protease still occurred in mutant-infected nonpermissive cells; (iii) viral DNA replication of the mutant proceeded at wild-type levels, but only a very small portion of the replicated DNA was processed to unit length and encapsidated; (iv) capsid structures were observed in delta ICP35-infected Vero cells by electron microscopy and by sucrose sedimentation analysis; (v) assembly of VP5 into hexons of the capsids was conformationally altered; and (vi) ICP35 has a novel function which is involved in the nuclear transport of VP5.

The size and symmetry of B capsids of herpes simplex virus type 1 are determined by the gene products of the UL26 open reading frame

Herpes simplex virus type 1 (HSV-1) B capsids are composed of seven proteins, designated VP5, VP19C, 21, 22a, VP23, VP24, and VP26 in order of decreasing molecular weight. Three proteins (21, 22a, and VP24) are encoded by a single open reading frame (ORF), UL26, and include a protease whose structure and function have been studied extensively by other investigators. The protease encoded by this ORF generates VP24 (amino acids 1 to 247), a structural component of the capsid and mature virions, and 21 (residues 248 to 635). The protease also cleaves C-terminal residues 611 to 635 of 21 and 22a, during capsid maturation. Protease activity has been localized to the N-terminal 247 residues. Protein 22a and probably the less abundant protein 21 occupy the internal volume of capsids but are not present in virions; therefore, they may form a scaffold that is used for B capsid assembly. The objective of the present study was to isolate and characterize a mutant virus with a null mutation in UL26. Vero cells were transformed with plasmid DNA that encoded ORF UL25 through UL28 and screened for their ability to support the growth of a mutant virus with a null mutation in UL27 (K082). Four of five transformants that supported the growth of the UL27 mutant also supported the growth of a UL27-UL28 double mutant. One of these transformants (F3) was used to isolate a mutant with a null mutation in UL26. The UL26 null mutation was constructed by replacement of DNA sequences specifying codons 41 through 593 with a lacZ reporter cassette. Permissive cells were cotransfected with plasmid and wild-type virus DNA, and progeny viruses were screened for their ability to grow on F3 but not Vero cells. A virus with these growth characteristics, designated KUL26 delta Z, that did not express 21, 22a, or VP24 during infection of Vero cells was isolated. Radiolabeled nuclear lysates from infected nonpermissive cells were layered onto sucrose gradients and subjected to velocity sedimentation. A peak of radioactivity for KUL26 delta Z that sedimented more rapidly than B capsids from wild-type-infected cells was observed. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the gradient fractions showed that the peak fractions contained VP5, VP19C, VP23, and VP26. Analysis of sectioned cells and of the peak fractions of the gradients by electron microscopy revealed sheet and spiral structures that appear to be capsid shells.(ABSTRACT TRUNCATED AT 400 WORDS)

The protease of herpes simplex virus type 1 is essential for functional capsid formation and viral growth

The herpes simplex virus type 1 protease and related proteins are involved in the assembly of viral capsids. The protease encoded by the UL26 gene can process itself and its substrate ICP35, encoded by the UL26.5 gene. To better understand the functions of the protease in infected cells, we have isolated a complementing cell line (BMS-MG22) and constructed and characterized a null UL26 mutant virus, m100. The mutant virus failed to grow on Vero cells and required a complementing cell line for its propagation, confirming that the UL26 gene product is essential for viral growth. Phenotypic analysis of m100 shows that (i) normal amounts of the c and d forms of ICP35 were produced, but they failed to be processed to the cleaved forms, e and f; (ii) viral DNA replication of the mutant proceeded at near wild-type levels, but DNA was not processed to unit length or encapsidated; (iii) capsid structures were observed in thin sections of m100-infected Vero cells by electron microscopy, but assembly of VP5 into hexons of the capsid structure was conformationally altered; and (iv) nuclear localizations of the protease and ICP35 are independent of each other, and the function(s) of Na, at least in part, is to direct the catalytic domain N(o) to the nucleus.

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.

Flow cytometric indirect immunofluorescence assay with high sensitivity and specificity for the detection of antibodies to HSV-1 and HSV-2

Cells infected with HSV-1 or HSV-2 develop viral antigens which can be detected by immunofluorescence. We developed a flow cytometric indirect immunofluorescence assay to detect and quantitate antibodies to HSV-1 and HSV-2 in human sera. Results obtained by flow cytometry for detecting antibodies against HSV-1, when compared with results obtained by ELISA, showed an index of overall agreement of 100%. The correlation between the antibody titers obtained with each method was found to be highly significant. An index of overall agreement equal to 94.1% was observed between results obtained by flow cytometry and by immunofluorescence as concerns the discrimination of HSV-2 positive from negative samples. However, the correlation between antibody titers was found to be not statistically significant. The flow cytometric assay proved to be type-specific.

Herpes simplex virus type 1 DNA cleavage and encapsidation require the product of the UL28 gene: isolation and characterization of two UL28 deletion mutants

The herpes simplex virus type 1 UL28 gene contains a 785-amino-acid open reading frame that codes for an essential protein. Studies with temperature-sensitive mutants which map to the UL28 gene indicate that the UL28 gene product (ICP18.5) is required for packaging of viral DNA and for expression of viral glycoproteins on the surface of infected cells (C. Addison, F. J. Rixon, and V. G. Preston, J. Gen. Virol. 71:2377-2384, 1990; B. A. Pancake, D. P. Aschman, and P. A. Schaffer, J. Virol. 47:568-585, 1983). In this study, we describe the isolation of two UL28 deletion mutants that were constructed and propagated in Vero cells transformed with the UL28 gene. The mutants, gCB and gC delta 7B, contained deletions of 1,881 and 537 bp, respectively, in the UL28 gene. Although the mutants synthesize viral DNA, they fail to form plaques or produce infectious virus in cells that do not express the UL28 gene. Transmission electron microscopy and Southern blot analysis demonstrated that both mutants are defective in cleavage and encapsidation of viral DNA. Analysis by cell surface immunofluorescence showed that the UL28 gene is not required for expression of viral glycoproteins on the surface of infected cells. A rabbit polyclonal antiserum was made against an Escherichia coli-expressed Cro-UL28 fusion protein. This antibody reacted with an infected-cell protein having an apparent molecular mass of 87 kDa. The 87-kDa protein was first detected at 6 h postinfection and was expressed as late as 24 h postinfection. No detectable UL28 protein was synthesized in gCB- or gC delta 7B-infected Vero cells.

Mutations in herpes simplex virus type 1 genes encoding VP5 and VP23 abrogate capsid formation and cleavage of replicated DNA

The herpes simplex virus type 1 capsid is composed of seven capsid proteins which are termed VP5, VP19c, VP21, VP22a, VP23, VP24, and VP26. Major capsid protein VP5 is encoded by the gene UL19. UL18, whose transcript is 3' coterminal with that of VP5, specifies capsid protein VP23. Vero cell lines have been isolated that are transformed with either the BglII N (UL19) or EcoRI G (UL16 to UL21) fragment of KOS. These cell lines, selected for the ability to support the replication of a temperature-sensitive VP5 mutant, were used to isolate VP5 and VP23 null mutants. The mutations in VP5 (K5 delta Z) and VP23 (K23Z) were generated by insertion of the lacZ gene at the beginning of the coding sequences of the genes. Both mutants failed to form plaques on the nonpermissive cell line, and therefore, VP23, like VP5, is an essential gene product for virus replication. Both mutants expressed wild-type levels of infected-cell proteins upon infection of permissive and nonpermissive cell lines. However, the VP5 (150-kDa) and VP23 (33-kDa) polypeptides were absent in lysates prepared from K5 delta Z- and K23Z-infected Vero cells, respectively. No capsid structures were observed by electron microscopic analysis of thin sections of K5 delta Z- and K23Z-infected Vero cells. Following sedimentation of lysates from cells infected by the mutants, capsid proteins were not observed in the fractions where capsids normally sediment. The amounts of DNA replicated in the VP5 and VP23 mutant and in KOS-infected Vero cells were the same as in permissive cells. However, genomic ends were not evident in Vero cells infected with the mutants, suggesting that the DNA remains in concatemers and is not processed into unit length genomes.

Posttranslational modification and subcellular localization of the p12 capsid protein of herpes simplex virus type 1

We have previously shown that the 12-kDa capsid protein (p12) of herpes simplex virus type 1 (HSV-1) is a gamma 2 (true late) gene product encoded by the UL35 open reading frame (D. S. McNabb and R. J. Courtney, J. Virol. 66:2653-2663, 1992). To extend the characterization of p12, we have investigated the posttranslational modifications and intracellular localization of the 12-kDa polypeptide. These studies have demonstrated that p12 is modified by phosphorylation at serine and threonine residues. In addition, analysis of p12 by acid-urea gel electrophoresis has indicated that the protein can be resolved into three components, designated p12a, p12b, and p12c. Using isotopic-labeling and alkaline phosphatase digestion experiments, we have determined that p12a and p12b are phosphorylated forms of the protein, and p12c is likely to represent the unphosphorylated polypeptide. The kinetics of phosphorylation was examined by pulse-chase radiolabeling, and these studies indicated that p12c can be completely converted into p12a and p12b following a 4-h chase. All three species of p12 were found to be associated with purified HSV-1 virions; however, p12b and p12c represented the most abundant forms of the protein within viral particles. We have also examined the intracellular localization of p12 by cell fractionation and indirect immunofluorescence techniques. These results indicated that p12 is predominantly localized in the nucleus of HSV-1-infected cells and appears to be restricted to specific regions within the nucleus.

Processing of the herpes simplex virus assembly protein ICP35 near its carboxy terminal end requires the product of the whole of the UL26 reading frame

The herpes simplex virus (HSV) type 1 assembly protein ICP35 consists of a family of polypeptides, ranging in molecular weight from about 45,000-39,000. The lower molecular weight forms of ICP35 are derived from the higher molecular weight species by slow post-translational modification. The reading frame of gene UL26 and the region within this gene which exhibited homology to the cytomegalovirus assembly protein, the analogous protein to ICP35, were expressed separately under immediate-early (IE) gene regulation in a HSV vector containing a temperature-sensitive mutation in the major transcriptional regulator Vmw175. Monoclonal antibody specific for ICP35 immunoprecipitated several polypeptides with molecular weights around 75,000 from extracts of cells infected with a recombinant expressing the IE gene UL26 at the nonpermissive temperature (NPT). These results suggested that the UL26 gene specified a protein distinct from ICP35 but which had some antigenic sites in common with ICP35. In extracts of cells infected at the NPT with a recombinant expressing only the carboxy terminal half of UL26 coding sequences, the monoclonal antibody immunoprecipitated large amounts of the high molecular weight forms of ICP35. The lower molecular weight processed forms of ICP35, however, were not detectable. When cells were coinfected with both recombinants ICP35 was processed to its lower molecular weight forms. This processing step, which occurred near the carboxy terminus of ICP35, was not dependent on capsid formation. The work, together with previous information on the processing of the CMV assembly protein, suggests that UL26 product may be a protease.

The herpes simplex virus UL33 gene product is required for the assembly of full capsids

Phenotypic analysis of the herpes simplex virus type 1 temperature-sensitive DNA-positive mutant, ts1233, revealed that the mutant had a structural defect at the nonpermissive temperature (NPT). Cells infected with ts1233 at the NPT contained large numbers of intermediate capsids, lacking dense cores but possessing some internal structure. No full capsids or enveloped virus particles were detected. In contrast to the defect in another packaging-deficient mutant ts1201, the block in the formation of dense-cored, DNA-containing capsids in ts1233-infected cells at the NPT could not be reversed by transferring the cells to the permissive temperature in the presence of a protein synthesis inhibitor. Furthermore, the capsids produced by ts1233 at the NPT had more compact internal structures than those of the gene UL26 mutant ts1201. Southern blot analysis of viral DNA in ts1233-infected cells confirmed that the mutant DNA was not encapsidated at the NPT and showed that the unpackaged DNA was not cleaved into genome-length molecules. The ts1233 mutation was mapped by marker rescue to the vicinity of genes UL32 and UL33. Sequence analysis of the DNA in this region from the mutant and two independently isolated revertants for growth revealed that ts1233 had a single base-pair change at the amino-terminal end of UL33, resulting in the substitution of an isoleucine with an asparagine. The nucleotide sequence of the revertants in this part of the genome was identical to that of wild-type virus.

Identification of precursor to cytomegalovirus capsid assembly protein and evidence that processing results in loss of its carboxy-terminal end

The 37-kilodalton (kDa) assembly protein of cytomegalovirus (strain Colburn) B capsids is shown to have a 40-kDa precursor. Pulse-chase radiolabeling experiments revealed that conversion of the precursor to the product was slow, requiring over 6 h for completion, and correlated with movement from the cytoplasmic to the nuclear fraction of Nonidet P-40-disrupted cells. Of these two proteins, only the 40-kDa precursor was synthesized in vitro from infected-cell RNA, consistent with its being the primary translation product. Amino acid sequence data obtained from CNBr-treated, high-performance liquid chromatography-purified assembly protein indicated that precursor translation begins at the first of two closely spaced potential initiation sites and that precursor maturation involves the loss of at least 32 amino acids from its carboxy-terminal end. It is also shown by immunological cross-reactivity and peptide similarity that three low-abundance B-capsid proteins (i.e., the 45-kilodalton [45K], 39K, and 38K proteins) are closely related to the assembly protein; the nature of this relatedness is discussed.

Physical mapping and nucleotide sequence of a herpes simplex virus type 1 gene required for capsid assembly

In this report, we describe some phenotypic properties of a temperature-sensitive mutant of herpes simplex type 1 (HSV-1) and present data concerning the physical location and nucleotide sequence of the genomic region harboring the mutation. The effect of shifts from the permissive to the nonpermissive temperature on infectious virus production by the mutant A44ts2 indicated that the mutated function is necessary throughout, or late in, the growth cycle. At the nonpermissive temperature, no major differences were detected in viral DNA or protein synthesis with respect to the parent A44ts+. On the other hand, electron microscopy of mutant-infected cells revealed that neither viral capsids nor capsid-related structures were assembled at the nonpermissive temperature. Additional analyses employing the Hirt extraction procedure showed that A44ts2 is also unable to mature replicated viral DNA into unit-length molecules under nonpermissive conditions. The results of marker rescue experiments with intact A44ts2 DNA and cloned restriction fragments of A44ts+ placed the lesion in the coordinate interval 0.553 to 0.565 (1,837 base pairs in region UL) of the HSV-1 physical map. No function has previously been assigned to this region, although it is known to be transcribed into two 5' coterminal mRNAs which code in vitro for a 54,000-molecular-weight polypeptide (K. P. Anderson, R. J. Frink, G. B. Devi, B. H. Gaylord, R. H. Costa, and E. K. Wagner, J. Virol. 37:1011-1027, 1981). We sequenced the interval 0.551 to 0.565 and found an open reading frame (ORF) for a 50,175-molecular-weight polypeptide. The predicted product of this ORF exhibits strong homology with the product of varicella-zoster virus ORF20 and lower, but significant, homology with the product of Epstein-Barr virus BORF1. For the three viruses, the corresponding ORFs lie just upstream of the gene coding for the large subunit of viral ribonucleotide reductase. The ORF described here corresponds to the ORF designated UL38 in the recently published nucleotide sequence of the HSV-1 UL region (D. J. McGeoch, M. A. Dalrymple, A. J. Davison, A. Dolan, M. C. Frame, D. McNab, L. J. Perry, J. E. Scott, and P. Taylor, J. Gen. Virol. 69:1531-1574, 1988).

Simian alphaherpesviruses and their relation to the human herpes simplex viruses

Biochemical and immunological properties of structural and non-structural polypeptides of the human simplex viruses (HSV1 and HSV2) and four related herpesviruses of non-human primates [Herpesvirus simiae (B virus), H. cercopithicus (SA8), H. saimiri 1 (HVS 1), and H. ateles 1 (HVA 1)] were compared. Using a radioimmunoassay (RIA), the presence of antigenic determinants shared among all six viruses was demonstrated. The relative degree of antigenic cross-reactivity among these viruses was further assessed by competition RIA. Antigenically, HSV 1 and HSV 2 were most closely related to each other although both SA 8 and B virus were also very closely related to HSV 1. Considerably less cross-reactivity existed between either HVS 1 or HVA 1 and the other four primate herpesviruses. Cross-hybridization between simian and human herpesvirus genomes demonstrated that extensive homology exists between each of the simian viruses and both HSV1 and HSV 2. Viral polypeptides bearing common antigenic determinants were identified by immune precipitation of infected cell polypeptides and by immunoblotting. Among the polypeptides of HSV which were recognized by antisera to simian viruses were the VP 5 and p40 proteins, both of which are structural components of the virion nucleocapsid. Using recombinant plasmids containing sequences of the HSV 1 VP5, p40, DNA polymerase, major DNA binding protein, and TK enzyme genes, homologous sequences were detected in all four simian viruses. Together, these results demonstrate that HSV 1, HSV 2, SA 8, and B virus form a closely related sub-group of the primate herpesviruses; HVS 1 and HVA 1 are also related to the other four primate herpesviruses, albeit more distantly.

Primate cytomegalovirus assembly: evidence that DNA packaging occurs subsequent to B capsid assembly

Results presented here show that when cytomegalovirus (strain Colburn)-infected cells are treated with the DNA synthesis inhibitor hydroxyurea or phosphonoformate, one type of intranuclear capsid accumulates. These particles appeared to contain symmetrically organized internal material, and had a protein composition and sedimentation rate characteristic of B capsids. Radiolabeling experiments provided evidence that a population of B capsids lacking DNA is present during the course of a normal infection. These capsids sedimented slightly slower than the peak of viral DNA in the same region of the gradient, and had a ratio of DNA/protein that was estimated to be sevenfold lower than that of the faster sedimenting C capsids. DNA in both the B and C capsid regions of such gradients was found to be relatively resistant to digestion with DNase. The possibility is considered that herpesvirus B capsids lacking DNA may be counterparts of unexpanded proheads in the bacteriophage assembly pathway.

Characterization of intranuclear capsids made by ts morphogenic mutants of HSV-1

We have characterized capsids made by seven temperature-sensitive (ts) mutants of HSV-1 previously shown to be defective in viral DNA processing and packaging at the nonpermissive temperature (NPT). The empty capsids isolated from mutant-infected cells at the NPT were devoid of DNA, cosedimented in sucrose with wt B capsids, and contained the same structural proteins found in wt B capsids (W. Gibson and B. Roizman (1972). J. Virol. 10, 1044-1052). The presence of VP22a in empty capsids suggests that the processing of this protein from higher-molecular-weight precursors and its association with capsids is required, but not sufficient, for DNA encapsidation. Mutants made no detectable A capsids at the NPT, but did so at the permissive temperature (PT), suggesting that A particles are generated during or subsequent to, rather than prior to, encapsidation. In temperature-shift experiments, it was demonstrated that capsids of one of the mutants, F18, made at the NPT did not participate in DNA encapsidation when cells were subsequently shifted to the PT. Only those capsids made after temperature shift to the PT acquired viral DNA, implying that the ts mutation in F18 may lie in a gene coding for a structural protein, or in a protein involved in the processing of viral DNA.

Detection of herpes simplex virus proteins in cultured cells by monoclonal antibodies and the avidin-biotin-immunoperoxidase complex method

The distribution of 5 proteins of herpes simplex virus Type 1 was observed in cells that had been infected for various periods. The cells were stained with monoclonal antibodies to ICP4, ICP5, ICP6, ICP8, and gB, using the avidin-biotin-peroxidase complex (ABC) method. Each protein had a characteristic pattern of time of appearance and translocation by which it could be distinguished from the others. The sensitivity of the ABC technique, its ease of use, and the permanence of the preparations make this method well suited for the study of viral proteins.

Varicella-zoster virus p32/p36 complex is present in both the viral capsid and the nuclear matrix of the infected cell

Varicella-zoster virus (VZV) directs the synthesis of numerous glycosylated and nonglycosylated infected-cell-specific proteins, many of which are later incorporated into the virion as structural components. In this study, we characterized a nonglycosylated polypeptide complex with the aid of a VZV-specific murine monoclonal antibody clone, 251D9. As detected by indirect immunofluorescence, the antibody bound mainly to antigens located within the nuclei of infected cells and did not attach to an uninfected cell substrate. The polypeptide specificity of the monoclonal antibody was determined by immunoblot analysis of electrophoretically separated infected cell extracts to react with a 32,000-molecular-weight VZV-specific protein (p32); in addition, the antibody also bound to a 36,000-molecular-weight polypeptide. The synthesis of these antigens was unaffected by inhibitors of glycosylation. Nonionic or ionic detergents were only marginally effective in solubilization of the p32-p36 complex, and relatively small amounts were eluted from nuclei by high salt concentrations (2 M NaCl). The same proteins remained associated with the nuclear matrix of VZV-infected cells. We also demonstrated that the protein complex was a major component of purified VZV nucleocapsids; p32 was especially prominent in both full and empty capsids. Immunoblot analysis of the nucleocapsid preparation revealed two additional species (p34 and p38) in the p32-p36 complex. Phosphorylation was a distinctive feature of some of the constituents. In summary, these results indicate that the p32-p36 complex represents a family of structural proteins closely associated with the assembly of VZV nucleocapsids and the encapsidation of viral DNA.

Isolation of human cytomegalovirus intranuclear capsids, characterization of their protein constituents, and demonstration that the B-capsid assembly protein is also abundant in noninfectious enveloped particles

Two types of intranuclear capsids have been recovered from human cytomegalovirus (HCMV, strain AD169)-infected cells. By analogy with strain Colburn (simian CMV) particles, these have been designated as A- and B-capsids. Both types of capsids are composed of proteins with molecular weights of 153,000 (major capsid protein), 34,000 (minor capsid protein), 28,000, and 11,000 (smallest capsid protein). In addition to these species, B-capsids contain a 36,000-molecular-weight (36K) protein which has been designated as the HCMV "assembly protein," based on its similarities to counterparts in strain Colburn CMV (i.e., 37K protein) and herpes simplex virus (i.e., VP22a/p40/NC-3/ICP35e). Peptide comparisons established that the assembly protein of HCMV B-capsids and the 36K protein that distinguishes HCMV noninfectious enveloped particles from virions are the same, providing direct evidence that noninfectious enveloped particles are enveloped B-capsids.

Gel electrophoretic analysis of polypeptides from nucleocapsids of Marek's disease virus strains and herpesvirus of turkey

The polypeptides of nucleocapsids of Marek's disease virus (MDV) strains with different biological properties and of antigenically related herpesvirus of turkey (HVT) strains were analysed by one- and two-dimensional (1D and 2D, respectively) gel electrophoresis. Based on small differences in migration behaviour (size and charge) of a number of corresponding nucleocapsid polypeptides, the virus strains could be differentiated into three groups. The polypeptide pattern of group I, comprising the virulent MDV-strain K and the attenuated strains, HPRS-16/att and CVI988 37th passage, was composed of four major polypeptides (i.e. 140K, 50K, 40K and 33K daltons) and at least four minor polypeptides. The pattern of group II, comprising the naturally occurring non-oncogenic MDV-strains SB-1 and HPRS-24, contained one additional major polypeptide of 39K daltons. The nucleocapsid-specific 2D polypeptide patterns of the HVT strains HVT-Fc 126 and PB-THV1, comprising group III, were distinguishable from each other on the basis of a small difference in size of one major 50K polypeptide. Results were further substantiated by coelectrophoresis experiments.

The immune response to herpes simplex virus: comparison of the specificity and relative titers of serum antibodies directed against viral polypeptides following primary herpes simplex virus type 1 infections

Employing an immunoblotting technique, the polypeptide specificity and relative titers of anti-HSV IgG reactive with denaturation-resistant epitopes on HSV proteins were determined in patients experiencing primary HSV-1 infections at various anatomical sites. Early sera from previously seronegative patients with primary HSV-1 infections were found to have comparatively low levels of antibody directed against the major viral glycoprotein antigens (gB, gC, and gD) relative to titers present in sera of individuals with long-standing, latent orofacial HSV-1 infections. Patients with primary infections did however have high titers of antibody directed against a series of low molecular weight HSV polypeptide antigens. These antigens were found to be antigenically related to a structural component of virion nucleocapsids. At later times postinfection, titers of antibodies directed against other viral polypeptides including the major glycoproteins increased to levels more closely approximating those observed in latently infected individuals. These results indicate that the anti-HSV IgG detected by immunoblot analysis which appears earliest following primary infection is not directed against the known major infected cell or virion glycoprotein surface antigens but rather against an internal capsid protein of HSV.

Enzyme-linked immunosorbent assay for determination of antibodies against herpes simplex virus types 1 and 2 in human sera

A rapid and reproducible enzyme-linked immunosorbent assay (ELISA) is described for determining antibodies in human sera against herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2). The sera were absorbed for 30 min with heterologous virus-infected-cell extracts to remove cross-reacting antibodies and then were applied to ELISA plates containing the target antigens, immunoaffinity-purified HSV-1 glycoproteins gC and gD and HSV-2 glycoproteins gD and gF. The absorbance index, defined as the ratio of A414 generated by a serum sample absorbed with a heterologous virus-infected-cell extract versus the A414 of a serum sample absorbed with an uninfected-cell extract, was used to determine the presence or absence of antibodies to HSV-1 and HSV-2. Results of the ELISA for detecting antibodies against HSV-2, when compared with results obtained for the same sera by the microneutralization test, showed an index of overall agreement of 91%. Results of the ELISA for detecting antibodies against HSV-1, when compared with microneutralization test results for sera negative for HSV-2 antibodies but positive for HSV antibodies by ELISA, showed an index of agreement of 99%.

Characterisation of a herpes simplex virus type 1 mutant which has a temperature-sensitive defect in penetration of cells and assembly of capsids

A herpes simplex virus type 1 (HSV-1) mutant, ts1204, which has a temperature-sensitive (ts) mutation located within genome map coordinates 0.318 to 0.324, close to but outside the coding sequences of the glycoprotein gB gene, has been characterised. Although this mutant adsorbed to the cell surface at the nonpermissive temperature (NPT), it failed to penetrate the cell membrane. As a consequence of this defect, high multiplicities of infection of ts1204 blocked subsequent infection of cells by wild-type HSV-1. By contrast, at the NPT, superinfection of cells with HSV-2 was not inhibited by prior infection with ts1204. The penetration defect could be overcome either by brief incubation of mutant virus-infected cells at the permissive temperature, or by treatment of the cells with polyethylene glycol, a compound which promotes fusion of membranes. Upon continued incubation of ts1204-infected cells at the NPT, low numbers of capsids were assembled. Although these capsids all had some internal structure, they did not contain DNA. Another mutant, ts1208, which lies in the same complementation group as ts1204, penetrated cells normally at the NPT, but like ts1204, had a defect in the formation of functional capsids. Evidence presented in this paper suggests that the gene in which the ts1204 and ts1208 lesions map encodes a structural polypeptide.

Replication of simian herpesvirus SA8 and identification of viral polypeptides in infected cells

The replication of the simian herpesvirus SA8 in Vero cells was examined. The time course of replication of the simian herpesvirus SA8 was found to be similar to that of the herpes simplex viruses. Infectious progeny virions were first detectable by 6 h postinfection and were readily released into the extracellular fluids beginning at 9 h postinfection. All cell lines tested, with the exception of Madin-Darby canine kidney cells, were permissive for SA8. Analysis of SA8-infected cells by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed over 40 infected cell polypeptides ranging in molecular weight from 158,000 to less than 10,000. Of these proteins, 23 were present in virions. Three classes of infected cell polypeptides could be identified based on the kinetics of their synthesis. Post-translational processing of several SA8-induced proteins was also observed in pulse-chase experiments. Six distinct SA8-specific glycoproteins ranging from 118,000 to 19,500 daltons were also identified in infected cells. Of these glycoproteins, five were present in virions.

Characterization of post-translational products of herpes simplex virus gene 35 proteins binding to the surfaces of full capsids but not empty capsids

We report on the properties of a genetically and immunologically related family of structural (gamma) polypeptides of herpes simplex virus 1 designated as infected cell polypeptides (ICP) 35. The members of this family were identified and studied with the aid of a panel of monoclonal antibodies exemplified by H745. This monoclonal antibody reacted with six bands (ICP35a to 35f) formed by ICPs contained in either HEp-2 or Vero cell lysates electrophoretically separated in denaturing gels and transferred to nitrocellulose sheets. The six bands had apparent molecular weights in the range 39,000 to 50,000. Traces of ICP35 with apparent molecular weights of 37,000 were also observed in some preparations. On two-dimensional separation ICP35 family members formed at least 20 spots reactive with H745. These differed in both isoelectric properties and electrophoretic mobility in denaturing gels. Pulse-chase experiments, together with results published earlier, indicate that ICP35a to 35d are cytoplasmic precursors to nuclear products. One of these corresponds to virion protein 22a, a component of capsids containing DNA accumulating in the nuclei of infected cells. ICP35 was labeled by 32Pi added to the medium, but the extent of phosphorylation varied and may be a determinant of isoelectric properties. Iodination studies indicate that ICP35e and 35f are the predominant forms of ICP35 present on the surface of full, nuclear capsids containing DNA. None of the members of the ICP35 family were detected in empty capsids. Surface iodination labeled the major capsid protein (ICP5) of empty capsids, but not of full capsids, indicating that ICP35e and 35f coat the surface of the viral capsid and block access to sites for iodination of ICP5, the major capsid protein.

Identification and characterization of a herpes simplex virus gene product required for encapsidation of virus DNA

A mutant of herpes simplex virus type 1, 17tsVP1201, has a temperature-sensitive processing defect in a late virus polypeptide. Immunoprecipitation studies with monoclonal antibodies showed that the aberrant polypeptide in mutant virus-infected cells was the nucleocapsid polypeptide known as p40. Since a revertant, TS(+) for growth, processed the polypeptide normally under conditions restrictive for the mutant, the processing event must be essential for virus replication. Electron microscopic analysis of mutant virus-infected cells grown at the nonpermissive temperature revealed that the nuclei contained large aggregations of empty nucleocapsids possessing some internal structure. Therefore, although the mutant synthesized virus DNA at the nonpermissive temperature, the DNA was not packaged into nucleocapsids. When mutant virus-infected cells were shifted from 39 to 31 degrees C in the presence of cycloheximide, the polypeptide p40 was processed to lower-molecular-weight forms, and full nucleocapsids were detected in the cell nuclei. The aberrant polypeptide of the mutant, however, was not processed in cells mixedly infected with 17tsVP1201 and a revertant at the nonpermissive temperature, suggesting that the defect of the mutant was in the gene encoding p40 rather than in a gene of a processing enzyme.

Genetic relatedness of the genomes of equine herpesvirus types 1, 2, and 3

Genomic DNAs of equine herpesvirus type 1 (EHV-1), EHV-2 (equine cytomegalovirus), and EHV-3 were examined by reassociation kinetic and thermal denaturation analyses to determine the extent and degree of homology among the three viral DNAs. Results of reassociation analyses indicated a limited homology among the three EHV genomes. Homologous DNA sequences equivalent to 1.8 to 3.7 megadaltons between EHV-1 and equine cytomegalovirus, 7.6 to 8.2 megadaltons between EHV-1 and EHV-3, and 1.3 to 1.9 megadaltons between equine cytomegalovirus and EHV-3 were detected. Examination by thermal denaturation of the DNA homoduplexes and heteroduplexes formed during reassociation revealed a high degree of base pairing within the duplexes, suggesting that closely related sequences may be conserved among the genomes of EHV.

Comparison of an ELISA technique with quantal micro-neutralization test for serotyping of HSV-1 or HSV-2-infected patients

An enzyme-linked immunosorbent assay (ELISA) using semi-purified herpes simplex antigens extracted from cell nuclei was employed for typing of 32 sera collected from patients infected with HSV-1 or HSV-2. The results were in agreement with those obtained by the quantal micro-neutralization test. Moreover, sera with antibodies which could not be detected by micro-neutralization test could be typed by the ELISA technique according to the HSV isolates.

Monoclonal antibodies to herpes simplex virus type 1 proteins, including the immediate-early protein ICP 4

Monoclonal antibodies were prepared against herpes simplex virus type 1 (strain 14012) by two immunization procedures. Procedure A utilized infectious virus propagated in mouse cells, and procedure B utilized mouse cells infected with herpes simplex virus in the presence of cycloheximide and harvested 1 h after removal of the inhibitor. A total of 52 monoclonal antibodies were obtained against 10 herpes simplex virus proteins, including four glycosylated proteins (a 110,000-molecular-weight protein, gB, gC, and gD) and six nonglycosylated proteins (a 68,000-molecular-weight protein, ICP 9, ICP 8, ICP 6, ICP 5, and the immediate-early ICP 4). The antibodies were assayed against herpes simplex virus types 1 and 2 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of radioimmunoprecipitates, immunofluorescence, and neutralization. Using the reagents prepared, we concluded that the 110,000-molecular-weight protein, gD, ICP 9, ICP 9, ICP 6, and the 68,000-molecular-weight protein express both type-specific and cross-reactive antigenic determinants. In contrast, nine antibodies against gB all cross-reacted with herpes simplex virus type 2, whereas eight antibodies to gC all reacted type specifically.