Analysis of the nucleotide sequence of five genes at the left end of the unique short region of the equine herpesvirus 4 genome

The equine herpesvirus 1 IR6 protein that colocalizes with nuclear lamins is involved in nucleocapsid egress and migrates from cell to cell independently of virus infection

The equine herpesvirus 1 (EHV-1) IR6 protein forms typical rod-like structures in infected cells, influences virus growth at elevated temperatures, and determines the virulence of EHV-1 Rac strains (Osterrieder et al., Virology 226:243-251, 1996). Experiments to further elucidate the functions and properties of the IR6 protein were conducted. It was shown that the IR6 protein of wild-type RacL11 virus colocalizes with nuclear lamins very late in infection as demonstrated by confocal laser scan microscopy and coimmunoprecipitation experiments. In contrast, the mutated IR6 protein encoded by the RacM24 strain did not colocalize with the lamin proteins at any time postinfection (p.i.). Electron microscopical examinations of ultrathin sections were performed on cells infected at 37 and 40 degreesC, the latter being a temperature at which the IR6-negative RacH virus and the RacM24 virus are greatly impaired in virus replication. These analyses revealed that nucleocapsid formation is efficient at 40 degreesC irrespective of the virus strain. However, whereas cytoplasmic virus particles were readily observed at 16 h p.i. in cells infected with the wild-type EHV-1 RacL11 or an IR6-recombinant RacH virus (HIR6-1) at 40 degreesC, virtually no capsid translocation to the cytoplasm was obvious in RacH- or RacM24-infected cells at the elevated temperature, demonstrating that the IR6 protein is involved in nucleocapsid egress. Transient transfection assays using RacL11 or RacM24 IR6 plasmid DNA and COS7 or Rk13 cells, infection studies using a gB-negative RacL11 mutant (L11DeltagB) which is deficient in direct cell-to-cell spread, and studies using lysates of IR6-transfected cells demonstrated that the wild-type IR6 protein is transported from cell to cell in the absence of virus infection and can enter cells by a yet unknown mechanism.

The ORF47 and ORF66 putative protein kinases of varicella-zoster virus determine tropism for human T cells and skin in the SCID-hu mouse

The varicella-zoster virus (VZV) genes ORF47 and ORF66 are predicted to encode serine/threonine protein kinases, which are homologs of herpes simplex virus 1 (HSV-1) UL13, and US3. When mutants were constructed by inserting stop codons into ORF47 and ORF66, the recombinants ROka47S and ROka66S, as well as intact ROka replicated in tissue culture. In contrast, inoculation of human thymus/liver or skin implants in SCID-hu mice showed that ORF47 protein was required for viral growth in human T cells and skin. Eliminating ORF66 expression inhibited VZV infectivity for T cells partially but did not impair replication in skin compared with ROka. Infectivity for T cells and skin was restored when ROka47S virus was complemented by insertion of ORF47 into a distant, noncoding site. The ORF47 gene product is the first VZV protein identified as necessary for T cell tropism. It also is essential for skin infectivity in vivo, as is glycoprotein C. Expression of ORF66 did not compensate for the absence of the ORF47 protein. The requirement for ORF47 expression in T cells and skin indicates that this gene product, which is dispensable in vitro, has a critical role within differentiated cells that are essential targets for VZV pathogenesis in vivo.

Genomic organization of the canine herpesvirus US region

Canine herpesvirus (CHV) is an alpha-herpesvirus of limited pathogenicity in healthy adult dogs and infectivity of the virus appears to be largely limited to cells of canine origin. CHV's low virulence and species specificity make it an attractive candidate for a recombinant vaccine vector to protect dogs against a variety of pathogens. As part of the analysis of the CHV genome, the authors determined the complete nucleotide sequence of the CHV US region as well as portions of the flanking inverted repeats. Seven full open reading frames (ORFs) encoding proteins larger than 100 amino acids were identified within, or partially within the CHV US: cUS2, cUS3, cUS4, cUS6, cUS7, cUS8 and cUS9; which are homologs of the herpes simplex virus type-1 US2; protein kinase; gG, gD, gI, gE; and US9 genes, respectively. An eighth ORF was identified in the inverted repeat region, cIR6, a homolog of the equine herpesvirus type-1 IR6 gene. The authors identified and mapped most of the major transcripts for the predicted CHV US ORFs by Northern analysis.

An equine herpesvirus-1 gene 71 deletant is attenuated and elicits a protective immune response in mice

The pathogenesis of pulmonary infection and the immune response following intranasal inoculation of mice with two equine herpesvirus type 1 (EHV-1) deletion mutants have been assessed. The mutants, ED71 and ED75, have deletions in genes 71 (EUS4) and 75 (10K), respectively. Deletions were replaced by the Escherichia coli lacZ gene driven by the simian virus 40 (SV40) early promoter. It has previously been shown that the protein products of genes 71 and 75 are dispensable in vitro but that removal of gene 71 results in a defect in virus maturation and capsid envelopment which impairs the ability of mutant virus to spread via release and readsorption. This study demonstrated that the 192-kDa gene 71 product is required for full expression of virulence in mice, whereas the putative 10-kDa product of gene 75 has minimal effect. Both mutants exhibited the same tissue and cytotropism as wild-type EHV-1 and induced both humoral and cell-mediated immune responses indistinguishable from those induced by the parental strain. Irrespective of the reduced pathogenicity of the gene 71 mutant, infected mice were protected against a challenge with wild-type EHV-1. These findings highlight the potential of ED71 as a vaccine candidate.

The highly O-glycosylated glycoprotein gp2 of equine herpesvirus 1 is encoded by gene 71

There have been conflicting reports regarding the gene assignment of the high-molecular-mass envelope glycoprotein gp2 (gp300) of equine herpesvirus 1. Here, we provide an unequivocal demonstration that gp2 is encoded by gene 71. gp2 that was purified with a defining monoclonal antibody was cleaved internally to yield a 42-kDa protein encoded by gene 71. Amino acid composition data and N-terminal sequence analysis of a tryptic peptide identified gp2 as the product of equine herpesvirus 1 gene 71 with the SWISS-PROT database. Analysis of gp2's monosaccharide composition and the 42-kDa subunit showed that the high level of O glycosylation occurs on the serine/threonine-rich region upstream of the cleavage site.

The nucleotide sequence of asinine herpesvirus 3 glycoprotein G indicates that the donkey virus is closely related to equine herpesvirus 1

The nucleotide sequence of the glycoprotein G (gG) homologue of asinine herpesvirus 3 (AHV3), a respiratory alphaherpesvirus of donkeys, was determined. The AHV3 gG gene consists of 1233 base pairs (bp) and codes for a predicted protein of 411 amino acids. This is identical in size to the equine herpesvirus 1 (EHV1) gG gene and 6 amino acids longer than the equine herpesvirus 4 (EHV4) gG gene. The predicted amino acid sequence of AHV3 gG has characteristics of a class 1 membrane protein. The amino acid sequence of AHV3 gG shows 92% and 60% identity to EHV1 gG and EHV4 gG respectively. Two regions within the gG amino acid sequences of EHV1 and EHV4 were previously defined, an N-terminal constant region and an immunodominant highly variable region located toward the C-terminus. In the corresponding constant region of AHV3 gG there was 96% and 75% amino acid identity with EHV1 and EHV4 gGs respectively. In the variable region, there was 73% and 24% identity respectively. Phylogenetic analyses using the gG nucleotide sequences indicated that AHV3 is much closer in evolutionary distance to EHV1 than either virus is to EHV4. These findings provide additional support for the view that AHV3, or another closely related virus, may be the progenitor of EHV1 and has adapted to horses in relatively recent times.

Transcriptional analyses of the unique short segment of EHV-1 strain Kentucky A

The unique short (Us) segment of the genome of equine herpesvirus type 1 (EHV-1) strain KyA is comprised of six open reading frames (ORFs) that encode: a) a homolog of the Us2 protein of herpes simplex virus type 1 (HSV-1); b) a serine threonine protein kinase that is a homolog of the HSV-1 Us3 protein; c) a homolog of pseudorabies virus glycoprotein gX and HSV-2 gG; d) a novel glycoprotein, EUS4, not encoded by other herpesviruses sequenced to date; e) a homolog of HSV-1 gD; and f) a homolog of HSV-1 Us9. The KyA strain is a deletion mutant that lacks Us sequences encoding gI, gE, and a potential 10 kD polypeptide, and thus may be useful as a parent virus for the generation of live virus vaccines. To complete the elucidation of the transcriptional program of the Us segment, Northern blot hybridization and S1 nuclease analyses were performed on poly(A)(+)-selected RNA isolated from infected cells maintained under early (phosphonoacetic acid-block) and late conditions. The findings revealed that the gene (EUS2 ORF) encoding the protein kinase is expressed as an early 2.9 kb transcript that overlaps and is 3' coterminal with a 1.6 kb early transcript that encodes the gG/gX homolog (EUS3 ORF). Two transcripts of 1.6 kb and 5.8 kb are 5' coterminal and may both encode the novel glycoprotein gene EUS4. The 1.6 kb transcript terminates at a poly(A) signal site downstream of the EUS4 ORF, and the 5.8 kb transcript terminates within the inverted repeat (IR) segment. Overall, the transcriptional program of the EHV-1 KyA Us segment is complex and exhibits similarities to that of HSV-1 Us segment: a) transcripts arise from both DNA strands; b) some transcripts, including those mapping at the termini of the Us segment, extend into the IR segments and are 3' coterminal with the 1.2 kb IR6 transcript; c) at least one transcript reads through a functional polyadenylation signal; d) some transcripts encoding genes that lie in different reading frames exist as a family of overlapping mRNAs, some in an anti-sense manner. Lastly, of the six Us genes of the EHV-1 KyA strain, only those encoding the EHV-1 protein kinase and the HSV-2 gG/gX homolog are members of the early kinetic class.

The Marek's disease virus (MDV) unique short region: alphaherpesvirus-homologous, fowlpox virus-homologous, and MDV-specific genes

Despite its previous classification as a gammaherpesvirus, primarily due to its lymphotropism, Marek's disease virus (MDV), an oncogenic avian herpesvirus, is phylogenetically more related to the "neurotropic" alphaherpesviruses, characterized by its prototype, herpes simplex virus (HSV) (Buckmaster et al., 1988, J. Gen. Virol. 69, 2033-2042). In this report we present the DNA sequence of an 11,286-bp DNA segment encompassing the entire 11,160-bp-long Us region of the oncogenic avian herpesvirus, Marek's disease virus. Eleven open reading frames (ORFs) likely to code for proteins were identified; of these, 7 represent homologs exclusive to alphaherpesvirus S component genes. These include MDV counterparts of HSV US1 (ICP22), US2, US3 (a serine-threonine protein kinase), US6, US7, and US8 (HSV glycoproteins gD, gI, and gE, respectively), and US10. Three additional ORFs were identified with no apparent relation to any sequences currently present in the SwissProt or GenBank/EMBL databases, while a fourth was found to exhibit significant homology to an uncharacterized fowlpox virus (FPV) ORF. Having precisely identified the IRs-U(s) and U(s)-TRs junctions, we have corrected and clarified their previously reported locations. By characterizing genes encoding three new alphaherpesvirus-related homologs (US1, US8, and US10), completing the sequence for a fourth (US7), and identifying 2 new MDV-specific ORFs (SORF1 and SORF3) and a fowlpox homolog (SORF2), our sequence analysis of the "virulent" GA strain of MDV (vMDV) extends upon that of a 5255-bp segment located in the U(s) region of the "very virulent" RB1B strain of MDV (vvMDV) (Ross et al., 1991, J. Gen. Virol. 72, 939-947; 949-954). These two sequences were found to exhibit 99% identity at both nucleotide and predicted amino acid levels. Combined with the fact that MDV U(s) sequences failed to show statistically significant CpG deficiencies, our analysis is consistent with MDV bearing a closer phylogenetic relation to alphaherpesviruses than to gammaherpesviruses. Because alphaherpesvirus-specific U(s) region genes are primarily nonessential for virus replication, they are thought to be important biological property determinants. Thus, our sequence provides a foundation for further MDV studies aimed at resolving the apparent discrepancy between MDV's genetic and biologic properties.

Nucleotide sequence analysis of an infectious laryngotracheitis virus gene corresponding to the US3 of HSV-1 and a unique gene encoding a 67 kDa protein

The DNA sequence of 4005 nucleotides from the Kpnl O and part of Kpnl K fragments in the short unique region of infectious laryngotracheitis virus (ILTV) was determined. The sequence contained two complete and one partial open reading frames (ORFs). The partial ORF was open at the 5' end of the sequence and represented the NH2-terminal 118 amino acids (aa) of a polypeptide. Its partial predicted protein product exhibited significant homology to the US2 gene product of HSV-1 (herpes simplex virus type 1) and it homologs in other herpesviruses. ORF 2 is 471 aa long and could encode a protein of 53.8 kDa which shared aa homology with the protein kinases encoded by HSV-1 US3 and its gene homologs. Analysis of the ORF 2 aa sequence revealed domains characteristic of protein-serine/threonine (S/T) kinases of cellular and viral origin. The ORF 3 encoded a predicted protein of 601 aa (M(r) 67.5 kDa) which exhibited limited homology (18% overall identity) with the UL47 protein (major tegument protein) of HSV-1. Northern (RNA) blot hybridization and metabolic inhibitors were used to characterize the ILTV protein kinase and the 67K mRNAs. The data revealed that protein kinase is a gamma-1 gene encoding a 1.6 mRNa, while the 67K ORF is a gamma-2 gene encoding a 2 kb mRNA.

Identification and initial characterization of the IR6 protein of equine herpesvirus 1

The IR6 gene of equine herpesvirus 1 (EHV-1) is a novel gene that maps within each inverted repeat (IR), encodes a potential protein of 272 amino acids, and is expressed as a 1.2-kb RNA whose synthesis begins at very early times (1.5 h) after infection and continues throughout the infection cycle (C. A. Breeden, R. R. Yalamanchili, C.F. Colle, and D.J. O'Callaghan, Virology 191:649-660,1992). To identify the IR6 protein and ascertain its properties, we generated an IR6-specific polyclonal antiserum to a TrpE/IR6 fusion protein containing 129 amino acids (residues 134 to 262) of the IR6 protein. This antiserum immunoprecipitated a 33-kDa protein generated by in vitro translation of mRNA transcribed from a pGEM construct (IR6/pGEM-3Z) that contains the entire IR6 open reading frame. The anti-IR6 antibody also recognized an infected-cell protein of approximately 33 kDa that was expressed as early as 1 to 2 h postinfection and was synthesized throughout the infection cycle. A variety of biochemical analyses including radiolabeling the IR6 protein with oligosaccharide precursors, translation of IR6 mRNA in the presence of canine pancreatic microsomes, radiolabeling the IR6 protein in the presence of tunicamycin, and pulse-chase labeling experiments indicated that the two potential sites for N-linked glycosylation were not used and that the IR6 protein does not enter the secretory pathway. To address the possibility that the unique IR6 gene encodes a novel regulatory protein, we transiently transfected an IR6 expression construct into L-M fibroblasts alone or with an immediate-early gene expression construct along with a representative EHV-1 immediate-early, early, or late promoter-chloramphenicol acetyltransferase reporter construct. The results indicated that the IR6 protein does not affect the expression of these representative promoter constructs. Interestingly, the IR6 protein was shown to be phosphorylated and to associate with purified EHV-1 virions and nucleocapsids. Lastly, immunofluorescence and laser-scanning confocal microscopic analyses revealed that the IR6 protein is distributed throughout the cytoplasm at early times postinfection and that by 4 to 6 h it appears as "dash-shaped" structures that localize to the perinuclear region. At late times after infection (8 to 12 h), these structures assemble around the nucleus, and three-dimensional image analyses reveal that the IR6 protein forms a crown-like structure that surrounds the nucleus as a perinuclear network.

Glycoprotein E of pseudorabies virus and homologous proteins in other alphaherpesvirinae

This paper reviews biological properties of glycoprotein E (gE) of pseudorabies virus (Aujeszky's disease virus) and homologous proteins in other alphaherpesvirinae. It focuses on the gene encoding gE, conserved regions in the gE protein and its homologs, the complex of gE and gI, biological functions of gE in vitro and in vivo, the role of gE in latency and the role of gE in the induction of humoral and cellular immune responses. Special emphasis is placed on the use of gE as a marker protein in the control and eradication of pseudorabies virus.

Epitopes of glycoprotein G of equine herpesviruses 4 and 1 located near the C termini elicit type-specific antibody responses in the natural host

Specific serological diagnosis of equine herpesvirus 4 (EHV4; equine rhinopneumonitis virus) and EHV1 (equine abortion virus) hitherto has not been possible because of extensive antigenic cross-reactivity between these two closely related but distinct viruses. Recently, we identified EHV4 glycoprotein G (gG) and characterized it as a type-specific, secreted glycoprotein (B. S. Crabb, H. S. Nagesha, and M. J. Studdert, Virology 190:143-154, 1992). This paper shows that EHV1 gG also possesses type-specific epitopes and describes the localization of strong, type-specific epitopes to the apparently corresponding and highly variable regions comprising amino acids 287 to 382 of EHV4 gG and 288 to 350 of EHV1 gG. Fusion proteins expressing these variable regions reacted strongly and type specifically with sera from four foals, three of which were colostrum-deprived, specific-pathogen-free foals, whose history with respect to exposure to EHV4 or EHV1 was well-defined. These antigens provided the basis for the development of a single-well diagnostic enzyme-linked immunosorbent assay to distinguish horses infected with EHV4, EHV1, or both. Such a type-specific test provides for the first time the opportunity to differentiate antibodies to these viruses, and it has, therefore, important implications for understanding the epidemiology of these equine pathogens. Evidence for the existence of EHV1 in Australia 10 years prior to the first confirmed case of EHV1 abortion is presented.