Determination and analysis of the complete nucleotide sequence of human herpesvirus

Cytomegalovirus basic phosphoprotein (pUL32) binds to capsids in vitro through its amino one-third

The cytomegalovirus (CMV) basic phosphoprotein (BPP) is a component of the tegument. It remains with the nucleocapsid fraction under conditions that remove most other tegument proteins from the virion, suggesting a direct and perhaps tight interaction with the capsid. As a step toward localizing this protein within the molecular structure of the virion and understanding its function during infection, we have investigated the BPP-capsid interaction. In this report we present evidence that the BPP interacts selectively, through its amino one-third, with CMV capsids. Radiolabeled simian CMV (SCMV) BPP, synthesized in vitro, bound to SCMV B-capsids, and C-capsids to a lesser extent, following incubation with either isolated capsids or lysates of infected cells. Human CMV (HCMV) BPP (pUL32) also bound to SCMV capsids, and SCMV BPP likewise bound to HCMV capsids, indicating that the sequence(s) involved is conserved between the two proteins. Analysis of SCMV BPP truncation mutants localized the capsid-binding region to the amino one-third of the molecule--the portion of BPP showing the greatest sequence conservation between the SCMV and HCMV homologs. This general approach may have utility in studying the interactions of other proteins with conformation-dependent binding sites.

The carboxyl terminus of the human cytomegalovirus UL37 immediate-early glycoprotein is conserved in primary strains and is important for transactivation

The human cytomegalovirus (HCMV) UL37 exon 3 (UL37x3) open reading frame (ORF) encodes the carboxyl termini of two immediate-early glycoproteins (gpUL37 and gpUL37(M)). UL37x3 homologous sequences are not required for mouse cytomegalovirus (MCMV) growth in vitro; yet, they are important for MCMV growth and pathogenesis in vivo. Similarly, UL37x3 sequences are dispensable for HCMV growth in culture, but their requirement for HCMV growth in vivo is not known. To determine this requirement, we directly sequenced the complete UL37x3 gene in multiple HCMV primary strains. A total of 63 of the 310 amino acids in the UL37x3 ORF differ non-conservatively in one or more HCMV primary strains. The HCMV UL37x3 genetic diversity is non-random: the N-glycosylation (46/186 aa) and basic (9/15 aa) domains have the highest proportion of non-conservative variant amino acids. Nonetheless, most (15/17 signals) of the N-glycosylation signals are retained in all HCMV primary strains. Moreover, new N-glycosylation signals are encoded by 5/20 primary strains. In sharp contrast, the UL37x3 transmembrane (TM) ORF completely lacks diversity in all 20 HCMV sequenced primary strains, and only 1 of 28 cytosolic tail residues differs non-conservatively. To test the functional significance of the conserved carboxyl terminus, gpUL37 mutants lacking the TM and/or cytosolic tail were tested for transactivating activity. The gpUL37 carboxyl-terminal mutants are partially defective in hsp70 promoter transactivation even though they trafficked similarly to the wild-type protein into the endoplasmic reticulum and to mitochondria. From these results, we conclude that N-glycosylated gpUL37, particularly its TM and cytosolic domains, is important for HCMV growth in humans.

Products of US22 genes M140 and M141 confer efficient replication of murine cytomegalovirus in macrophages and spleen

Efficient replication of murine cytomegalovirus (MCMV) in macrophages is a prerequisite for optimal growth and spread of the virus in its natural host. Simultaneous deletion of US22 gene family members M139, M140, and M141 results in impaired replication of MCMV in macrophages and mice. In this study, we characterized the proteins derived from these three genes and examined the impact of individual gene deletions on viral pathogenesis. The M139, M140, and M141 gene products were identified as early proteins that localize to both the nucleus and cytoplasm in infected cells. Gene M139 encodes two proteins, of 72 and 61 kDa, while M140 and M141 each encode a single protein of 56 (pM140) and 52 (pM141) kDa, respectively. No role for the M139 proteins in MCMV replication in macrophages or mice was determined in these studies. In contrast, deletion of either M140 or M141 resulted in impaired MCMV replication in macrophages and spleen tissue. Replication of the M140 deletion mutant was significantly more impaired than that of the virus lacking M141. Further analyses revealed that the absence of the pM140 adversely affected pM141 levels by rendering the latter protein unstable. Since the replication defect due to deletion of M140 was more profound than could be explained by the reduced half-life of pM141, pM140 must exert an additional, independent function in mediating efficient replication of MCMV in macrophages and spleen tissue. These data indicate that the US22 genes M140 and M141 function both cooperatively and independently to regulate MCMV replication in a cell type-specific manner and, thus, to influence viral pathogenesis.

Herpesvirus homologues of cellular genes

For millions of years viruses have adapted strategies to interfere with the immune defense of the host, which in turn has to deal with this challenge. In general the antiviral defense remains one step behind the pathogen. To achieve this strategic advantage large DNA-containing Viruses encode cellular homologues that mimic or counteract key molecules of the host immune system. Understanding how these cellular homologues enable the viruses to evade the antiviral defense and persist in the host for the lifetime will ultimatively lead also to a better understanding of the principle functions of the immune system. In this review we focused on cellular homologues encoded by human herpesviruses and discuss the functional consequences of their expression.

Herpes simplex virus type 2 UL34 protein requires UL31 protein for its relocation to the internal nuclear membrane in transfected cells

Herpes simplex virus type 2 UL34 protein is expressed late in infection and is required for envelopment of nucleocapsids at the nuclear membrane and possibly at the endoplasmic reticulum (ER). It is a type II membrane protein with a C-terminal anchor that localizes mainly to the nuclear membrane in infected cells. However, in single transient expression, UL34 protein localizes predominantly to the ER. Relocation of UL34 protein from the ER to the internal nuclear membrane and the nucleus was observed in the presence of UL31 protein, a phosphoprotein known to interact physically with UL34. It is suggested here that interaction with UL31 protein is important for the nuclear targetting of UL34 protein and also that the trans-membrane region of UL34 protein is responsible for its localization at the internal nuclear membrane. The results also suggest possible sites for the interaction.

Human herpesviruses 6 and 7 in solid organ transplant recipients

The impact of cytomegalovirus, a member of the beta-herpesvirus subgroup of the Herpesviridae, on patients who have undergone transplantation cannot be overstated. However, in the last 15 years, 2 additional members of the human beta-herpesvirus family have been discovered: human herpesviruses 6 and 7 (HHV-6 and HHV-7). The impact of HHV-6 and HHV-7 is assessed, as is the well-being of transplant recipients. Also discussed is whether the data on the pathological consequences of infection warrant routine screening for these viruses in solid organ transplant recipients.

Human herpesvirus 7 is latent in gastric mucosa

Chronic gastritis is associated frequently with persistent infection by Helicobacter pylori. However, not all patients with chronic gastritis have evidence of H. pylori infection, suggesting that other factors might contribute to the development of gastritis. The present study was undertaken to evaluate a possible etiologic role of human herpesvirus 7 (HHV-7). HHV-7 DNA was detected in about 80% of gastric biopsies, both in healthy mucosa from individuals without evidence of inflammation and in biopsies from patients with histologically confirmed chronic gastric inflammation. HHV-7 was present also in H. pylori negative samples, was associated specifically with gastric tissue and not with residual blood within the mucosa, and was present with high viral loads. HHV-7 DNA persisted in several patients also after remission of gastric inflammation and the viral presence did not correlate with specific symptoms. Analysis by RT-PCR showed that HHV-7 is transcriptionally inactive in chronic gastritis lesions. These observations show that gastric tissue represents a site of HHV-7 latent infection and a potential reservoir for viral reactivation.

Sequence requirements for interaction of human herpesvirus 7 origin binding protein with the origin of lytic replication

As do human herpesvirus 6 variants A and B (HHV-6A and -6B), HHV-7 encodes a homolog of the alphaherpesvirus origin binding protein (OBP), which binds at sites in the origin of lytic replication (oriLyt) to initiate DNA replication. In this study, we sought to characterize the interaction of the HHV-7 OBP (OBP(H7)) with its cognate sites in the 600-bp HHV-7 oriLyt. We expressed the carboxyl-terminal domain of OBP(H7) and found that amino acids 484 to 787 of OBP(H7) were sufficient for DNA binding activity by electrophoretic mobility shift analysis. OBP(H7) has one high-affinity binding site (OBP-2) located on one flank of an AT-rich spacer element and a low-affinity site (OBP-1) on the other. This is in contrast to the HHV-6B OBP (OBP(H6B)), which binds with similar affinity to its two cognate OBP sites in the HHV-6B oriLyt. The minimal recognition element of the OBP-2 site was mapped to a 14-bp sequence. The OBP(H7) consensus recognition sequence of the 9-bp core, BRTYCWCCT (where B is a T, G, or C; R is a G or A; Y is a T or C; and W is a T or A), overlaps with the OBP(H6B) consensus YGWYCWCCY and establishes YCWCC as the roseolovirus OBP core recognition sequence. Heteroduplex analysis suggests that OBP(H7) interacts along one face of the DNA helix, with the major groove, as do OBP(H6B) and herpes simplex virus type 1 OBP. Together, these results illustrate both conserved and divergent DNA binding properties between OBP(H7) and OBP(H6B).

Virally encoded 7TM receptors

A number of herpes- and poxviruses encode 7TM G-protein coupled receptors most of which clearly are derived from their host chemokine system as well as induce high expression of certain 7TM receptors in the infected cells. The receptors appear to be exploited by the virus for either immune evasion, cellular reprogramming, tissue targeting or for cell entry. Through their efficient evolutionary machinery and through in vivo selection performed directly on the human cellular and molecular targets, virus have been able to optimize the encoded receptors for distinct pharmacological profiles to help in various parts of the viral life cyclus. Most of the receptors encoded by human pathogenic virus are still orphan receptors, i.e. the endogenous ligand is unknown. In the few cases where it has been possible to characterize these receptors pharmacologically, they have been found to bind a broad spectrum of either CC chemokines, US28 from human cytomegalovirus, or CXC chemokines, ORF74 from human herpesvirus 8. Nevertheless, US28 has been specifically optimized for recognition of the membrane bound chemokine, fractalkine, conceivably involved in cell-cell transfer of virus; whereas ORF74 among the endogenous CXC chemokines has selected angiogenic chemokines as agonists and angiostatic/modulatory chemokines as inverse agonists. ORF74 possess substantial cell-transforming properties and signals with high constitutive activity through the phospholipase C and MAP kinase pathways. Interestingly, transgenic expression of this single gene in certain lymphocyte cell lineages leads to the development of lesions which are remarkably similar to Kaposi's sarcoma, a human herpesvirus 8 associated disease. Thus, this and other virally encoded 7TM receptors appear to be attractive future drug targets.

Murine cytomegalovirus M78 protein, a G protein-coupled receptor homologue, is a constituent of the virion and facilitates accumulation of immediate-early viral mRNA

The M78 protein of murine cytomegalovirus exhibits sequence features of a G protein-coupled receptor. It is synthesized with early kinetics, it becomes partially colocalized with Golgi markers, and it is incorporated into viral particles. We have constructed a viral substitution mutant, SMsubM78, which lacks most of the M78 ORF. The mutant produces a reduced yield in cultured 10.1 fibroblast and IC21 macrophage cell lines. The defect is multiplicity dependent and greater in the macrophage cell line. Consistent with its growth defect in cultured cells, the mutant exhibits reduced pathogenicity in mice, generating less infectious progeny than wild-type virus in all organs assayed. SMsubM78 fails to efficiently activate accumulation of the viral m123 immediate-early mRNA in infected macrophages. M78 facilitates the accumulation of the immediate-early mRNA in cycloheximide-treated cells, arguing that it acts in the absence of de novo protein synthesis. We conclude that the M78 G protein-coupled receptor homologue is delivered to cells as a constituent of the virion, and it acts to facilitate the accumulation of immediate-early mRNA.

Viral exploitation and subversion of the immune system through chemokine mimicry

The chemokine superfamily of leukocyte chemoattractants coordinates development and deployment of the immune system by signaling through a family of G protein-coupled receptors. The importance of this system to antimicrobial host defense has been supported by the discovery of numerous herpesviruses and poxviruses that encode chemokine mimics able to block chemokine action. However, specific herpesviruses and lentiviruses can also exploit the immune system through chemokine mimicry, for example, to facilitate viral dissemination or, as in the case of HIV-1, to directly infect leukocyte target cells. The study of viral mimicry of chemokines and chemokine receptors is providing important new concepts in viral immunopathogenesis, new anti-inflammatory drug leads and new targets and concepts for antiviral drug and vaccine development.

Murine cytomegalovirus open reading frame M27 plays an important role in growth and virulence in mice

Using a Tn3-based transposon mutagenesis approach, we have generated a pool of murine cytomegalovirus (MCMV) mutants. In this study, one of the mutants, RvM27, which contained the transposon sequence at open reading frame M27, was characterized both in tissue culture and in immunocompetent BALB/c mice and immunodeficient SCID mice. Our results suggest that the M27 carboxyl-terminal sequence is dispensable for viral replication in vitro. Compared to the wild-type strain and a rescued virus that restored the M27 region, RvM27 was attenuated in growth in both BALB/c and SCID mice that were intraperitoneally infected with the viruses. Specifically, the titers of RvM27 in the salivary glands, lungs, spleens, livers, and kidneys of the infected SCID mice at 21 days postinfection were 50- to 500-fold lower than those of the wild-type virus and the rescued virus. Moreover, the virulence of the mutant virus appeared to be attenuated, because no deaths occurred among SCID mice infected with RvM27 for up to 37 days postinfection, while all the animals infected with the wild-type and rescued viruses died within 27 days postinfection. Our observations provide the first direct evidence to suggest that a disruption of M27 expression results in reduced viral growth and attenuated viral virulence in vivo in infected animals. Moreover, these results suggest that M27 is a viral determinant required for optimal MCMV growth and virulence in vivo and provide insight into the functions of the M27 homologues found in other animal and human CMVs as well as in other betaherpesviruses.

Constitutive signaling of the human cytomegalovirus-encoded chemokine receptor US28

Previously it was shown that the HHV-8-encoded chemokine receptor ORF74 shows considerable agonist-independent, constitutive activity giving rise to oncogenic transformation (Arvanitakis, L., Geras-Raaka, E., Varma, A., Gershengorn, M. C., and Cesarman, E. (1997) Nature 385, 347-350). In this study we report that a second viral-encoded chemokine receptor, the human cytomegalovirus-encoded US28, also efficiently signals in an agonist-independent manner. Transient expression of US28 in COS-7 cells leads to the constitutive activation of phospholipase C and NF-kappaB signaling via G(q/11) protein-dependent pathways. Whereas phospholipase C activation is mediated via Galpha(q/11) subunits, the activation of NF-kappaB strongly depends on betagamma subunits with a preference for the beta(2)gamma(1) dimer. The CC chemokines RANTES (regulated on activation, normal T cell expressed and secreted) and MCP-1 (monocyte chemotactic protein-1) act as neutral antagonists at US28, whereas the CX(3)C chemokine fractalkine acts as a partial inverse agonist with IC(50) values of 1-5 nm. Our data suggest that a high level of constitutive activity might be a more general characteristic of viral G protein-coupled receptors and that human cytomegalovirus might exploit this G protein-coupled receptor property to modulate the homeostasis of infected cells via the early gene product US28.

The sequence and antiapoptotic functional domains of the human cytomegalovirus UL37 exon 1 immediate early protein are conserved in multiple primary strains

The human cytomegalovirus UL37 exon 1 gene encodes the immediate early protein pUL37x1 that has antiapoptotic and regulatory activities. Deletion mutagenesis analysis of the open reading frame of UL37x1 identified two domains that are necessary and sufficient for its antiapoptotic activity. These domains are confined within the segments between amino acids 5 to 34, and 118 to 147, respectively. The first domain provides the targeting of the protein to mitochondria. Direct PCR sequencing of UL37 exon 1 amplified from 26 primary strains of human cytomegalovirus demonstrated that the promoter, polyadenylation signal, and the two segments of pUL37x1 required for its antiapoptotic function were invariant in all sequenced strains and identical to those in AD169 pUL37x1. In total, UL37 exon 1 varies between 0.0 and 1.6% at the nucleotide level from strain AD169. Only 11 amino acids were found to vary in one or more viral strains, and these variations occurred only in the domains of pUL37x1 dispensable for its antiapoptotic function. We infer from this remarkable conservation of pUL37x1 in primary strains that this protein and, probably, its antiapoptotic function are required for productive replication of human cytomegalovirus in humans.

The UL34 gene product of herpes simplex virus type 2 is a tail-anchored type II membrane protein that is significant for virus envelopment

The UL34 gene of herpes simplex virus type 2 (HSV-2) is highly conserved in the herpesvirus family. The UL34 gene product was identified In lysates of HSV-2-infected cells as protein species with molecular masses of 31 and 32.5 kDa, the latter being a phosphorylated product. Synthesis of these proteins occurred at late times post-infection and was highly dependent on viral DNA synthesis. Immunofluorescence assays revealed that the UL34 protein was localized in the cytoplasm in a continuous net-like structure, closely resembling the staining pattern of the endoplasmic reticulum (ER), in both HSV-2-infected cells and in cells transiently expressing UL34 protein. Deletion mutant analysis showed that this colocalization required the C terminus of the UL34 protein. The UL34 protein associated with virions but not with A, B or C capsids. We treated virions, HSV-2-infected cells and cells expressing the UL34 protein with a protease in order to examine the topology of the UL34 protein. In addition, we constructed UL34 deletion mutant proteins and examined their intracellular localization. Our data strongly support the hypothesis that the UL34 protein is inserted into the viral envelope as a tail-anchored type II membrane protein and is significant for virus envelopment.

Evolutionary aspects of oncogenic herpesviruses

Several of the gamma-herpesviruses are known to have cellular transforming and oncogenic properties. The genomes of eight distinct gamma-herpesviruses have been sequenced, and the resulting database of information has enabled the identification of genetic similarities and differences between evolutionarily closely related and distant viruses of the subfamily and between the gamma-herpesviruses and other members of the herpesvirus family. The recognition of coincident loci of genetic divergence between individual gamma-herpesviruses and the identification of novel genes and cellular gene homologues in these genomic regions has delineated a subset of genes that are likely to contribute to the unique biological properties of these viruses. These genes, together with gamma-herpesvirus conserved genes not found in viruses outside the family, might be responsible for virus specific pathogenicity and pathogenic effects, such as viral associated neoplasia, characteristic of the subfamily. The presence of the gamma-herpesvirus major divergent genomic loci and the apparent increased mutational frequencies of homologous genes (where they occur) within these regions, indicates that these loci possess particular features that drive genetic divergence. Whatever the mechanisms underlying this phenomenon, it potentially provides the basis for the relatively rapid adaptation and evolution of gamma-herpesviruses and the diversity of biological and pathogenic properties.

Rat cytomegalovirus R89 is a highly conserved gene which expresses a spliced transcript

In all sequenced herpesvirus genomes, a homolog of the herpes simplex virus type 1 UL15 gene has been identified. This gene encodes a protein that is involved in viral genome maturation. Although transcription of the alphaherpesvirus UL15 gene has been analyzed in detail, not much is known about the expression of its betaherpesvirus homologs. We therefore set out to characterize transcription of the rat cytomegalovirus counterpart of UL15, R89. Here we report that R89 consists of two exons separated by a 4.7-kb intron. The spliced R89 transcript, which is expressed at late times postinfection (p.i.), has the capacity to encode a protein of 670 amino acids with a calculated molecular mass of 77.1 kDa. The predicted amino acid sequence of this protein is highly similar to that of the proteins predicted to be encoded by the human cytomegalovirus UL89 and murine cytomegalovirus M89 genes (64.3 and 84.5% overall identity, respectively). The region between R89 exon 1 and exon 2 was found to contain five additional genes, r90, R91, R92, R93 and R94, the latter two of which are conserved among all herpesviruses. We show that these genes are transcribed in a highly complex fashion, resulting in numerous mono- and polycistronic mRNAs.

Proportion positive for Epstein-Barr virus, cytomegalovirus, human herpesvirus 6, Toxoplasma, and human immunodeficiency virus types 1 and 2 in heterophile-negative patients with an absolute lymphocytosis or an instrument-generated atypical lymphocyte flag

OBJECTIVES

To determine the proportion of patients with evidence of an acute infection due to Epstein-Barr virus (EBV), cytomegalovirus (CMV), human herpesvirus 6 (HHV-6), Toxoplasma, or human immunodeficiency virus types 1 and 2 (HIV-1 and HIV-2) in heterophile-negative patients with an absolute lymphocytosis or an instrument-generated atypical lymphocyte flag, and to develop a cost-effective testing algorithm for managing such heterophile-negative patients.

DESIGN

We conducted a prospective investigation of 70 selected outpatients who tested negative for heterophile antibody in association with an absolute lymphocytosis or instrument-generated atypical lymphocyte flag. The control population consisted of 50 patients who were heterophile negative and had a normal absolute lymphocyte count and no instrument-generated atypical lymphocyte flag.

SETTING

A large outpatient laboratory system.

INTERVENTION

Viral serology for HHV-6 was performed by immunofluorescence, and all other serologies were performed by enzyme-linked immunoassay. All testing was for immunoglobulin (Ig) M antibodies, except in the case of HIV.

RESULTS

The proportion of study patients positive for EBV was 40% (28/70); for CMV, 39% (27/70); for HHV-6, 25% (16/65); for Toxoplasma, 3% (2/70); and for HIV, 0% (0/70). All 50 control patients were negative for EBV IgM antibodies. When patients with more than 1 positive viral test were excluded from analysis, positivity was 20% (9/45) for EBV, 22% (10/45) for CMV, 9% (4/45) for HHV-6, and 2% (1/45) for Toxoplasma. Utilizing hypothesis-generating logistic regression models, Downey type II atypical lymphocytes were significantly associated with EBV positivity (P =.006), while Downey type III lymphocytes were significantly associated with HHV-6 positivity (P =.016), and there was a trend for the association of Downey type I lymphocytes with CMV positivity (P =.097).

CONCLUSIONS

A positive viral serology was identified in 70% of study patients. Multiple positive serologies complicate establishing a definitive diagnosis. Potential cost savings may be associated with the use of an appropriate testing algorithm.

Functional interaction between pleiotropic transactivator pUL69 of human cytomegalovirus and the human homolog of yeast chromatin regulatory protein SPT6

The phosphoprotein pUL69 of human cytomegalovirus (HCMV), which is a herpesvirus of considerable medical importance in immunosuppressed patients and newborns, has previously been identified as an early-late viral protein that can stimulate several viral and cellular promoters and thus exerts a rather broad activation pattern. To gain insight into the mechanism of this transactivation process, we looked for cellular factors interacting with pUL69 in a yeast two-hybrid screen. Using a B-lymphocyte cDNA library fused to the GAL4 activation domain, we identified 34 clones, 11 of which comprised one distinct gene. Interaction with this gene turned out to be very strong, producing beta-galactosidase levels 100-fold greater than the background as measured in an ONPG (o-nitrophenyl-beta-D-galactopyranoside) assay. Sequencing identified this gene as the human homolog of the yeast factor SPT6, which is thought to be involved in the regulation of chromatin structure. A direct interaction of pUL69 and the carboxy terminus of hSPT6 could be demonstrated using in vitro pull-down experiments. After having generated a specific antiserum that is able to detect the endogenous hSPT6 protein, we were able to observe an in vivo interaction of both proteins by coimmunoprecipitation analysis. The interaction domain within pUL69 was mapped to a central domain of this viral protein that is conserved within the homologous proteins of other herpesviruses such as the ICP27 protein of herpes simplex virus. Internal deletions within this central domain, as well as a single amino acid exchange at position C495, resulted in a loss of interaction. This correlated with a loss of the transactivation potential of the respective mutants, suggesting that the hSPT6 interaction of pUL69 is essential for stimulating gene expression. Furthermore, we demonstrate that the carboxy terminus of hSPT6 also binds to histon H3 and that this interaction can be antagonized by pUL69. This allows the deduction of a model by which pUL69 acts as an antirepressor by competing for binding of histones to hSPT6, thereby antagonizing the chromatin remodeling function of this cellular protein.

The conserved carboxyl-terminal half of herpes simplex virus type 1 regulatory protein ICP27 is dispensable for viral growth in the presence of compensatory mutations

ICP27 is an essential herpes simplex virus type 1 (HSV-1) immediate-early protein that regulates viral gene expression by poorly characterized mechanisms. Previous data suggest that its carboxyl (C)-terminal portion is absolutely required for productive viral infection. In this study, we isolated M16R, a second-site revertant of a viral ICP27 C-terminal mutant. M16R harbors an intragenic reversion, as demonstrated by the fact that its cloned ICP27 allele can complement the growth of an HSV-1 ICP27 deletion mutant. DNA sequencing demonstrated that the intragenic reversion is a frameshift alteration in a homopolymeric run of C residues at codons 215 to 217. This results in the predicted expression of a truncated, 289-residue molecule bearing 72 novel C-terminal residues derived from the +1 reading frame. Consistent with this, M16R expresses an ICP27-related molecule of the predicted size in the nuclei of infected cells. Transfection-based viral complementation assays confirmed that the truncated, frameshifted protein can partially substitute for ICP27 in the context of viral infection. Surprisingly, its novel C-terminal residues are required for this activity. To see if the frameshift mutation is all that is required for M16R's viability, we re-engineered the M16R ICP27 allele and inserted it into a new viral background, creating the HSV-1 mutant M16exC. An additional mutant, exCd305, was constructed which possesses the frameshift in the context of an ICP27 gene with the C terminus deleted. We found that both M16exC and exCd305 are nonviable in Vero cells, suggesting that one or more extragenic mutations are also required for the viability of M16R. Consistent with this interpretation, we isolated two viable derivatives of exCd305 which grow productively in Vero cells despite being incapable of encoding the C-terminal portion of ICP27. Studies of viral DNA synthesis in mutant-infected cells indicated that the truncated, frameshifted ICP27 protein can enhance viral DNA replication. In summary, our results demonstrate that the C-terminal portion of ICP27, conserved widely in herpesviruses and previously believed to be absolutely essential, is dispensable for HSV-1 lytic replication in the presence of compensatory genomic mutations.

Lymphoid/neuronal cell surface OX2 glycoprotein recognizes a novel receptor on macrophages implicated in the control of their function

The OX2 membrane glycoprotein (CD200) is expressed on a broad range of tissues including lymphoid cells, neurons, and endothelium. We report the characterization of an OX2 receptor (OX2R) that is a novel protein restricted to cells of the myeloid lineage. OX2 and its receptor are both cell surface glycoproteins containing two immunoglobulin-like domains and interact with a dissociation constant of 2.5 microM and koff 0.8 s(-1), typical of many leukocyte protein membrane interactions. Pervanandate treatment of macrophages showed that OX2R could be phosphorylated on tyrosine residues. Blockade of the OX2-OX2R interaction with an OX2R mAb exacerbated the disease model experimental allergic encephalomyelitis. These data, together with data from an OX2-deficient mouse (R. M. Hoek et al., submitted), suggest that myeloid function can be controlled in a tissue-specific manner by the OX2-OX2R interaction.

Detection of Epstein-Barr virus and human herpesvirus 7 and 8 genomes in primary cutaneous T- and B-cell lymphomas

BACKGROUND

Several studies have investigated the possible involvement of viral agents, particularly herpesviruses, in primary cutaneous lymphoma (PCL).

OBJECTIVES

Our aim was to screen for the presence of human herpesvirus 7 (HHV-7) and 8 (HHV-8) genomes in samples of PCL, and to determine if their presence was independent of Epstein-Barr virus (EBV).

METHODS

Screening was performed using polymerase chain reaction assay in 64 skin samples from historical lesional tissues with PCL.

RESULTS

Only nine cases showed positivity for HHV-7: four of 29 mycosis fungoides (MF), two of four CD30-positive large-cell cutaneous T-cell lymphoma (CTCL), two of 12 follicle centre cutaneous B-cell lymphoma (CBCL) and one of nine marginal zone CBCL. Fifteen cases tested positive for EBV: seven of 29 MF, two of four pleomorphic small/medium sized CTCL, three of three angiocentric CTCL, one of 12 follicle centre CBCL and two of nine marginal zone CBCL. All cases were uniformly negative for HHV-8. No simultaneous positivity was found for EBV and HHV-7. Controls tested negative for all viruses.

CONCLUSIONS

The findings indicate that EBV, HHV-7 and HHV-8 seem not to be involved in the pathogenesis of PCL.

Complete DNA sequence of the rat cytomegalovirus genome

We have determined the complete genome sequence of the Maastricht strain of rat cytomegalovirus (RCMV). The RCMV genome has a length of 229,896 bp and is arranged as a single unique sequence flanked by 504-bp terminal direct repeats. RCMV was found to have counterparts of all but one of the open reading frames (ORFs) that are conserved between murine CMV (MCMV) and human CMV (HCMV). Like HCMV, RCMV lacks homologs of the genes belonging to the MCMV m02 glycoprotein gene family. However, RCMV contains 15 ORFs with homology to members of the MCMV m145 glycoprotein gene family. Four ORFs are predicted to encode homologs of host proteins; R33 and R78 both putatively encode G protein-coupled receptors, whereas r144 and r131 encode homologs of major histocompatibility class I heavy chains and CC chemokines, respectively. An intriguing feature of the RCMV genome is the presence of an ORF, r127, with similarity to the rep gene of parvoviruses as well as ORF U94 of human herpesvirus 6A (HHV-6A) and HHV-6B. Counterparts of these ORFs have not been found in the other sequenced herpesviruses.

Characterization of human herpesvirus 7 U27 gene product and identification of its nuclear localization signal

A monoclonal antibody, 5H4, that recognizes human herpesvirus 7 (HHV-7) was used in Western analysis to probe HHV-7-infected SupT1 cells. This antibody recognizes a 40-kDa virus-specific polypeptide that is expressed in the absence of viral DNA synthesis. By screening a lambdagt11 HHV-7 cDNA library, the gene encoding the protein was identified as the U27 open reading frame previously reported [J. Virol. (1996) 70, 5975-5989]. Immunofluorescent studies showed a punctate nuclear localization of the protein in both HHV-7-infected cells and transfected cells. A computer program predicted two classic nuclear localization signals (NLSs) in the middle and C-terminal regions of the protein. A C-terminal deletion mutant of the protein could not enter the nucleus, whereas green fluorescent protein or maltose binding protein fused to the C-terminal region of the protein was transported into the nucleus. These findings demonstrate that the predicted C-terminal, but not middle, NLS of the protein actually function as NLS. In addition, nuclear transport of a maltose binding protein-fusion protein containing the C-terminal NLS of the U27 protein was inhibited by both wheat germ agglutinin and a Q69L Ran-GTP mutant, indicating that the U27 protein is transported into the nucleus from the cytoplasm by means of classic nuclear transport machinery. Interestingly, this NLS motif is highly conserved at the C-termini of all herpesvirus DNA polymerase processivity factors that have been examined.

Infection of CD34+ hematopoietic progenitor cells by human herpesvirus 7 (HHV-7)

To investigate the tropism of the T-lymphotropic human herpesvirus 7 (HHV-7) for hematopoietic progenitors, cord blood CD34+ cells were inoculated in vitro with HHV-7 and then induced to differentiate along the granulocytic and erythroid lineages by the addition of appropriate cytokine cocktails. In semisolid assays, HHV-7 modestly affected the growth of committed (granulocytic/macrophagic and erythroid) progenitors, whereas it significantly decreased the number of pluripotent (granulocytic/erythroid/ monocytic/megakaryocytic) progenitors. Such inhibitory effect was completely abrogated by incubating HHV-7 inoculum with anti–HHV-7 neutralizing serum. In liquid cultures, HHV-7 hastened maturation along the myeloid but not the erythroid lineage, as demonstrated by the up-regulation of CD33 early myeloid antigen at day 7 of culture, and of CD15 and CD14 antigens at day 15. Moreover, HHV-7 messenger RNA was detected by reverse transcriptase–polymerase chain reaction (RT-PCR) in cells maturating along both the myeloid and the erythroid lineages. To evaluate the relevance of these in vitro findings, the presence of HHV-7 was investigated in bone marrow (BM) unfractionated mononuclear cells (MCs) as well as in purified CD34+ and CD34− cell subsets, obtained from 14 normal adult donors. HHV-7 DNA was detected by DNA-PCR in 4 of 7 BMMC samples, and it was found to be associated with both the CD34− (2 of 7) and the CD34+ (1 of 7) fractions. These data indicate that HHV-7 infects BM cells in vivo and shows the ability to affect the survival/differentiation of CD34+ hematopoietic progenitors in vitro by inhibiting more ancestral progenitors and perturbing the maturation of myeloid cells.

Infection of CD34+ hematopoietic progenitor cells by human herpesvirus 7 (HHV-7)

To investigate the tropism of the T-lymphotropic human herpesvirus 7 (HHV-7) for hematopoietic progenitors, cord blood CD34+ cells were inoculated in vitro with HHV-7 and then induced to differentiate along the granulocytic and erythroid lineages by the addition of appropriate cytokine cocktails. In semisolid assays, HHV-7 modestly affected the growth of committed (granulocytic/macrophagic and erythroid) progenitors, whereas it significantly decreased the number of pluripotent (granulocytic/erythroid/ monocytic/megakaryocytic) progenitors. Such inhibitory effect was completely abrogated by incubating HHV-7 inoculum with anti–HHV-7 neutralizing serum. In liquid cultures, HHV-7 hastened maturation along the myeloid but not the erythroid lineage, as demonstrated by the up-regulation of CD33 early myeloid antigen at day 7 of culture, and of CD15 and CD14 antigens at day 15. Moreover, HHV-7 messenger RNA was detected by reverse transcriptase–polymerase chain reaction (RT-PCR) in cells maturating along both the myeloid and the erythroid lineages. To evaluate the relevance of these in vitro findings, the presence of HHV-7 was investigated in bone marrow (BM) unfractionated mononuclear cells (MCs) as well as in purified CD34+ and CD34− cell subsets, obtained from 14 normal adult donors. HHV-7 DNA was detected by DNA-PCR in 4 of 7 BMMC samples, and it was found to be associated with both the CD34− (2 of 7) and the CD34+ (1 of 7) fractions. These data indicate that HHV-7 infects BM cells in vivo and shows the ability to affect the survival/differentiation of CD34+ hematopoietic progenitors in vitro by inhibiting more ancestral progenitors and perturbing the maturation of myeloid cells.

Structure of transcripts and proteins encoded by U79-80 of human herpesvirus 6 and its subcellular localization in infected cells

We analyzed the U79-80 gene of human herpesvirus 6 (HHV-6), which is predicted to be a positional homolog of the UL112-113 gene of human cytomegalovirus (HCMV). The U79-80 gene encoded a family of nuclear proteins of 36, 41, 44, and 59 kDa. These proteins had common amino termini and were generated by complex alternative splicing. Transcripts from U79-80 appeared as early as 3 h postinfection and could be detected in the presence of phosphonoformate. U79-80 proteins were seen as early as 8 h postinfection and could be detected in the presence of phosphonoformate but not in the presence of cycloheximide combined with actinomycin D treatment. The U79-80 proteins were localized to the nucleus of infected cells, where they were detected as a speckled or punctuate pattern. Moreover, the U79-80 proteins colocalized with the components of the viral DNA replication machinery and appeared to distribute adjacent to or touching nuclear domain 10, where viral DNA replication occurs. From the sequence analysis of genomic DNA, the predicted amino acid similarity between U79-80 and UL112-113 was lower than between other genes, but the characteristics of the transcripts and proteins encoded by U79-80 were similar to those of UL112-113. These results suggest that the U79-80 proteins have a role in viral DNA replication and are functional homologues of the UL112-113 proteins.

Monitoring of human herpesvirus-6 and -7 genomes in saliva samples of healthy adults by competitive quantitative PCR

Human herpesviruses-6 and -7 (HHV-6 and HHV-7) are thought to be transmitted during early infancy through saliva. However, the kinetics of the virus shedding in saliva of healthy adults, from whom children are assumed to acquire the viruses, is mostly unknown. This study was conducted to determine how many copies of the genome are secreted in saliva of healthy adults and to clarify the relationship between viral DNA load and virus isolation of HHV-6 and HHV-7. Competitive PCR was performed using primer sets in the U42 gene of each viral genome. In saliva samples from 29 healthy adults, HHV-6 and HHV-7 DNA was detected in 41.4% and 89.7%, respectively. The average copy number of the HHV-7 genome in the positive samples was higher than that of the HHV-6 genome. Follow-up studies of six seropositive individuals for 3 months showed that the amount of HHV-7 DNA was constant in each individual and that "high producers" and "low producers" could be distinguished. By contrast, the amount of HHV-6 DNA varied drastically over time in each individual. Although HHV-6 was never isolated from the saliva of any of the six individuals during the follow-up period, HHV-7 was isolated from each individual several times. The amount of HHV-7 DNA tended to be higher at the times when the virus was isolated than at the times when the virus was not isolated. These data demonstrate a striking contrast between HHV-6 and HHV-7 in the kinetics of genome and virus shedding.

Identification and analysis of a novel heparin-binding glycoprotein encoded by human herpesvirus 7

Human herpesvirus 6 (HHV-6) and HHV-7 are closely related betaherpesviruses that encode a number of genes with no known counterparts in other herpesviruses. The product of one such gene is the HHV-6 glycoprotein gp82-105, which is a major virion component and a target for neutralizing antibodies. A 1.7-kb cDNA clone from HHV-7 was identified which contains a large open reading frame capable of encoding a predicted primary translational product of 468 amino acids (54 kDa) with 13 cysteine residues and 9 potential N-linked glycosylation sites. This putative protein, which we have termed gp65, was homologous to HHV-6 gp105 (30% identity) and contained a single potential membrane-spanning domain located near its amino terminus. Comparison of the cDNA sequence with that of the viral genome revealed that the gene encoding gp65 contains eight exons, spanning almost 6 kb of the viral genome at the right (3') end of the HHV-7 genome. Northern (RNA) blot analysis with poly(A)(+) RNA from HHV-7-infected cells revealed that the cDNA insert hybridized to a single major RNA species of 1.7 kb. Antiserum raised against a purified, recombinant form of gp65 recognized a protein of roughly 65 kDa in sucrose density gradient-purified HHV-7 preparations; treatment with PNGase F reduced this glycoprotein to a putative precursor of approximately 50 kDa. Gp65-specific antiserum also neutralized the infectivity of HHV-7, while matched preimmune serum did not do so. Finally, analysis of the biochemical properties of recombinant gp65 revealed a specific interaction with heparin and heparan sulfate proteoglycans and not with closely related molecules such as N-acetylheparin and de-N-sulfated heparin. At least two domains of the protein were found to contribute to heparin binding. Taken together, these findings suggest that HHV-7 gp65 may contribute to viral attachment to cell surface proteoglycans.

HHV-6, 7 and their related diseases

Human herpesvirus 6 (HHV-6) and human herpesvirus 7 (HHV-7) are relatively recently discovered beta-herpesvirus. They are prevalent in the human population. Primary infection of HHV-6 has been associated with exanthem subitum and febrile illness. Little information is known about the clinical characteristics of primary infection with HHV-7, although some cases of exanthem subitum have been linked to it. HHV-6 has been recently recognized as an opportunistic pathogen in patients with HIV infection and in transplant recipients. The techniques now available to detect these two viruses remain limited, though putative roles for HHV-6 and HHV-7 in several diseases linked to viral infection have been reported. This report reviews the current knowledge of HHV-6 and HHV-7 biology and their pathogenesis.

RANTES binding and down-regulation by a novel human herpesvirus-6 beta chemokine receptor

The human herpesvirus 6 (HHV-6) U51 gene defines a new family of betaherpesvirus-specific genes encoding multiple transmembrane glycoproteins with similarity to G protein-coupled receptors, in particular, human chemokine receptors. These are distinct from the HHV-6 U12 and HCMV US28 family. In vitro transcription and translation as well as transient cellular expression of U51 showed properties of a multiple transmembrane protein with a 30-kDa monomer as well as high m.w. aggregates or oligomers. Transient cellularly expressed U51 also appeared to form dimeric intermediates. Despite having only limited sequence similarity to chemokine receptors, U51 stably expressed in cell lines showed specific binding of the CC chemokine RANTES and competitive binding with other beta chemokines, such as eotaxin; monocyte chemoattractant protein 1, 3, and 4; as well as the HHV-8 chemokine vMIPII. In epithelial cells already secreting RANTES, U51 expression resulted in specific transcriptional down-regulation. This correlated with reduced secretion of RANTES protein into the culture supernatants. Regulation of RANTES levels may alter selective recruitment of circulating inflammatory cells that the virus can infect and thus could mediate the systemic spread of the virus from initial sites of infection in epithelia. Alternatively, chemokine regulation could modulate a protective inflammatory response to aid the spread of virus by immune evasion. Such mimicry, by viral proteins, of host receptors leading to down-regulation of chemokine expression is a novel immunomodulatory mechanism.

Modulating chemokines: more lessons from viruses

Chemokines are crucial effector molecules involved in orchestrating the host inflammatory response against invading pathogens. Viruses have devised several strategies for exploiting or neutralizing chemokines or their receptors to further their own propagation or elude host defenses. Insight into strategies used by viruses to modulate chemokines might help generate novel approaches for treating viral diseases and chemokine-mediated inflammatory disorders.

A highly selective CC chemokine receptor (CCR)8 antagonist encoded by the poxvirus molluscum contagiosum

The MC148 CC chemokine from the human poxvirus molluscum contagiosum (MCV) was probed in parallel with viral macrophage inflammatory protein (vMIP)-II encoded by human herpesvirus 8 (HHV8) in 16 classified human chemokine receptors. In competition binding using radiolabeled endogenous chemokines as well as radiolabeled MC148, MC148 bound with high affinity only to CCR8. In calcium mobilization assays, MC148 had no effect on its own on any of the chemokine receptors, but in a dose-dependent manner blocked the stimulatory effect of the endogenous I-309 chemokine on CCR8 without affecting chemokine-induced signaling of any other receptor. In contrast, vMIP-II acted as an antagonist on 10 of the 16 chemokine receptors, covering all four classes: XCR, CCR, CXCR, and CX(3)CR. In chemotaxis assays, MC148 specifically blocked the I-309-induced response but, for example, not stromal cell-derived factor 1alpha, monocyte chemoattractant protein 1, or interleukin 8-induced chemotaxis. We thus concluded that the two viruses choose two different ways to block the chemokine system: HHV8 encodes the broad-spectrum chemokine antagonist vMIP-II, whereas MCV encodes a highly selective CCR8 antagonist, MC148, conceivably to interfere with monocyte invasion and dendritic cell function. Because of its pharmacological selectivity, the MC148 protein could be a useful tool in the delineation of the role played by CCR8 and its endogenous ligand, I-309.

Development of Recombinant Diagnostic Reagents Based on pp85(U14) and p86(U11) Proteins To Detect the Human Immune Response to Human Herpesvirus 7 Infection

Human antibodies raised in response to human herpesvirus 7 (HHV-7) infection are directed predominantly to one or more HHV-7-infected cell proteins with apparent molecular masses of about 85 to 89 kDa. The genes that encode these proteins are unknown. However, several HHH-7 genes that possibly encode proteins in this molecular mass range have been identified. Thus, the proteins encoded by open reading frame U14 (85 kDa) and U11 (86 kDa) were expressed as recombinant proteins in bacteria. Of 13 human serum specimens that recognized the 85- to 89-kDa protein(s) of HHV-7-infected cells by immunoblotting, 12 were also reactive with recombinant pp85(U14) and 8 were reactive with p86(U11). It is concluded that (i) the HHV-7 immunodominant protein is pp85(U14) and (ii) the lack of posttranslational modifications in procaryotically expressed pp85 does not adversely affect the reactivity of human sera. Monoclonal antibody (MAb) 5E1 is an HHV-7-specific MAb directed to pp85(U14). Here, the HHV-7-specific epitope in pp85(U14) was finely mapped to the C′ terminal region between amino acid residues 484 and 502. However, as indicated by the low level of reactivity of human sera with the HHV-7-specific epitope recognized by MAb 5E1, human sera recognize additional epitopes of pp85(U14) that are required for their full reactivity.

Preferential associations of alleles of three distinct genes argue for the existence of two prototype variants of human herpesvirus 7

We had previously described six distinct alleles of the glycoprotein B (gB) gene of human herpesvirus 7 (HHV-7). The genetic changes corresponding to these alleles did not affect gB gene transcription or translation in in vitro assays. The study of distinct HHV-7-positive human samples showed preferential associations of some gB alleles with some alleles of two other genes, distantly located on the HHV-7 genome, coding for the phosphoprotein p100 (p100) and the major capsid protein (MCP). Two allele combinations, corresponding to 44 and 31% of the samples studied, respectively, were interpreted as the genetic signatures of two major prototype HHV-7 variants.

The U28 ORF of human herpesvirus-7 does not encode a functional ribonucleotide reductase R1 subunit

Herpesvirus ribonucleotide reductases, essential for the de novo synthesis of viral DNA, are composed of two non-identical subunits, termed R1 and R2. The U28 ORF from human herpesvirus-7 has been classified, by sequence comparisons, as a homologue of the R1 subunit from ribonucleotide reductase but no R2 ORF is present. Detailed analysis of the U28 amino acid sequence indicated that a number of essential R1 catalytic residues are absent. Cloning and expression of the U28 protein in E. coli and its subsequent characterization in subunit interaction and enzyme activity assays confirmed that it is not a functional equivalent of a herpesvirus R1. In the absence of the R2 gene, we propose that the R1 ORF has evolved a distinct, as yet unidentified, function not only in human herpesvirus-7 but also in other human betaherpes-viruses.

The rat cytomegalovirus R32 gene encodes a virion-associated protein that elicits a strong humoral immune response in infected rats

A gene of rat cytomegalovirus (RCMV), designated R32, has been identified that encodes a homologue of the human cytomegalovirus (HCMV) pp150 (ppUL32) major tegument phosphoprotein. The R32 ORF has the capacity to encode a 667 amino acid polypeptide (pR32) with a calculated molecular mass of 73 kDa. The predicted amino acid sequence of pR32 shows similarity to that of polypeptides predicted to be encoded by the HCMV UL32, murine cytomegalovirus M32 and human herpesvirus types 6 and 7 U11 genes. The R32 gene is transcribed as a 2.5 kb mRNA during the late phase of RCMV infection in rat embryo fibroblasts in vitro. To study expression of the pR32 protein in vitro and in vivo, a rabbit polyclonal antiserum was raised against a recombinant protein that comprised amino acids 252-522 of pR32. By using this antiserum, pR32 could be detected predominantly in the cytoplasm of RCMV-infected fibroblasts at 24 and 48 h post-infection in vitro. The pR32 protein was also detected within virions isolated from the culture medium of RCMV-infected cells. Expression of pR32 in vivo was observed within the cytoplasm of salivary gland epithelial cells of RCMV-infected rats. In addition, recombinant pR32 was found to react with sera from rats that were previously infected with RCMV, whereas reactivity was not seen with sera from mock-infected rats. Together, these findings indicate that RCMV pR32 represents the homologue of HCMV ppUL32, both in primary structure and in function.

Human herpesvirus 6B genome sequence: coding content and comparison with human herpesvirus 6A

Human herpesvirus 6 variants A and B (HHV-6A and HHV-6B) are closely related viruses that can be readily distinguished by comparison of restriction endonuclease profiles and nucleotide sequences. The viruses are similar with respect to genomic and genetic organization, and their genomes cross-hybridize extensively, but they differ in biological and epidemiologic features. Differences include infectivity of T-cell lines, patterns of reactivity with monoclonal antibodies, and disease associations. Here we report the complete genome sequence of HHV-6B strain Z29 [HHV-6B(Z29)], describe its genetic content, and present an analysis of the relationships between HHV-6A and HHV-6B. As sequenced, the HHV-6B(Z29) genome is 162,114 bp long and is composed of a 144,528-bp unique segment (U) bracketed by 8,793-bp direct repeats (DR). The genomic sequence allows prediction of a total of 119 unique open reading frames (ORFs), 9 of which are present only in HHV-6B. Splicing is predicted in 11 genes, resulting in the 119 ORFs composing 97 unique genes. The overall nucleotide sequence identity between HHV-6A and HHV-6B is 90%. The most divergent regions are DR and the right end of U, spanning ORFs U86 to U100. These regions have 85 and 72% nucleotide sequence identity, respectively. The amino acid sequences of 13 of the 17 ORFs at the right end of U differ by more than 10%, with the notable exception of U94, the adeno-associated virus type 2 rep homolog, which differs by only 2.4%. This region also includes putative cis-acting sequences that are likely to be involved in transcriptional regulation of the major immediate-early locus. The catalog of variant-specific genetic differences resulting from our comparison of the genome sequences adds support to previous data indicating that HHV-6A and HHV-6B are distinct herpesvirus species.

Comparison of the complete DNA sequences of human herpesvirus 6 variants A and B

Human herpesvirus 6 (HHV-6), which belongs to the betaherpesvirus subfamily and infects mainly T cells in vitro, causes acute and latent infections. Two variants of HHV-6 have been distinguished on the basis of differences in several properties. We have determined the complete DNA sequence of HHV-6 variant B (HHV-6B) strain HST, the causative agent of exanthem subitum, and compared the sequence with that of variant A strain U1102. A total of 115 potential open reading frames (ORFs) were identified within the 161,573-bp contiguous sequence of the entire HHV-6 genome, including some genes with remarkable differences in amino acid identity. All genes with <70% identity between the two variants were found to contain deleted regions when ORFs that could not be expressed were excluded from the comparison. Except in the case of U47, these differences were found in immediate-early/regulatory genes, DR2, DR7, U86/90, U89/90, and U95, which may represent characteristic differences of variants A and B. Also, we have successfully typed 14 different strains belonging to variant A or B by PCR using variant-specific primers; the results suggest that the remarkable differences observed were conserved evolutionarily as variant-specific divergence.

Temporal mapping of transcripts in human herpesvirus-7

Transcription of human herpesvirus-7 (HHV-7) in cultures of productively infected T-cells was studied. Transcription of HHV-7 was regulated by the typical herpesvirus cascade in which alpha, beta and gamma genes are sequentially transcribed. Transcripts of U10, U14, U18, U31, U39, U41, U42, U53, U73 and U89/90 were detected 3 h after infection and were not inhibited by the absence of protein synthesis and therefore were alpha functions. U19 and U18/20 were beta genes; their transcription was inhibited by cycloheximide but not by phosphonoacetate, an inhibitor of DNA synthesis. U60/66 and U98/100 were gamma genes since their spliced transcripts were not detected in cells treated with phosphonoacetate. HHV-7 transcription was regulated by complex mechanisms, which involve the temporal coordinated activation of specific viral promoters and post-transcriptional processing. Splice mechanisms were also temporally regulated. Transcription of U89/90 pre-mRNA and splice took place simultaneously in the immediate-early phase. On the other hand, U16/17 pre-mRNA was synthesized with typical alpha kinetics, but the spliced product was regulated as a beta function. Likewise, the primary transcripts of U60/66 and U98/100 were alpha and beta, respectively, but both spliced products were synthesized in the late phase of virus replication. Finally, HHV-7 supported a bona fide latent infection in the adult population, since viral transcripts were not detected in peripheral blood mononuclear cells of healthy donors infected with HHV-7.

The murine cytomegalovirus M25 open reading frame encodes a component of the tegument

The murine cytomegalovirus (MCMV) monoclonal antibody 5C7:6 was used in Western analysis to probe MCMV infected murine embryo cells (MEC). This antibody recognizes three virus specific polypeptides of 130, 105, and 95 kDa and pulse-chase experiments demonstrated that these three proteins, although antigenically related, are distinct. The 105- and 95-kDa species were expressed with early kinetics, whereas the 130-kDa protein was synthesized as a true late. By screening a lambdagt11 MCMV cDNA library, the gene encoding these proteins was identified as the M25 open reading frame previously reported by Dallas et al. (Dallas, P. B., Lyons, P. A., Hudson, J. B., Scalzo, A. A., and Shellam, G. R., 1994, Virology 200, 643-650). Immunofluorescent studies monitored the location of pM25, present in the nucleus at 15 h after infection, condensing around the periphery of the nucleus at 18 h, before finally accumulating in the cytoplasm. Immunoelectron microscopy detected gold particles associated with the viral tegument of enveloped virions located in the cytoplasm and extracellular space but not with naked nucleocapsids. Western analysis of MCMV purified virions depicted the presence of the 130-kDa protein, the predominant M25 species, in mature virus particles. Together these findings provide compelling evidence that the 130-kDa M25 polypeptide is a component of the viral tegument.

Novel, nonconsensus cellular splicing regulates expression of a gene encoding a chemokine-like protein that shows high variation and is specific for human herpesvirus 6

There are few genes that are specific and diagnostic for human herpesvirus-6. U83 and U22 are two of them. U22 is unique, whereas U83 encodes distant similarity with some cellular chemokines. Reverse transcription-polymerase chain reaction, cDNA cloning, and sequence analyses show polyadenylated RNA transcripts corresponding to minor full-length and abundant spliced forms of U83 in human herpesvirus 6-infected cells. The splice donor and acceptor sites do not fit consensus sequences for either major GT-AG or minor AT-AC introns. However, the spliced form can also be detected in a U83 transfected cell line; thus the novel sites are used by cellular mechanisms. This intron may represent a new minor CT-AC splicing class. The novel splicing regulates gene expression by introducing a central stop codon that abrogates production of the chemokine-like molecule, resulting in an encoded truncated peptide. The use of metabolic inhibitors and an infection time course showed expression of the two RNA transcripts with immediate early kinetics. However, the full-length product accumulated later, dependent on virus DNA replication, similar to U22. Sequence analyses of 16 strains showed high variation (13%) in U83, with conservation of the novel splice sites. Representative strain variants had similar kinetics of expression and spliced products.

Inhibition of Epstein-Barr virus replication by a benzimidazole L-riboside: novel antiviral mechanism of 5, 6-dichloro-2-(isopropylamino)-1-beta-L-ribofuranosyl-1H-benzimidazole

Although a number of antiviral drugs inhibit replication of Epstein-Barr virus (EBV) in cell culture, and acyclovir (ACV) suppresses replication in vivo, currently available drugs have not proven effective for treatment of EBV-associated diseases other than oral hairy leukoplakia. Benzimidazole riboside compounds represent a new class of antiviral compounds that are potent inhibitors of human cytomegalovirus (HCMV) replication but not of other herpesviruses. Here we characterize the effects of two compounds in this class against lytic replication of EBV induced in a Burkitt lymphoma cell line latently infected with EBV. We analyzed linear forms of EBV genomes, indicative of lytic replication, and episomal forms present in latently infected cells by terminal probe analysis followed by Southern blot hybridization as well as the high-molecular-weight unprocessed viral DNA by pulsed-field gel electrophoresis. D-Ribofuranosyl benzimidazole compounds that act as inhibitors of HCMV DNA maturation, including BDCRB (5, 6-dichloro-2-bromo-1-beta-D-ribofuranosyl-1H-benzimidazole), did not affect the accumulation of high-molecular-weight or monomeric forms of EBV DNA in the induced cells. In contrast, the generation of linear EBV DNA as well as precursor viral DNA was sensitive to the L-riboside 1263W94 [5, 6-dichloro-2-(isopropylamino)-1-beta-L-ribofuranosyl-1H-benzimidazole]. The 50% inhibitory concentration range for 1263W94 was 0.15 to 1. 1 microM, compared with 10 microM for ACV. Thus, 1263W94 is a potent inhibitor of EBV. In addition, 1263W94 inhibited the phosphorylation and the accumulation of the essential EBV replicative cofactor, early antigen D.