The immediate early proteins of varicella-zoster virus

Everolimus delayed and suppressed cytomegalovirus DNA synthesis, spread of the infection, and alleviated cytomegalovirus infection

Everolimus is an inhibitor of mammalian target of rapamycin (mTOR) and reduces the risk of cytomegalovirus (CMV) infection in transplant recipients. Everolimus inhibits mTOR complex 1, which regulates factors involved in several crucial cellular functions and is required for CMV replication. However, it is not clear how everolimus regulates CMV replication and prevents and alleviates CMV infection. Effects of everolimus on CMV infection, spread, and DNA synthesis and release from infected cells were assessed by plaque formation, infectious centre assay, real-time PCR of infected cells, and culture supernatant in CMV-infected cultures with and without everolimus. Everolimus enhanced plaque formation by 3.6 times, but the size of the plaques was reduced to 36.4% of untreated cultures in the absence of a pretreatment period. Everolimus reduced viral adsorption but enhanced the replication efficiency of inoculated virus, resulting in an increase in plaque number in the early phase of infection. Preinfection treatment of cells with everolimus efficiently exhibited its antiviral efficacy, and everolimus delayed and suppressed viral DNA synthesis and release from infected cells. Everolimus had suppressed the spread of infection and reduced the number of total infected cells to 40% of untreated cells on day 9, indicating reduction of the size of CMV lesions to one-sixth in 2-3 replication cycles. Preinfection treatment of the cells with everolimus augmented its suppressive effect on CMV infection and replication. Everolimus reduced the total number of infected cells and limited the CMV lesions, and this reduction in the spread of CMV infection would alleviate CMV infection in transplant recipients.

Antibody to varicella-zoster virus immediate-early protein 62 augments allodynia in zoster via brain-derived neurotrophic factor

Varicella-zoster virus (VZV) expresses immediate-early protein 62 (IE62), and zoster is associated with neuropathic pain. Brain-derived neurotrophic factor (BDNF) is involved in the neuronal mechanism underlying pain hypersensitivity. Zoster is associated with prodrome and the robust production of booster antibody to VZV. We hypothesized that the intrathecal production of antibody to IE62 cross-reacting with BDNF and the nerve injury by skin lesions may augment allodynia in zoster by enhancing BDNF activity. One of three monoclonal antibodies against the 268-556 peptide of IE62 recognized BDNF. Immunological cross-reactivity between IE62 and BDNF and the effects of anti-IE62 monoclonal antibody (anti-IE62 MAb) cross-reactivity with BDNF on BDNF activity in cultured neurons were examined. Anti-IE62 MAb and anti-BDNF MAbs recognized the 414-429 peptide of IE62 and the BDNF dimer. Anti-IE62 MAb significantly augmented BDNF-related transcription in neurons and the morphological development of spinal dorsal horn neurons. Sera from patients recognized IE62 and BDNF and enhanced BDNF activity in neurons. The effect of anti-IE62 antibody on mechanical allodynia was characterized by the threshold of allodynia using von Frey filaments in a spinal nerve injury (SNI) in mice. The administration of anti-IE62 MAb to or immunization with cross-reacting IE62 protein to mice significantly enhanced mechanical allodynia on the side with SNI but not on the uninjured side. Anti-IE62 antibody augmented BDNF activity in neurons and allodynia in mice with SNI. The intrathecal production of anti-IE62 antibody augmenting BDNF activity and peripheral nerve injury by zoster may participate in the pathogenesis of allodynia in zoster.

Isolation of therapeutic human monoclonal antibodies for varicella-zoster virus and the effect of light chains on the neutralizing activity

Therapeutic antibodies against varicella-zoster virus (VZV) were isolated from a combinatorial library of human antibodies using a phage-display system. Purified gH:gL was used to screen the library, and approximately 300 clones were isolated. Eight kinds of Fab-cp3-fused molecules (clones 10, 24, 36, 60, 94, 120, 192, and 431) neutralized viral infectivity. After conversion of Fab-cp3 antibodies to the Fab-protein A form, the concentrations of antibodies showing 50% inhibition of plaque formation ranged from 0.12 to 400 nM. Clones 10, 24, 94, 120 and 431 neutralized wild strains without showing strain specificity and were further converted to human IgG(1). Two clones (24 and 94) were confirmed to react with gH:gL and VZV-infected cells. IgG of clone 94 prevented spreading of infected cells. Thus these antibodies exhibited the typical phenotype of anti-gH antibody. Next the contribution of light (L) chains to neutralizing activity was analyzed by comparing the effect of L chain of clones 10, 120, and 192 with the identical heavy chain on their neutralizing activity. The L chain in the Fab form of clone 94 was replaced by L chains of clones 10, 24, 36, and 60 and the neutralizing activity of these replaced antibodies was weaker than that of the prototype clone 94. When the kappa-L chain of clone 94 was replaced by the lambda-L chain of clone 24, this antibody possessed neutralizing activity despite the kappa-lambda class change. Thus, human antibody library against VZV-gH has been established and characterized the role of the L chain in VZV-neutralizing activity to engineering further an antibody with stronger neutralizing activity.

Posttranslational modification and cell type-specific degradation of varicella-zoster virus ORF29p

The ORF29 gene of varicella-zoster virus encodes a single-stranded DNA binding protein that is predominantly nuclear during lytic infection but appears to be restricted to the cytoplasm of latently infected neurons. Following reactivation, ORF29p accumulates in the nuclei of neurons, suggesting that its confinement to the cytosol may be critical for maintaining quiescence. When autonomously expressed, ORF29p accumulates in the nuclei of fibroblasts and the cytoplasm of cells (guinea pig enteric neurons) and cell lines (U373MG) of neuronal origin. Inhibition of the 26S proteasome redirects the accumulation of ORF29p to the nucleus in cells of neuronal origin. Here, we show that ORF29p is ubiquitinated and sumoylated in 293T cells and subsequently degraded from the N terminus. Ubiquitinated ORF29p accumulates in both the nuclei and the cytoplasm of fibroblasts, but degradation products are seen primarily in the cytoplasm. Modification and degradation of ORF29p occurs in 293T, U373MG, and MeWo cells. Therefore, these processes are ubiquitous; however, the robustness of the degradation process is cell type specific. The proteasome-mediated mechanism of nuclear exclusion in U373MG cells is an active process that is not specific for the endogenous ORF29p nuclear localization signal but can be saturated by protein stabilization or overexpression, which leads to nuclear accumulation of ORF29p. The evidence for ORF29p ubiquitination and previous data regarding the effect of proteasome inhibitors on the abundance and distribution of ORF29p implicate the 26S proteasome in influencing the protein's cell type-specific localization.

Downregulation of varicella-zoster virus (VZV) immediate-early ORF62 transcription by VZV ORF63 correlates with virus replication in vitro and with latency

Varicella-zoster virus (VZV) open reading frame 63 (ORF63) protein is expressed during latency in human sensory ganglia. Deletion of ORF63 impairs virus replication in cell culture and establishment of latency in cotton rats. We found that cells infected with a VZV ORF63 deletion mutant yielded low titers of cell-free virus and produced very few enveloped virions detectable by electron microscopy compared with those infected with parental virus. Microarray analysis of cells infected with a recombinant adenovirus expressing ORF63 showed that transcription of few human genes was affected by ORF63; a heat shock 70-kDa protein gene was downregulated, and several histone genes were upregulated. In experiments using VZV transcription arrays, deletion of ORF63 from VZV resulted in a fourfold increase in expression of ORF62, the major viral transcriptional activator. A threefold increase in ORF62 protein was observed in cells infected with the ORF63 deletion mutant compared with those infected with parental virus. Cells infected with ORF63 mutants impaired for replication and latency (J. I. Cohen, T. Krogmann, S. Bontems, C. Sadzot-Delvaux, and L. Pesnicak, J. Virol. 79:5069-5077, 2005) showed an increase in ORF62 transcription compared with those infected with parental virus. In contrast, cells infected with an ORF63 mutant that is not impaired for replication or latency showed ORF62 RNA levels equivalent to those in cells infected with parental virus. The ability of ORF63 to downregulate ORF62 transcription may play an important role in virus replication and latency.

Comparative efficacy of acyclovir and vidarabine on the replication of varicella-zoster virus

Acyclovir and less frequently, vidarabine are (or have been) used in the treatment of varicella-zoster virus (VZV) infection and are administered either intravenously (vidarabine) or orally (acyclovir, up to five times per day). The pharmacological bases of the administration interval were modeled in vitro in this study. Incubation of VZV-infected cultures with acyclovir or vidarabine for 24, 48, 72 and 96h showed similar duration-dependent anti-viral activities as assessed by a plaque-reduction assay. Treatment with vidarabine for only 8h/day for 4 days (intermittent treatment) showed anti-VZV activity equivalent to that of continuous treatment for 4 days in terms of the inhibitory dose that reduced plaque formation by 50% (IC(50)). In contrast, intermittent treatment with acyclovir exhibited a 7.9 times higher IC(50) value than that of continuous treatment. The mode of inhibition of expression of most of viral protein was similar in both drugs, but the degree of inhibition was different for each protein. Thus, vidarabine with a limited period of treatment showed anti-VZV activity comparable to continuous treatment with acyclovir, indicating the longer duration of anti-viral activity of vidarabine.

Clinical and molecular pathogenesis of varicella virus infection

Varicella zoster virus (VZV) is a neurotropic human herpesvirus that infects nearly all humans and causes chickenpox (varicella). After chickenpox, VZV becomes latent in cranial nerve, dorsal root, and autonomic nervous system ganglia along the entire neuraxis. Virus reactivation produces shingles (zoster), characterized by pain and rash usually restricted to 1-3 dermatomes. Zoster is often complicated by postherpetic neuralgia (PHN), pain that persists for months to years after rash resolves. Virus may also spread to the spinal cord and blood vessels of the brain, producing a unifocal or multifocal vasculopathy, particularly in immunocompromised individuals. The increased incidence of zoster in elderly and immunocompromised individuals appears to be due to a VZV-specific host immunodeficiency. PHN may reflect a chronic VZV ganglionitis, and VZV vasculopathy is due to productive virus infection in cerebral arteries. Strategies that might boost host cell-mediated immunity to VZV are discussed, as well as the physical state of viral nucleic acid during latency and the possible mechanisms by which herpesvirus latency is maintained and virus is reactivated. A current summary of varicella latency and pathogenesis produced by simian varicella virus (SVV), the counterpart of human VZV, points to the usefulness of a primate model of natural infection to study varicella latency, as well as the experimental model of intratracheal inoculation to study the effectiveness of antiviral agents in driving persistent varicella virus into a latent state.

Varicella-zoster virus gene 66 transcription and translation in latently infected human Ganglia

Latent infection with varicella-zoster virus (VZV) is characterized by restricted virus gene expression and the absence of virus production. Of the approximately 70 predicted VZV genes, only five (genes 4, 21, 29, 62, and 63) have been shown by multiple techniques to be transcribed during latency. IE62, the protein product of VZV gene 62, is the major immediate-early (IE) virus-encoded transactivator of viral gene transcription and plays a pivotal role in transactivating viral genes during lytic infection. The protein kinase (66-pk) encoded by VZV gene 66 phosphorylates IE62, resulting in cytoplasmic accumulation of IE62 that mitigates nuclear IE62-induced gene activation. Analysis of latently infected human trigeminal ganglia for 66-pk expression by reverse transcriptase-dependent nested PCR, including DNA sequence analysis, in situ hybridization, and immunohistochemistry, revealed VZV open reading frame 66 to be a previously unrecognized latently expressed virus gene and suggests that prevention of IE62 import to the nucleus by VZV 66-pk phosphorylation is one possible mechanism by which VZV latency is maintained.

Varicella-zoster virus open reading frame 21, which is expressed during latency, is essential for virus replication but dispensable for establishment of latency

Varicella-zoster virus (VZV) open reading frame 21 (ORF21) is one of at least five VZV genes expressed in latently infected human and rodent ganglia. To determine whether ORF21 is required for latent and lytic infection, we deleted 99% of ORF21 from the viral genome. The ORF21 deletion mutant virus could be propagated only in a cell line expressing the ORF21 protein. Insertion of the herpes simplex virus type 1 (HSV-1) homolog of VZV ORF21, HSV-1 UL37, into the ORF21 deletion mutant failed to complement the mutant for growth in cell culture. Inoculation of cotton rats with the ORF21 deletion virus resulted in latent infection in numbers of animals similar to those infected after inoculation with the parental virus. The mean numbers of latent VZV genomes were similar in animals infected with parental and ORF21 deletion viruses. Transcription of ORF63, another latency-associated gene, was detected in ganglia from similar numbers of animals infected with the mutant and parental viruses. Thus, ORF21 is the first VZV gene expressed during latency that has been shown to be dispensable for the establishment of latent infection.

Physical and functional interaction between the varicella zoster virus IE63 and IE62 proteins

The varicella zoster virus (VZV) IE63 protein is required for growth of the virus in cell culture and is expressed during both lytic and latent phases of VZV infection. We have investigated the physical and functional interaction of this protein with the major VZV transactivating protein IE62. The region of the IE63 protein required for interaction with the IE62 protein has been identified and encompasses the N-terminal 142 amino acids. We have found that the interaction is stable at physiological ionic strength. We have also shown that a portion of the IE63 and IE62 proteins colocalize in VZV-infected cells at both 15 and 48 h postinfection. IE63 was found to have no transcriptional activating or repressing activity within the context of a minimal VZV glycoprotein promoter. The presence of the IE63, however, upmodulated the IE62 transactivation of this promoter. Finally, we show that the IE63 protein can be coimmunoprecipitated with the cellular RNA polymerase II from infected cell extracts, indicating that it is present in a complex with that enzyme.

Construction of Oka varicella vaccine expressing human immunodeficiency virus env antigen

Oka varicella vaccine has been used to confer active immunity to varicella-zoster virus (VZV) in healthy and immunocompromised hosts. Based on its attenuated nature, Oka varicella vaccine expressing human immunodeficiency virus (HIV) env antigen was constructed by inserting the HIVenv gene into the viral genome and its immunogenicity was assessed in guinea pigs. The HIVenv gene encoding 296-463 amino acids was inserted between the sequences of the hepatitis B surface antigen and the thymidine kinase gene of the cloned plasmid and the recombinant virus was isolated by cotransfection of the chimeric plasmid with viral DNA. Insertion of the HIVenv gene into the viral genome was confirmed by PCR and sequencing of the viral genome of the recombinant virus. The recombinant virus expressed 30k HIVenv fusion protein in its infected cells. In guinea pigs, immunization with the recombinant virus induced an antibody response to both the HIV antigen and the V3 peptide of gp120 as well as VZV gE:gI. Cell-mediated immunity to the HIV antigen and gE:gI was assessed by the cutaneous reaction representing delayed type hypersensitivity. Immunized guinea pigs responded well to both the HIV antigen and gE:gI. Thus the recombinant Oka varicella vaccine expressing the HIVenv antigen induced both a humoral and cell-mediated immunity to the HIV antigen similar to VZV as Oka varicella vaccine induces humoral and cell-mediated immunity to VZV in the vaccinees. This recombinant Oka varicella vaccine expressing the HIVenv antigen may be evaluated for its immunogenicity as one of the AIDS vaccine candidates.

The role of varicella zoster virus immediate-early proteins in latency and their potential use as components of vaccines

Varicella zoster virus immediate-early (IE) proteins are intracellular regulators of viral gene expression. Some of them (IE62 and IE63) are found in large amounts in infected cells but are also components of the virion tegument. Several IE and early genes are transcribed during latency, while late genes are not. Recently, we demonstrated the presence of protein IE 63 in dorsal root ganglia of persistently infected rats as well as in normal human ganglia; other IE proteins have been found since in human ganglia. Cell-mediated immunity (CMI) to IE 62 has been evidenced. We found both humoral immunity and CMI to IE 63 in immune adults. In elderly zoster-free individuals, CMI to IE 63 remained high. The differences in the CMI to IE 63 among young adults, elderly people and immunocompromized patients have to be analyzed according to their status relative to zoster, to determine whether the decrease in CMI, particularly to IE proteins, could be responsible for viral reactivation and for the onset of shingles. Hopefully, the waning of the CMI to VZV IE 63 and perhaps to other IE proteins could become a predictive marker for herpes zoster and reimmunization, not only with the vaccine strain, but also with purified IE proteins could help prevent zoster at old age.

Varicella-zoster virus gE escape mutant VZV-MSP exhibits an accelerated cell-to-cell spread phenotype in both infected cell cultures and SCID-hu mice

Varicella-zoster virus is considered to have one of the most stable genomes of all human herpesviruses. In 1998, we reported the unanticipated discovery of a wild-type virus that had lost an immunodominant B-cell epitope on the gE ectodomain (VZV-MSP); the gE escape mutant virus exhibited an unusual pattern of egress. Further studies have now documented a markedly enhanced cell-to-cell spread by the mutant virus in cell culture. This property was investigated by laser scanning confocal microscopy combined with a software program that allows the measurement of pixel intensity of the fluorescent signal. For this new application of imaging technology, the VZV immediate early protein 62 (IE 62) was selected as the fluoresceinated marker. By 48 h postinfection, the number of IE 62-positive pixels in the VZV-MSP-infected culture was nearly fourfold greater than the number of pixels in a culture infected with a low-passage laboratory strain. Titrations by infectious center assays supported the above image analysis data. Confirmatory studies in the SCID-hu mouse documented that VZV-MSP spread more rapidly than other VZV strains in human fetal skin implants. Generally, the cytopathology and vesicle formation produced by other strains at 21 days postinfection were demonstrable with VZV-MSP at 14 days. To assess whether additional genes were contributing to the unusual VZV-MSP phenotype, approximately 20 kb of the VZV-MSP genome was sequenced, including ORFs 31 (gB), 37 (gH), 47, 60 (gL), 61, 62 (IE 62), 66, 67 (gI), and 68 (gE). Except for a few polymorphisms, as well as the previously discovered mutation within gE, the nucleotide sequences within most open reading frames were identical to the prototype VZV-Dumas strain. In short, VZV-MSP represents a novel variant virus with a distinguishable phenotype demonstrable in both infected cell cultures and SCID-hu mice.

Varicella-zoster virus ORF61 deletion mutants replicate in cell culture, but a mutant with stop codons in ORF61 reverts to wild-type virus

Varicella-zoster virus (VZV) ORF61 encodes a phosphoprotein that transactivates VZV promoters. Transfection of cells with cosmid DNAs, including a cosmid with a large deletion in ORF61, resulted in a VZV ORF61 deletion mutant that was impaired for growth in vitro and could be partially complemented by growth in neuroblastoma or osteosarcoma cell lines. Cells infected with the VZV ORF61 deletion mutant expressed normal levels of an immediate-early VZV protein, but had reduced levels of a late protein and showed abnormal syncytia. Carboxy terminal truncation mutants of VZV ORF61 protein have a transrepressing phenotype and inhibit the infectivity of cotransfected wild-type viral DNA. Transfection of cells with cosmid DNAs, including a cosmid with stop codons that should result in an ORF61 truncation mutant expressing a transrepressing protein that retains the RING finger domain, resulted in a viral genome which reverted back to the wild-type sequence. BAL-31 exonuclease was used to produce deletions at the site of the stop codons in ORF61 of the cosmid, resulting in loss of the RING finger domain. Transfection of tissue culture cells with the ORF61 BAL-31 deletion mutants and other cosmid DNAs yielded viable viruses. Thus, while deletion mutants lacking the RING finger domain of ORF61 replicate in cell culture, a mutant with stop codons that retains this domain could not be propagated and reverted to wild-type virus.

Varicella-zoster virus glycoprotein I is essential for growth of virus in Vero cells

Varicella-zoster virus (VZV) encodes at least six glycoproteins. Glycoprotein I (gI), the product of open reading frame 67, is a 58- to 62-kDa glycoprotein found in VZV-infected cells. We constructed two VZV gI deletion mutants. Immunoprecipitation of VZV gE from infected cells indicated that cells infected with VZV deleted for gI expressed a gE that was larger (100 kDa) than that expressed in cells infected with the parental virus (98 kDa). Cell-associated or cell-free VZV deleted for gI grew to lower titers in melanoma cells than did parental VZV. While VZV deleted for gI replicated in other human cells, the mutant virus replicated to very low titers in primary guinea pig and monkey cells and did not replicate in Vero cells. When compared with the parental virus, rescued viruses, in which the gI deletion was restored with a wild-type allele, showed a similarly sized gE and comparable growth patterns in melanoma and Vero cells. VZV deleted for gI entered Vero cells; however, viral DNA synthesis was impaired in these cells. The VZV gI mutant was slightly impaired for adsorption to human cells. Thus, VZV gI is required for replication of the virus in Vero cells, for efficient replication of the virus in nonhuman cells, and for normal processing of gE.

Lessons to be learned from varicella-zoster virus

Varicella-zoster virus (VZV) is an alphaherpesvirus responsible for two human diseases: chicken pox and shingles. The virus has a respiratory port of entry. After two successive viremias, it reaches the skin where it causes typical lesions. There, it penetrates the peripheral nervous system and it remains latent in dorsal root ganglia. It is still debatable whether VZV persists in neurons or in satellite cells. During latency, VZV expresses a limited set of transcripts of its immediate early (IE) and early (E) genes but no protein has been detected. Mechanisms of reactivation from ganglia have not been identified. However, dysfunction of the cellular immune system appears to be involved in this process. The cell-associated nature of VZV has made it difficult to identify a temporal order of gene expression, but there appears to be a cascade mechanism as for HSV-1. The lack of high titre cell-free virions or recombination mutants has hindered so far the understanding of VZV gene functions. Five genes, ORFs 4, 10, 61, 62, and 63 that encode regulatory proteins could be involved in VZV latency. ORF4p activates gene promoters with basal activities. ORF10p seems to activate the ORF 62 promoter. ORF61p has trans-activating and trans-repressing activities. The major IE protein ORF62p, a virion component, has DNA-binding and regulatory functions, transactivates many VZV promoters and even regulates its own expression. ORF63p is a nuclear IE protein of yet unclear regulatory functions, abundantly expressed very early in infection. We have established an animal model of VZV latency in the rat nervous system, enabling us to study the expression of viral mRNA and protein expression during latency, and yielding results similar to those found in humans. This model is beginning to shed light on the molecular events in VZV persistent infection and on the regulatory mechanisms that maintain the virus in a latent stage in nerve cells.

Varicella-zoster virus. The virus

Varicella-zoster virus (VZV) causes chickenpox and herpes zoster. After acute infection the virus becomes latent in dorsal root and trigeminal ganglia for the lifetime of the individual. The viral genome encodes about 70 proteins, at least three of which are thought to be expressed during latency in humans. VZV grows in cell culture, but is very cell-associated; it is relatively difficult to obtain high titers of cell-free virus.

The transcriptional regulatory proteins encoded by varicella-zoster virus open reading frames (ORFs) 4 and 63, but not ORF 61, are associated with purified virus particles

Of the five varicella-zoster virus (VZV) open reading frames (ORFs) known to encode proteins which influence viral transcriptional events, two (ORFs 10 and 62) encode proteins associated with the tegument of virus particles, where they may function during the immediate-early events of infection. In this study, antibodies which recognize the products of the three additional VZV ORFs, ORFs 4, 61, and 63, were made and used to characterize their association with virus particles. ORF 4 encoded a 52-kDa polypeptide, and antibodies to ORF 63 reacted with polypeptides of 47 and 28 kDa. Antibodies to ORF 61 recognized heterogeneous polypeptides of 62 to 66 kDa in cells infected with a vaccinia virus recombinant expressing ORF 61 and in VZV-infected melanoma cells but reacted very weakly with polypeptides of VZV-infected human foreskin fibroblasts, suggesting that cell-specific factors were involved in ORF 61 protein accumulation. Analysis of virus particles purified from melanoma cells indicated that a 52-kDa polypeptide from ORF 4 and the 47-kDa polypeptide from ORF 63, but not any from ORF 61, were associated with virus particles. The virion proteins were likely components of the tegument, as they were not solubilized by treatment of virus with mild detergents and were completely resistant to trypsin digestion unless prior envelope solubilization was performed. The products of ORFs 4 and 63 were not found in purified VZV nucleocapsids. These results suggest that forms of the ORF 4- and ORF 63-encoded transcriptional regulatory proteins are also structural and may also have roles in the immediate-early events of infection.

Varicella-zoster virus gene 63 encodes an immediate-early protein that is abundantly expressed during latency

Varicella-zoster virus (VZV) gene 63 encodes a protein with a predicted molecular mass of 30.5 kDa which has amino acid similarities with the immediate-early (IE) protein 22 (ICP-22) of herpes simplex virus type 1. In order to study the expression of this protein during lytic and latent infection, gene 63 was cloned in frame and downstream from the glutathione-S-transferase gene, expressed as a fusion protein, and purified. In VZV-infected Vero cells, antibodies directed against this protein detect two polypeptides of 45 and 38 kDa which are localized both in the cytoplasm and in the nucleus. Using a sequential combination of transcription and protein synthesis inhibitors (actinomycin D and cycloheximide, respectively), we demonstrated the immediate-early nature of this protein, which can thus be named IE63. Using a rat model of VZV latency, we showed that IE63 is heavily expressed, essentially in neurons, during latency. IE63 can also be detected in the skin of patients showing early herpes zoster symptoms.

Mutational analysis of varicella-zoster virus major immediate-early protein IE62

The varicella-zoster virus (VZV) open reading frame 62 encodes an immediate-early protein (IE62) that transactivates expression of various VZV promoters and autoregulates its own expression in transient expression assays. In Vero cells, IE62 was shown to transactivate the expression of all putative immediate-early (IE) and early (E) genes of VZV with an up-regulating effect at low intracellular concentrations. To define the functional domains involved in the regulatory properties of IE62, a large number of in-frame insertions and deletions were introduced into a plasmid-borne copy of the gene encoding IE62. Studies of the regulatory activities of the resultant mutant polypeptides in transient expression assays allowed to delineate protein regions important for repression of its own promoter and for transactivation of a VZV putative immediate-early gene (ORF61) promoter and an early gene (ORF29) promoter. This mutational analysis resulted in the identification of a new functional domain situated at the border between regions 4 and 5 which plays a crucial role in the IE62 regulatory functions. This domain turned out to be very well conserved amongst homologous alphaherpesvirus regulatory proteins and appeared to be rich in bulky hydrophobic and proline residues, similar to the proline-rich region of the CAAT box binding protein CTF-1. By immunofluorescence, a nuclear localization signal has been mapped in region 3.

Nucleotide sequence of infectious laryngotracheitis virus (gallid herpesvirus 1) ICP4 gene

The infectious laryngotracheitis virus (ILTV) gene encoding a homologue to the ICP4 protein of herpes simplex virus (HSV) has been mapped to the inverted repeat region. The complete nucleotide sequence of ILTV ICP4 has been determined. The ILTV ORF encoding ICP4 is 4386 nucleotides long, calculated from the first of four ATG codons, and has an overall G+C content of 59%. The ILTV ICP4 contains two domains of high homology which have been reported in other studies to be conserved in the ICP4 homologues of alphaherpesviruses, and to be functionally important. Several regulatory features were identified including a serine-rich domain in region one. A more extensive serine-rich domain was located in region five which is also found in varicella-zoster virus (VZV) and bovine herpesvirus 1. A 5.4 kb immediate early transcript was identified in infected primary kidney cells.

Varicella-zoster virus (VZV) open reading frame 10 protein, the homolog of the essential herpes simplex virus protein VP16, is dispensable for VZV replication in vitro

Varicella-zoster virus (VZV) open reading frame 10 (ORF10) protein in the homolog of the herpes simplex virus type 1 (HSV-1) protein VP16. VZV ORF10 transactivates the VZV IE62 gene and is a tegument protein present in the virion. HSV-1 VP16, a potent transactivator of HSV-1 immediate-early genes and tegument protein, is essential for HSV-1 replication in vitro. To determine whether VZV ORF10 is required for viral replication in vitro, we constructed two VZV mutants which were unable to express ORF10. One mutant had a stop codon after the 61st codon of the ORF10 gene, and the other mutant was deleted for all but the last five codons of the gene. Both VZV mutants grew in cell culture to titers similar to that of the parental virus. To determine whether HSV-1 VP16 alters the growth of VZV, we constructed a VZV mutant in which VP16 was inserted in place of ORF10. Using immune electron microscopy, we found that HSV-1 VP16 was present in the tegument of the recombinant VZV virions. The VZV VP16 substitution mutant produced smaller plaques and grew to a lower titer than parental virus. Thus, VZV ORF10 is not required for growth of the virus in vitro, and substitution of HSV-1 VP16 for VZV ORF10 impairs the growth of VZV.

The cellular transcription factor USF cooperates with varicella-zoster virus immediate-early protein 62 to symmetrically activate a bidirectional viral promoter

The mechanisms governing the function of cellular USF and herpesvirus immediate-early transcription factors are subjects of considerable interest. In this regard, we identified a novel form of coordinate gene regulation involving a cooperative interplay between cellular USF and the varicella-zoster virus immediate-early protein 62 (IE 62). A single USF-binding site defines the potential level of IE 62-dependent activation of a bidirectional viral early promoter of the DNA polymerase and major DNA-binding protein genes. We also report a dominant negative USF-2 mutant lacking the DNA-binding domain that permits the delineation of the biological role of both USF-1 and USF-2 in this activation process. The symmetrical stimulation of the bidirectional viral promoter by IE 62 is achieved at concentrations of USF-1 (43 kDa) or USF-2 (44 kDa) already existing in cells. Our observations support the notion that cellular USF can intervene in and possibly target promoters for activation by a herpesvirus immediate-early protein.

The cellular transcription factor USF cooperates with varicella-zoster virus immediate-early protein 62 to symmetrically activate a bidirectional viral promoter

The mechanisms governing the function of cellular USF and herpesvirus immediate-early transcription factors are subjects of considerable interest. In this regard, we identified a novel form of coordinate gene regulation involving a cooperative interplay between cellular USF and the varicella-zoster virus immediate-early protein 62 (IE 62). A single USF-binding site defines the potential level of IE 62-dependent activation of a bidirectional viral early promoter of the DNA polymerase and major DNA-binding protein genes. We also report a dominant negative USF-2 mutant lacking the DNA-binding domain that permits the delineation of the biological role of both USF-1 and USF-2 in this activation process. The symmetrical stimulation of the bidirectional viral promoter by IE 62 is achieved at concentrations of USF-1 (43 kDa) or USF-2 (44 kDa) already existing in cells. Our observations support the notion that cellular USF can intervene in and possibly target promoters for activation by a herpesvirus immediate-early protein.

Transcriptional mapping of the varicella-zoster virus regulatory genes encoding open reading frames 4 and 63

Four of the 68 varicella-zoster virus (VZV) unique open reading frames (ORFs), i.e., ORFs 4, 61, 62, and 63, encode proteins that influence viral transcription and are considered to be positional homologs of herpes simplex virus type 1 (HSV-1) immediate-early (IE) proteins. In order to identify the elements that regulate transcription of VZV ORFs 4 and 63, the encoded mRNAs were mapped in detail. For ORF 4, a major 1.8-kb and a minor 3.0-kb polyadenylated [poly(A)+] RNA were identified, whereas ORF 63-specific probes recognized 1.3- and 1.9-kb poly(A)+ RNAs. Probes specific for sequences adjacent to the ORFs and mapping of the RNA 3' ends indicated that the ORF 4 RNAs were 3' coterminal, whereas the RNAs for ORF 63 represented two different termination sites. S1 nuclease mapping and primer extension analyses indicated a single transcription initiation site for ORF 4 at 38 bp upstream of the ORF start codon. For ORF 63, multiple transcriptional start sites at 87 to 95, 151 to 153, and (tentatively) 238 to 243 bp upstream of the ORF start codon were identified. TATA box motifs at good positional locations were found upstream of all mapped transcription initiation sites. However, no sequences resembling the TAATGARAT motif, which confers IE regulation upon HSV-1 IE genes, were found. The finding of the absence of this motif was supported through analyses of the regulatory sequences of ORFs 4 and 63 in transient transfection assays alongside those of ORFs 61 and 62. Sequences representing the promoters for ORFs 4, 61, and 63 were all stimulated by VZV infection but failed to be stimulated by coexpression with the HSV-1 transactivator Vmw65. In contrast, the promoter for ORF 62, which contains TAATGARAT motifs, was activated by VZV infection and coexpression with Vmw65. These results extend the transcriptional knowledge for VZV and suggest that ORFs 4 and 63 contain regulatory signals different from those of the ORF 62 and HSV-1 IE genes.

The DNA binding domains of the varicella-zoster virus gene 62 and herpes simplex virus type 1 ICP4 transactivator proteins heterodimerize and bind to DNA

The product of varicella-zoster virus gene 62 (VZV 140k) is the functional counterpart of the major transcriptional regulatory protein of herpes simplex virus type 1 (HSV-1), ICP4. We have found that the purified bacterially expressed DNA binding domain of VZV 140k (residues 417-647) is a stable dimer in solution. As demonstrated by the appearance of a novel protein--DNA complex of intermediate mobility in gel retardation assays, following in vitro co-translation of a pair of differently sized VZV 140k DNA binding domain peptides, the 140k DNA binding domain peptide binds to DNA as a dimer. In addition, the DNA binding domain peptide of HSV-1 ICP4 readily heterodimerizes with the VZV 140k peptide on co-translation, indicating that HSV-1 ICP4 and VZV 140k possess very similar dimerization interfaces. It appears that only one fully wild type subunit of the dimer is sufficient to mediate sequence specific DNA recognition in certain circumstances. Co-immunoprecipitation analysis of mutant DNA binding domain peptides, co-translated with an epitope-tagged ICP4 DNA binding domain, shows that the sequence requirements for dimerization are lower than those necessary for DNA binding.

A major transactivator of varicella-zoster virus, the immediate-early protein IE62, contains a potent N-terminal activation domain

Accumulating evidence indicates that the product of the putative immediate-early gene ORF62 (IE62) activates varicella-zoster virus (VZV) genes thought to represent all three kinetic classes, namely, immediate-early (alpha), early (beta), and late (gamma) classes, of VZV genes as well as a variety heterologous gene promoters. However, the mechanism(s) by which IE62 protein mediates transactivation of these diverse VZV and heterologous gene promoters remains to be elucidated. In this study, by using yeast GAL4 protein chimeras, the coding regions of VZV ORF62 possessing activation domains have been assessed. We demonstrate that the VZV IE62 protein contains a potent activation domain in the N-terminal portion of the molecule, encoded within the first 86 codons of ORF62. The predicted secondary structure profile and the acid-base composition of this IE62 domain resemble those of other transregulatory proteins whose activation is mediated through acidic, hydrophobic elements. In addition, we show that deletion of this activation domain from the 1,310-residue native IE62 protein results in ablation of the transactivator function of IE62. We also present evidence that the mutant IE62 protein lacking the activation domain, though devoid of transactivation ability, was still capable of interfering with the activation of target promoters by the native, full-length IE62.

Characterization of the regulatory functions of varicella-zoster virus open reading frame 4 gene product

Varicella-zoster virus (VZV) open reading frame 4 (ORF4) encodes a protein with a predicted molecular weight of 51,540 presenting amino acid sequence homology with the immediate-early regulatory protein ICP27 of herpes simplex virus type 1. To investigate the regulatory properties of the ORF4 gene product, we performed a series of transient expression assays in Vero cells, using a plasmid expressing ORF4 as effector and several VZV genes and heterologous genes as targets. The VZV target plasmids contained promoter/regulatory regions from genes belonging to the three putative VZV kinetic classes fused to the chloramphenicol acetyltransferase (CAT) gene. The heterologous target plasmids consisted of promoter/regulatory regions of human cytomegalovirus, Rous sarcoma virus, and human immunodeficiency virus type 1 fused to the reporter gene. These experiments demonstrated that the ORF4 gene product activated expression of ORF62 in a dose-dependent fashion but had no effect on the expression of the three other putative immediate-early genes (ORF4, ORF61, and ORF63). When various amounts of ORF4 were transfected in the presence of early gene promoters, dose-dependent transactivation was evidenced with the thymidine kinase gene (ORF36) and the major DNA-binding protein gene (ORF29) promoters; interestingly, little activity was detected with the promoter of the DNA polymerase gene (ORF28). No activation of late gene expression, represented by the glycoprotein I and glycoprotein II genes, was seen even over a wide range of concentrations of input ORF4 plasmid. Expression of pCMVCAT, pRSVCAT, and pHIVCAT was also stimulated by the ORF4 gene product. CAT mRNA analysis showed that activation of VZV target promoters occurs at the transcriptional and/or posttranscriptional level.

The DNA binding domain of the varicella-zoster virus gene 62 protein interacts with multiple sequences which are similar to the binding site of the related protein of herpes simplex virus type 1

Varicella-zoster virus gene 62 encodes a protein with predicted Mr of 140,000D (VZV 140k) that shares extensive predicted amino acid sequence homology with the major immediate early (IE) transcriptional regulator protein of herpes simplex virus type 1 (HSV-1) Vmw175. The integrity of highly conserved region 2 is essential for the DNA binding and transcriptional regulatory functions of Vmw175. Similarly, an insertion mutation in region 2 (codons 468-641) of 140k eliminates the transcriptional repression and activation functions of this protein. We have expressed a fragment of 140k which encompasses region 2 as a non-fusion polypeptide in bacteria. This 140k DNA binding domain peptide (codons 417-646) binds to numerous DNA sequences throughout the VZV gene 62 promoter region. It induces multiple regions of protection from DNase I digestion, flanked by sites of DNase I hypersensitivity. Several of the sites recognized can be considered to be divergent forms of the consensus sequence which is recognized by Vmw175. However, by use of a panel of mutagenized probe fragments, we found that the 140k DNA binding domain was less sequence-specific than Vmw175 in its interactions with DNA. Consistent with this, the homologous Vmw175 DNA binding domain, and also intact Vmw175, recognize the gene 62 binding sites much less efficiently than the 140k DNA binding domain. Also in contrast to the situation with Vmw175, the 140k DNA binding domain failed to induce DNA bending when occupying the binding sites in its own promoter. Deletion analysis has mapped the minimal DNA binding domain of the VZV 140k protein, as measured in gel retardation analysis, to lie within residues 472 to 633. The differences in binding characteristics of the DNA binding domains of the homologous VZV 140k and HSV-1 Vmw175 IE proteins may account for the subtle differences in their regulatory activities in transfection assays and during virus growth in tissue culture.

The varicella-zoster virus immediate early protein, IE62, can positively regulate its cognate promoter

Varicella-Zoster virus (VZV) is a neurotropic alphaherpes virus closely related to herpes simplex virus (HSV). However, unlike its close relative HSV, VZV lacks a functional alpha-TIF (alpha-gene transinducing factor) that activates the transcription of immediate early genes during the initial events of the virus life cycle. Hence, in the absence of a functional alpha-TIF, the mechanism triggering the expression of immediate early genes in VZV at present remains unclear. Accumulating evidence indicates that the gene product of the putative immediate early gene ORF62 (IE62) plays a pivotal role in activating VZV genes of all three putative kinetic classes, namely immediate early (alpha), early (beta), and late (gamma) classes of VZV genes. In the present study, we show that IE62 can positively autoregulate its cognate promoter using a transient transfection assay, both in lymphocytes and in neural cells. In the same system, we can also demonstrate activation of the VZV IE62 promoter by HSV ICP4. By deletion analysis and oligonucleotide-directed site-specific mutagenesis we have localized specific regions in the IE62 promoter/upstream sequences that mediate inducibility by IE62 and HSV ICP4, and provide evidence that this promoter activation by these two proteins may be through different mechanisms. These data, taken together with the recent demonstration of the presence of IE62 in the VZ virion tegument (Kinchington, P.R., Hoagland, J.K., Arvin, A.M., Ruyechan, W.T., and Hay, J. 1992. J. Virol. 66, 359-366) provides a possible mechanism by which the triggering of VZV gene expression occurs in the absence of a functional alpha-TIF protein.

Regulation of varicella-zoster virus gene expression in human T lymphocytes

Varicella-zoster virus (VZV), a neurotropic alphaherpesvirus, is the etiologic agent of chicken pox and shingles (zoster) in humans. Using an in vitro transient expression assay, we have evaluated the ability of the putative immediate early VZV genes, ORF4, ORF61, and ORF62 (the analogs of the herpes simplex virus alpha 27, alpha 0, and alpha 4 genes, respectively), to modulate the expression of VZV genes of different putative kinetic classes in a human T lymphocyte cell line. These cells are of the type in which VZV can be readily detected in the viremic phase of human infection. We present evidence to indicate that, in this system, the gene product of ORF62 (IE62) is a major regulatory protein in VZV and is capable of activating VZV genes of all putative kinetic classes. In addition, we demonstrate that the gene product of ORF4 and, unlike the apparent situation in Vero cells, the gene product of ORF61 may play an accessory regulatory role in synergizing the activation of VZV genes induced by the gene product of ORF62 in human T lymphocytes.

The varicella-zoster virus immediate-early protein IE62 is a major component of virus particles

Varicella-zoster virus (VZV) open reading frame (ORF) 62 potentially encodes a protein with considerable amino acid homology to the herpes simplex virus (HSV) immediate-early regulatory polypeptide ICP4 (or IE3). To identify and characterize its protein product(s) (IE62), we used a rabbit antiserum prepared against a synthetic peptide corresponding to the C-terminal 13 amino acids of the predicted protein. This antiserum reacted with phosphorylated polypeptides of 175 to 180 kDa that were made in VZV-infected cells and in cells infected with a vaccinia virus recombinant expressing IE62, but not in control-infected cells, confirming its specificity and reactivity to the IE62 protein. The antiserum recognized a 175-kDa polypeptide in purified virions that comigrated with a major structural protein. Comparison of this reactivity with that of an antipeptide antiserum directed against the VZV ORF 10 product (homologous to the HSV major structural protein VP16) indicates similar levels of ORF 62 and ORF 10 polypeptides in VZV virions. In contrast, antipeptide antiserum directed against the VZV ORF 29 product, the homolog of the HSV major DNA-binding protein, failed to recognize any protein in our virion preparations. Treatment of virions with detergents that disrupt the virion envelope did not dissociate IE62 from the nucleocapsid-tegument structure of the virion. Differential sensitivity of VZV virion IE62 to trypsin digestion in the presence or absence of Triton X-100 indicates that IE62 is protected from trypsin degradation by the virus envelope; since it is not a nucleocapsid protein, we conclude that it is part of the tegument. Finally, we show that the virion 175-kDa protein either can autophosphorylate or is a major substrate in vitro for virion-associated protein kinase activity.

Antibody response to the immediate early protein of cytomegalovirus in renal transplant recipients

The antibody response to the immediate early protein (IEP) of cytomegalovirus (CMV) was examined in seven renal transplant recipients during CMV reactivation and associated clinical abnormalities. Three cases with antibody increase to the IEP in the week after CMV isolation had no CMV-induced disease. The four patients without antibody increase exhibited laboratory abnormalities and three of them had renal dysfunction. In this small number of patients, the antibody response to the IEP in the week after isolation of CMV was associated with absence of abnormal clinical laboratory findings including renal function, and the prognosis was good for graft function in renal transplant recipients with CMV reactivation.

Identification of two protein binding sites within the varicella-zoster virus major immediate early gene promoter

Binding sites for cellular proteins in the promoter of the varicella-zoster virus (VZV) major immediate early (IE) gene were investigated. Protein binding was detected at sequence motifs possessing homology to the CCAAT element and an ATF/AP-1-like binding site, and recognition of the ATF/AP-1 site was apparently facilitated by occupation of the CCAAT site. Gene expression directed by the VZV major IE promoter was stimulated by the adenovirus 5, 289 amino acid EIA gene product. The implications of the results for VZV gene expression and replication are discussed.

The conserved DNA-binding domains encoded by the herpes simplex virus type 1 ICP4, pseudorabies virus IE180, and varicella-zoster virus ORF62 genes recognize similar sites in the corresponding promoters

Herpes simplex virus types 1 and 2 (HSV-1 and HSV-2), pseudorabies virus (PRV), varicella-zoster virus (VZV), and equine herpesvirus 1 (EHV-1) are all classified as Alphaherpesvirinae. Each of these five viruses encodes an essential immediate-early (IE) regulatory protein referred to as HSV-1 ICP4, HSV-2 ICP4, PRV IE180, VZV ORF62 protein, and EHV-1 IE1, respectively. These five proteins share extensive homology with each other in domains referred to as regions 2 and 4. The HSV-1 ICP4 region 2 domain contains residues that are required for the DNA-binding capability of ICP4. In this report, we describe the expression of region 2 domains from the ICP4, IE180, and ORF62 genes as fusion proteins in Escherichia coli. DNA-binding assays revealed that each of these region 2 fusion proteins binds to a sequence that overlaps the transcription start site in the promoter for the gene encoding the corresponding protein. Each of the sites with high affinity for one or more of these fusion proteins contains the sequence 5'-ATCGT-3'. This sequence spans the mRNA cap site in the HSV-2 ICP4 gene promoter and is immediately upstream from the transcription start site in the EHV-1 IE1 gene. These results suggest that formation of a specific complex between an IE protein and its own gene promoter may be a common mechanism used by Alphaherpesvirinae to autoregulate transcription of an essential IE gene.

Acyclovir treatment for varicella does not lower gpI and IE-62 (p170) antibody responses to varicella-zoster virus in normal children

The varicella-zoster virus (VZV) membrane glycoprotein gpI elicits a major immunoglobulin G antibody response after naturally acquired VZV infection; antibody to a nonglycosylated immediate-early protein, IE-62 (p170), represents a response to a nonmembrane VZV component. We evaluated antibody response to VZV gpI and IE-62 (p170) at 28 days and 1 year following infection in 34 children (ages 5 to 16 years) enrolled in a randomized placebo-controlled study of oral acyclovir for the treatment of varicella. All children were VZV antibody negative at enrollment, were previously healthy, and had laboratory-documented varicella. Compared with placebo recipients, acyclovir recipients had lower geometric mean titers by the fluorescent antibody to membrane antigen technique at 28 days (620 versus 836) but similar titers at 1 year (122 versus 122). All children had antibodies to gpI and IE-62 detectable by enzyme-linked immunosorbent assay at 28 days and 1 year. No difference in gpI at 28 days compared with 1 year was noted in acyclovir recipients. No difference in antibody to IE-62 (p170) was noted when acyclovir and placebo recipients were compared at either 28 days or 1 year. Antibody responses to gpI and IE were similar when children were stratified by age (5 to 6 years, 7 to 11 years, 12 to 16 years). A short course of oral acyclovir for the treatment of varicella did not affect antibody responses to gpI or IE-62 (p170) in healthy children at 28 days and 1 year following varicella.

Monoclonal antibody to immediate early protein encoded by varicella-zoster virus gene 62

Monoclonal antibodies (mAbs) were prepared against varicella-zoster virus (VZV)-infected cell proteins, and 10 mAbs which reacted with nuclear antigens were selected. These mAbs recognized a major 175-180 kDa and three minor VZV-specific phosphoprotein species. Immunofluorescence staining of VZV-infected cells showed that the 175-180 kDa protein was synthesized within 6 h after infection. The synthesis of this protein was inhibited by cycloheximide (CH); however, reversal of CH treatment and addition of actinomycin D (ActD) resulted in the synthesis of the 175-180 kDa protein. To determine whether the 175-180 kDa protein seen in the infected cells is encoded by VZV immediate early (IE) gene 62, the predicted open reading frames of VZV genes 61 and 62 were cloned into pGEM transcription vectors. RNA was transcribed from each gene, translated in vitro and immunoprecipitated with a mAb which recognizes a major 175-180 kDa and three minor proteins. The reactivity of the in vitro translation products encoded by gene 62 with this mAb suggested that the 175-180 kDa protein is encoded by VZV IE gene 62.

Trans-activation of viral tk promoters by proteins encoded by varicella zoster virus open reading frames 61 and 62

Plasmids containing the varicella zoster virus (VZV) open reading frames (ORFs) 61 and 62 were used in a transient co-transfection assay to test for trans-activation of the VZV and herpes simplex virus type 1 (HSV-1) thymidine kinase (tk) promoters. The trans-activating potential of the polypeptides encoded by these VZV ORFs, designated p51 and p140, was compared to that of their HSV-1 homologs ICP0 and ICP4, respectively. VZV p51 was functionally inactive in this system while p140 appeared to be a much stronger transcriptional activator than ICP4. Co-transfection of plasmids encoding VZV p140 and HSV-1 ICP0 resulted in a synergistic activation of the reporter gene as has been shown for the combination of ICP4 and ICP0.

Protein analysis of herpes simplex virus latency in vitro established with cycloheximide

Herpes simplex virus (HSV)-specific protein synthesis was examined during establishment of HSV latency and reactivation of virus in human embryonic lung cells treated with cycloheximide and incubated at 40.5 degrees. Eight viral proteins, identified during the first two days of establishment of latency at 40.5 degrees, were undetectable by Day 3. At least two synthesized proteins were present during the maintenance phase of latency. Reactivation of HSV (viral protein 135K) was first detected in latently infected cultures between 2 and 3 hr after superinfection with human cytomegalovirus (HCMV). During this period an 82K protein with the same molecular weight as one of the HCMV immediate-early proteins (82 and 75K) was detected in the immunoprecipitates of latently infected cultures with anti-HSV serum. Thus, this HSV latency system can be used to analyze protein synthesis and clarify reactivation of HSV by HCMV superinfection.

DNA sequence and comparative analyses of the equine herpesvirus type 1 immediate early gene

The immediate early (IE) proteins of herpesviruses are important regulatory factors which control the expression of genes at the transcriptional level. We report the DNA sequence of the immediate early gene of the alphaherpesvirus equine herpesvirus type 1 (EHV-1). This sequence is shown to be extremely rich in guanine and cytosine, resulting in a highly biased codon usage. The IE gene region possesses 38 open reading frames (ORFs) greater than 300 bp in length, 11 of which have coding regions of at least 100 amino acids (aa) following potential translation initiator codons. The largest ORF consists of 1487 codons (4461 bp) starting with the first ATG and would encode a protein of MW 155,000. TATA and CCAAT sequences as well as several potential cis-acting elements lie upstream to the major ORF. The deduced amino acid sequence for the 155,000 protein has a high degree of homology to the herpes simplex virus type 1 (HSV-1) ICP4 protein and its varicella-zoster virus (VZV) homolog. The regions of the EHV-1 IE protein that are homologous with these proteins correspond to the previously determined pattern of homology between the HSV and VZV IE polypeptides. However, there are are a number of differences within these broadly defined regions. It is therefore expected that this comparative study will facilitate the identification of functionally important residues within the amino acid sequence of IE proteins.

Regulation of thymidine kinase activity in mouse L cells biochemically transformed by varicella-zoster virus

Regulation of thymidine kinase (TK) activity was examined in L(O)c133 and L(H3) cells carrying varicella-zoster virus-TK gene. TK activity of L(O)c133 cells was similarly high in either medium but that of L(H3) cells was high in HAT medium and low in non-HAT medium. Cell growth was well correlated with TK activities of L(O)c133 and L(H3) cells in medium conditions. Regulation of the TK gene in L cells carrying the VZV-TK gene is discussed.

Virion and nonstructural polypeptides of human herpesvirus-6

Human herpesvirus-6 (HHV-6) was purified from HHV-6-infected mononuclear cells from cord blood or infected culture medium. Virion was found to have at least 29 polypeptides ranging from 280 to 30 kDa. Six polypeptides were identified in the envelope fraction. Twenty-five viral polypeptides were also identified in HHV-6 infected cells by immunoprecipitation with immune serum.

Mutational dissection of the HSV-1 immediate-early protein Vmw175 involved in transcriptional transactivation and repression

Vmw175 is one of five immediate-early (IE) proteins encoded by herpes simplex virus type-1 (HSV-1). It is required for the transcription of later classes of genes and for the accompanying repression of IE expression. Vmw175 has been shown to be a transactivator of transcription and also to autoregulate its own synthesis. We have made a large number of small, in-frame, insertion and deletion mutants of a plasmid-borne copy of the gene encoding Vmw175. Study of the activity of the resultant mutant polypeptides in transient transfection assays has defined the regions of the protein important for the repression of its own promoter, and for the transactivation of an HSV early promoter in synergy with another HSV IE protein, Vmw110. Large stretches of the protein are relatively unimportant for either function, while the regions most sensitive to disruption correlate to sequences conserved between Vmw175 and VZV 140K, the corresponding transactivating protein of Varicella-Zoster virus. The region from amino acids 275 to 490 is particularly important for both repression and transactivation, whereas that from around 840 to 1100 seems to be more important for transactivation than repression. The nuclear localization signal has been mapped to within residues 682-774.

Cell lines containing varicella-zoster virus open reading frame 62 and expressing the "IE" 175 protein complement ICP4 mutants of herpes simplex virus type 1

Vero cells were cotransfected with pSV2neo and a recombinant plasmid containing the varicella-zoster virus (VZV) open reading frame 62 (ORF62). Three neomycin-resistant cell lines were isolated and shown to complement two different ICP4 mutants (tsB21 and d120) of herpes simplex virus (HSV) type 1 (HSV-1). VZV-specific RNA could not be detected in these cell lines, but following infection with tsB21, a 4.3-kilobase VZV transcript was detected. This RNA increased in quantity when cells were infected in the presence of cycloheximide. A VZV-specific protein of 175 kilodaltons was detected in extracts of all three cell lines following infection with wild-type HSV-1 but not in uninfected cells. That VZV RNA and protein were detected only in HSV-1 infected cells suggests that a component of the HSV virion activates the expression of VZV ORF62. The increase in RNA expression seen in the presence of cycloheximide indicates that the protein encoded by VZV ORF62, "IE"175, may be autoregulatory. These data provide further evidence that VZV "IE"175 is the functional analog of the HSV ICP4.