In vitro and in vivo transcription initiation sites on the TK-encoding BamHI Q fragment of HSV-1 DNA

The herpes simplex virus host shutoff (vhs) RNase limits accumulation of double stranded RNA in infected cells: Evidence for accelerated decay of duplex RNA

The herpes simplex virus virion host shutoff (vhs) RNase destabilizes cellular and viral mRNAs and blunts host innate antiviral responses. Previous work demonstrated that cells infected with vhs mutants display enhanced activation of the host double-stranded RNA (dsRNA)-activated protein kinase R (PKR), implying that vhs limits dsRNA accumulation in infected cells. Confirming this hypothesis, we show that partially complementary transcripts of the UL23/UL24 and UL30/31 regions of the viral genome increase in abundance when vhs is inactivated, giving rise to greatly increased levels of intracellular dsRNA formed by annealing of the overlapping portions of these RNAs. Thus, vhs limits accumulation of dsRNA at least in part by reducing the levels of complementary viral transcripts. We then asked if vhs also destabilizes dsRNA after its initial formation. Here, we used a reporter system employing two mCherry expression plasmids bearing complementary 3’ UTRs to produce defined dsRNA species in uninfected cells. The dsRNAs are unstable, but are markedly stabilized by co-expressing the HSV dsRNA-binding protein US11. Strikingly, vhs delivered by super-infecting HSV virions accelerates the decay of these pre-formed dsRNAs in both the presence and absence of US11, a novel and unanticipated activity of vhs. Vhs binds the host RNA helicase eIF4A, and we find that vhs-induced dsRNA decay is attenuated by the eIF4A inhibitor hippuristanol, providing evidence that eIF4A participates in the process. Our results show that a herpesvirus host shutoff RNase destabilizes dsRNA in addition to targeting partially complementary viral mRNAs, raising the possibility that the mRNA destabilizing proteins of other viral pathogens dampen the host response to dsRNA through similar mechanisms.

Essentially all viruses produce double-stranded RNA (dsRNA) during infection. Host organisms therefore deploy a variety of dsRNA receptors to trigger innate antiviral defenses. Not surprisingly, viruses in turn produce an array of antagonists to block this host response. The best characterized of the viral antagonists function by binding to and masking dsRNA and/or blocking downstream signaling events. Other less studied viral antagonists appear to function by reducing the levels of dsRNA in infected cells, but exactly how they do so remains unknown. Here we show that one such viral antagonist, the herpes simplex virus vhs ribonuclease, reduces dsRNA levels in two distinct ways. First, as previously suggested, it dampens the accumulation of partially complementary viral mRNAs, reducing the potential for generating dsRNA. Second, it helps remove dsRNA after its formation, a novel and surprising activity of a protein best known for its activity on single-stranded mRNA. Many other viral pathogens produce proteins that target mRNAs for rapid destruction, and it will be important to determine if these also limit host dsRNA responses in similar ways.

Characterization of the genes encoding UL24, TK and gH proteins from duck enteritis virus (DEV): a proof for the classification of DEV

Duck enteritis virus (DEV) is classified to the family Herpesviridae, but has not been grouped into any genus so far. Four overlapped fragments were amplified from the DEV genome with polymerase chain reaction (PCR). The assembled length of the four fragments was 6,202 bp, which contained the genes encoding unique long (UL) 24, thymidine kinase (TK) and glycoprotein H (gH) proteins. The UL24 overlapped with TK by 64 nucleotides (nt), in a head-to-head transcription orientation, and the TK and gH had the same transcription orientation. The comparison of amino acid sequences of these 3 deduced DEV proteins with other 12 alphaherpesviruses displayed 5 highly conserved sites in the UL24, as well as another 5 consensus regions in the TK and 4 consensus regions in the gH. The RNA polymerase II transcriptional control elements were identified in all the UL24, TK and gH of DEV. These elements included core promoters, TATA motifs and polyadenylation sites. Phylogenetic analysis for the genetic classification of DEV in the Alphaherpesvirinae subfamily with other 12 alphaherpesviruses was computed. The result showed that DEV was more closely related to avian herpesviruses, except infectious laryngotracheitis virus (ILTV), than to other alphaherpesviruses. Conclusively, according to the phylogenesis-based analysis and the homology comparison of functional domains of UL24, TK and gH, DEV should be classified to a separate genus of the Alphaherpesvirinae subfamily in the family Herpesviridae.

Identification, localization, and regulation of expression of the UL24 protein of herpes simplex virus type 1

The UL24 gene of herpes simplex virus type 1 is conserved across many herpesviruses, but its protein product has not been identified. We expressed the UL24 gene in insect cells from a recombinant baculovirus and used the resulting protein to raise a rat antiserum. In immunoblotting experiments, this antiserum recognized a 30-kDa protein in lysates from infected cells. The identity of this species as UL24 was confirmed by using a virus encoding a truncated form of UL24. On the basis of biochemical fractionation of infected cells, UL24 appeared to be predominantly nucleus associated, especially at later times in infection. Although certain UL24 transcripts exhibit early kinetics, UL24 protein accumulated at later times in infection and levels were decreased sixfold in the presence of the viral DNA synthesis inhibitor phosphonoacetic acid; thus, UL24 was expressed with leaky-late kinetics. The entire UL24 open reading frame is encoded by mRNAs with two different 5' ends. A mutation that eliminates the more abundant transcripts that originate at the first transcription start site resulted in a 10-fold reduction in the level of UL24 expressed but did not eliminate expression. Thus, the less abundant transcripts originating at the second transcription start site can evidently be translated, although transcripts originating at the first start site appear to be the major contributors to the expression of UL24. We conclude that UL24 is a bona fide herpes simplex virus type 1 protein that associates primarily with nuclei and whose expression is regulated at multiple levels.

Identification and characterization of the UL24 gene product of herpes simplex virus type 2

The UL24 gene of herpes simplex virus type 2 (HSV-2) is predicted to encode a 281 amino acid protein with a molecular mass of 30.5 kDa. In this study, the HSV-2 UL24 gene product has been identified by using a rabbit polyclonal antiserum produced against a recombinant protein containing the full-length UL24 gene product of HSV-2 fused to glutathione-S-transferase. The antiserum reacted specifically with a 32 kDa protein in HSV-2 186-infected Vero cells and with 31 and 32 kDa proteins in UL24-expressing Cos-7 cells. Accumulation of UL24 protein to detectable levels required viral DNA synthesis, indicating that the protein was regulated as a late gene. UL24 protein was found to be associated with purified HSV-2 virions and C capsids. Indirect immunofluorescence analysis demonstrated that the UL24-specific fluorescence was detected in perinuclear regions of the cytoplasm and/or in the nucleus as small discrete granules from 9h post infection (hpi). Furthermore, the UL24 protein expressed singly was detected predominantly in the nucleus and slightly in the cytoplasm at 24 h after transfection, with branch-like cytoplasmic protruding structures. Strong nucleolus staining was visible in partial cells.

Replication of herpes simplex virus type 1 within trigeminal ganglia is required for high frequency but not high viral genome copy number latency

The replication properties of a thymidine kinase-negative (TK(-)) mutant of herpes simplex virus type 1 (HSV-1) were exploited to examine the relative contributions of replication at the body surface and within trigeminal ganglia (TG) on the establishment of latent infections. The replication of a TK(-) mutant, 17/tBTK(-), was reduced by approximately 12-fold on the mouse cornea compared to the rescued isolate 17/tBRTK(+), and no replication of 17/tBTK(-) in the TG of these mice was detected. About 1.8% of the TG neurons of mice infected with 17/tBTK(-) harbored the latent viral genome compared to 23% of those infected with 17/tBRTK(+). In addition, the latent sites established by the TK(-) mutant contained fewer copies of the HSV-1 genome (average, 2.3/neuron versus 28/neuron). On the snout, sustained robust replication of 17tBTK(-) in the absence of significant replication within the TG resulted in a modest increase in the number of latent sites. Importantly, these latently infected neurons displayed a wild-type latent-genome copy number profile, with some neurons containing hundreds of copies of the TK(-) mutant genome. As expected, the replication of the TK(-) mutant appeared to be blocked prior to DNA replication in most ganglionic neurons in that (i) virus replication was severely restricted in ganglia, (ii) the number of neurons expressing HSV proteins was reduced 30-fold compared to the rescued isolate, (iii) cell-to-cell spread of virus was not detected within ganglia, and (iv) the proportion of infected neurons expressing late proteins was reduced by 89% compared to the rescued strain. These results demonstrate that the viral TK gene is required for the efficient establishment of latency. This requirement appears to be primarily for efficient replication within the ganglion, which leads to a sixfold increase in the number of latent sites established. Further, latent sites with high genome copy number can be established in the absence of significant virus genome replication in neurons. This suggests that neurons can be infected by many HSV virions and still enter the latent state.

The role of herpes simplex virus ICP27 in the regulation of UL24 gene expression by differential polyadenylation

Herpes simplex virus specifies two sets of transcripts from the UL24 gene, short transcripts (e.g., 1.4 kb), processed at the UL24 poly(A) site, and long transcripts (e.g., 5.6 kb), processed at the UL26 poly(A) site. The 1.4- and 5.6-kb transcripts initiate from the same promoter but are expressed with early and late kinetics, respectively. Measurements of transcript levels following actinomycin D treatment of infected cells revealed that the 1.4- and 5.6-kb UL24 transcripts have similar stabilities, consistent with UL24 transcript kinetics being regulated by differential polyadenylation rather than by differential stabilities. Although the UL24 poly(A) site, which gives rise to short transcripts, is encountered first during processing, long transcripts processed at the UL26 site are equally or more abundant; thus, operationally, the UL24 site is weak. Using a series of viral ICP27 mutants, we investigated whether ICP27, which has been suggested to stimulate the usage of weak poly(A) sites, stimulates 1.4-kb transcript accumulation. We found that accumulation of 1.4-kb transcripts did not require ICP27 during viral infection. Rather, ICP27 was required for full expression of 5.6-kb transcripts, and the decrease in 5. 6-kb transcripts relative to 1.4-kb transcripts was not due solely to reduced DNA synthesis. Our results indicate that temporal expression of UL24 transcripts can be regulated by differential polyadenylation and that although ICP27 is not required for processing at the operationally weak UL24 poly(A) site, it does modulate 5.6-kb transcript levels at a step subsequent to transcriptional initiation.

The BamHI fragment 9 of pseudorabies virus contains genes homologous to the UL24, UL25, UL26, and UL 26.5 genes of herpes simplex virus type 1

The genomes of pseudorabies virus (PrV) and of herpes simplex virus type 1 (HSV1) are colinear, excepting an inversion in the unique long region, of which one extremity resides within the BamHI fragment 9. This fragment (4088 bp) encodes the counterparts of HSV1 UL24, UL25, UL26 and UL26.5 that are transcribed into four 3'-coterminal mRNAs. Multiple alignments of UL24, UL25 and UL26 protein homologs from alpha-, beta- and gamma-herpesviruses were performed. The PrV UL24 protein is shorter than its counterparts, missing the non-conserved COOH-terminal region. The region which is common to all viruses contains a basic NH2-terminus and a hydrophobic COOH-end, suggesting that UL24 may function as a matrix protein. The UL25 proteins are well conserved, particularly among the alpha-herpesviruses. All the domains involved in the proteolytic activity of theUL26 protein are highly conserved, as well as the two cleavage sites. Thus, its function and processing may be similar in PrV as in other herpesviruses. Due to the fact that in PrV the UL26 and UL44 genes are adjacent and their ends are conserved, the right border of the inversion must lie within their intergenic region.

Regulation of herpes simplex virus thymidine kinase in cells treated with a synergistic antiviral combination of alpha interferon and acyclovir

Alpha interferon (IFN-alpha) and acyclovir (ACV) are synergistic in their anti-herpes simplex virus activities. IFN-alpha treatment reduced the herpes simplex virus thymidine kinase (TK) activity present in cells 6 h postinfection, while steady-state levels of TK mRNA remained at or above the amount in infected, untreated cells. The inhibition of TK production by IFN-alpha treatment appeared to be transient and translational, not transcriptional.

Isolation of a herpes simplex virus type 1 mutant with a deletion in the virion host shutoff gene and identification of multiple forms of the vhs (UL41) polypeptide

The virion host shutoff (vhs) gene (UL41) of herpes simplex virus type 1 (HSV-1) encodes a virion component that induces degradation of host mRNAs and the shutoff of most host protein synthesis. Subsequently, the vhs protein accelerates the turnover of all kinetic classes of viral mRNA. To identify the vhs (UL41) polypeptide within infected cells and virions, antisera raised against a UL41-lacZ fusion protein were used to characterize the polypeptides encoded by wild-type HSV-1 and two mutants: vhs1, a previously characterized mutant that lacks detectable virion host shutoff activity, and vhs-delta Sma, a newly constructed mutant containing a deletion of 196 codons from UL41. Two forms of the vhs (UL41) polypeptide were identified in cells infected with the wild-type virus or vhs1. Wild-type HSV-1 produced a major 58-kDa polypeptide, as well as a less abundant 59.5-kDa form of the protein, while vhs1 produced 57- and 59-kDa polypeptides that were approximately equally abundant. Although for either virus, both forms of the protein were phosphorylated, they differed in the extent of phosphorylation. While both vhs polypeptides were found in infected cells, only the faster migrating, less phosphorylated form was incorporated into virions. vhs-delta Sma encoded a smaller, 31-kDa polypeptide which, although present in infected cells, was not incorporated into virions. The results identify multiple forms of the vhs (UL41) polypeptide and suggest that posttranslational processing affects its packaging into virions, as well as its ability to induce mRNA degradation.

Herpes simplex virus thymidine kinase and specific stages of latency in murine trigeminal ganglia

From marker rescue, sequencing, transcript, and latency analyses of the thymidine kinase-negative herpes simplex virus mutant dlsactk and studies using the thymidine kinase inhibitor Ro 31-5140, we infer that the virus-encoded thymidine kinase is required in murine trigeminal ganglia for acute replication and lytic gene expression, for increasing the numbers of cells expressing latency-associated transcripts, and for reactivation from latent infection.

Replication, latent infection, and reactivation in neuronal culture with a herpes simplex virus thymidine kinase-negative mutant

Herpes simplex virus type 1 (HSV-1) mutant viruses lacking functional viral thymidine kinase activity are reported to be incapable of replication in neurons. To investigate the role of viral thymidine kinase (TK) activity in the HSV-1 infection of the neuron, we studied a thymidine kinase-negative (TK-) mutant virus engineered to eliminate TK function without affecting the other known transcripts encoded in this region of the genome. Studies using the mouse eye model demonstrated that the mutant behaved as is reported for other TK- viruses: DNA of the mutant virus was detected in the ganglia during the latent infection by polymerase chain reaction, but virus did not reactivate after explantation of the ganglia. Utilizing the neuronal cultures, we investigated the ability of the mutant virus to replicate in neurons and the capacity of the mutant virus to establish latency and reactivate. With a low multiplicity of infection (m.o.i.), replication of the TK- mutant virus in sensory neurons in culture was significantly delayed compared to that of the wild-type virus. However, when a high m.o.i. was used, the mutant and the wild-type viruses replicated with similar kinetics. The TK- mutant virus was capable of establishment of latency and reactivation from the latent infection in sensory neurons in culture. These data suggest that HSV-1 thymidine kinase activity facilitates viral replication, but that TK activity is not essential for either replication or reactivation from latent infections in neurons in vitro.

Regulation of herpes simplex virus true late gene expression: sequences downstream from the US11 TATA box inhibit expression from an unreplicated template

The true late genes of herpes simplex virus type 1 (HSV-1) are expressed only after the onset of viral DNA replication. Previous studies demonstrated that late promoters lack elements upstream of the TATA box and suggested that only a subset of TATA elements can function in the context of true late promoters. We determined which structural features of true late promoters are responsible for the stringent requirement for viral DNA replication by inserting a series of simple model constructs into the HSV-1 genome in place of one of the two promoters of the UL24 gene. An oligonucleotide consisting of 19 nucleotides spanning the TATA box of the HSV-1 true late US11 gene drove barely detectable levels of expression; by contrast, the corresponding regions of the Adenovirus type 2 major late promoter and the HSV-1 true late glycoprotein C promoter were much more active. Transcripts driven from all of these minimal TATA box promoters accumulated without viral DNA replication. The activity of the US11 TATA box was stimulated by adding upstream Sp1-binding sites or placing the US11 or rabbit beta-globin cap/leader region (-11 to +39) downstream. The Sp1-TATA and TATA-beta-globin cap/leader constructs remained replication independent, while the TATA-US11 cap/leader promoter displayed true late regulation. These results demonstrate that sequences located within the US11 cap/leader region impose a strict requirement for viral DNA replication on a minimal TATA box promoter.

Phenotypic and genotypic characterization of locus Syn 5 in herpes simplex virus 1

Previous papers have reported that the syncytial mutant HSV-1(13)S11 carries three segregable syn mutations and exhibits its altered phenotype in four different cell lines, i.e. HEp-2, VERO, BHK and HEL both at 34 degrees C and 39 degrees C. Those studies have shown that one of three syncytial loci, designated Syn 5, is located in the Bam HI Q fragment spanning map units 0.296-0.317 of the prototype arrangement. Recombinants obtained from marker transfer experiments with donor BamHI Q fragment, have shown that locus Syn 5 is able to induce cell-to-cell fusion in VERO, BHK and HEL but not in HEp-2 cells. In this paper we have characterized the syn mutant HSV-1(13)S11 with regard to plaque morphology, synthesis of viral polypeptides and glycoproteins, thymidine kinase activity and physical map position of locus Syn 5 on the genome. Pertinent to the syn phenotype, earlier papers claimed that two different polypeptides, thymidine kinase (TK) and glycoprotein H (gH), whose genes map in BamHI Q, may be responsible for the fusion activity. Functional studies on the TK of the syn mutant HSV-1(13)S11 indicate that this polypeptide accumulates normally in infected cells and is a fully active enzyme. The other gene product, gH, has been studied with SDS-PAGE and in radioimmunoprecipitation (RIP) experiments using specific monoclonal antibodies. The results indicate that the amount of gH accumulation in the syn mutant-infected cells is greater than its parental strain. However, new marker transfer experiments described here located locus Syn 5 in 663 base pairs between SstI and EcoRI restriction endonuclease sites at the right end of the BamHI Q fragment, where TK gene overlaps in opposite orientation with UL 24 gene. Altogether these results indicate that the Syn 5 locus segregates from the gene specifying gH, to a region encompassing portions of the TK and UL 24 genes, and that the syn mutation does not affect the expression or activity of TK.

Analysis of the thymidine kinase gene from clinically isolated acyclovir-resistant herpes simplex viruses

The isolation and description of acyclovir-resistant (ACVR) herpes simplex-2 viruses from patients with AIDS has recently been reported. These ACVR viruses were all markedly decreased in their thymidine kinase (TK) activity, and 6 of 10 of these TK viruses were able to establish latency. In addition, one of these isolates, ACVR-86012 was neuropathogenic in a murine encephalitis model. In this paper, the characteristics of these isolates with respect to TK polypeptide synthesis are examined. All but one isolate synthesized a detectable TK protein by immunoprecipitation, and 9/10 of the TK proteins had an altered electrophoretic mobility as compared to wild-type. The TK polypeptide from the neuropathogenic isolate ACVR-86012 was full-length and the gene was sequenced. An amino acid change from a glutamine to a proline at amino acid residue 105 was detected compared to the wild-type HSV-333 strain. These results indicate that an amino acid change in the NH2 portion of the TK protein is associated with a full-length peptide with decreased enzyme activity but the virus retains neuropathic virulence.

In vitro mRNA degradation system to study the virion host shutoff function of herpes simplex virus

The virion host shutoff (vhs) gene of herpes simplex virus encodes a virion polypeptide that induces degradation of host mRNAs at early times and rapid turnover of viral mRNAs throughout infection. To better investigate the vhs function, an in vitro mRNA degradation system was developed, consisting of cytoplasmic extracts from HeLa cells infected with wild-type herpes simplex virus type 1 or a mutant encoding a defective vhs polypeptide. Host and viral mRNAs were degraded rapidly in extracts from cells productively infected with wild-type herpes simplex virus type 1 but not in extracts from mock-infected cells or cells infected with the mutant vhs1. In contrast, 28S rRNA was stable in all three kinds of extract. Accelerated turnover of host mRNAs was also observed in extracts from cells infected with wild-type virus in the presence of dactinomycin, indicating that the activity was induced by a structural component of the infecting virions. The in vitro vhs activity was inactivated by heat or proteinase K digestion but was insensitive to brief treatment of the extracts with micrococcal nuclease. It was not inhibited by placental RNase inhibitor, it exhibited a strong dependence upon added Mg2+, it was active at concentrations of K+ up to 200 mM, and it did not require the components of an energy-generating system. In summary, the in vitro mRNA degradation system appears to accurately reproduce the vhs-mediated decay of host and viral mRNAs and should be useful for studies of the mechanism of vhs action.

A conserved open reading frame that overlaps the herpes simplex virus thymidine kinase gene is important for viral growth in cell culture

Of 18 mutants containing clustered point mutations within UL24 (an open reading frame that overlaps the herpes simplex virus thymidine kinase gene on the opposite strand), 15 formed small plaques and were substantially impaired for virus growth in cell culture. Mutations conferring the small plaque phenotype disrupt regions of UL24 that share considerable sequence similarity with open reading frames common to herpesviruses of mammals and birds. We infer that UL24 is expressed and important for virus growth in cell culture and suggest that possible effects on UL24 should be considered in studies of thymidine kinase-deficient mutants.

Effect of an amber mutation in the herpes simplex virus thymidine kinase gene on polypeptide synthesis and stability

KG111 is a mutant of herpes simplex virus (HSV), strain KOS, that exhibits temperature-dependent drug resistance. For example, it is almost as resistant as a thymidine kinase (tk)-deficient virus at 39 degrees, but is relatively sensitive to acyclovir at 34 degrees, Using marker transfer techniques, we have mapped the mutation conferring temperature-dependent drug resistance in KG111 to the 5' portion of the tk gene. Sequencing of this region revealed an amber mutation at codon 44, which lies between the first and second methionine codons of the tk polypeptide. This mutation is identical to that found in TK4, an HSV mutant derived from Cl 101 (L. Haarr et al., 1985, J. Virol. 56, 512-519). Analyses of immunoprecipitated tk proteins from KG111- and TK4-infected cells showed that KG111 and TK4 do not synthesize full-length tk polypeptides, but instead produce a truncated form of the protein. Small amounts of a similar truncated tk polypeptide are also produced in wild-type-infected cells and are thought to arise from initiation at a downstream AUG. The relative amounts and size of the mutant tk proteins compared with those of the wild-type are consistent with the amber mutation eliminating translation of full-length polypeptide and causing a four- to fivefold increase in the utilization of downstream AUG codons for initiation. The truncated polypeptides specified by KG111 and TK4 are less stable than the full-length polypeptide at 39 degrees, which may contribute to the conditional drug-resistant phenotype. On the other hand, the truncated polypeptides normally expressed by wild-type virus at low levels and the more highly expressed truncated tk polypeptides from a deletion mutant are relatively stable at 39 degrees. These results suggest that stability of the truncated tk polypeptide is influenced by the amount of tk present.

A herpes simplex virus type 1 mutant resistant to benzhydrazone, an inhibitor of glycoprotein synthesis in herpesvirus-infected cells. Preliminary mapping of benzhydrazone-resistance and of a novel syncytial mutation

Benzhydrazone (BH) is an inhibitor of glycoprotein biosynthesis. It acts selectively in Herpes simplex virus (HSV)-infected cells and does not significantly affect glycoprotein synthesis in uninfected cells and in cells infected with other viruses. Previously, we reported on a syncytial (syn) mutant, designated HSV-1(13)S11, resistant to BH, and showed that BH-resistance is encoded in the mutant virus DNA and therefore can be transferred into the genome of wild type HSVs. The present paper reports on a preliminary mapping in HSV-1(13)S11 genome of the loci which confer resistance to BH and of three distinct syn mutations present simultaneously in this mutant. Two of them were mapped in previously described syn loci localized in BamHI fragment L (map units 0.707-0.745) (locus syn 1) and BamHI fragment Q (map units 0.296-0.317) (locus syn 5). A third mutation not described before and mapping in BamHI fragment SP (c.a. map units 0.81-0.85) conferred the syn phenotype to both HEp-2 and Vero cells. This novel mutation has been designated herein locus syn 6. Transfer of BH-resistance could be achieved in cotransfection experiments involving two HSV-1(13)S11 fragments, BamHIL and BamHISP.

The properties and sequence of glycoprotein H of herpes simplex virus type 1

The map position of the coding sequence of glycoprotein H of herpes simplex virus type 1 was determined by marker transfer studies in which DNA fragments cloned from a virus resistant to neutralisation by an anti-gH monoclonal antibody were used to transfer antibody resistance to wild type virus DNA following cotransfection. The gH coding sequence was mapped to the BglII "m" fragment of HSV-1 DNA (map coordinates 0.27-0.312), confirming the map position previously determined by intertypic recombinant analysis (Buckmaster et al., 1984). The complete nucleotide sequence of the BglII "m" fragment revealed two large open reading frames in addition to the thymidine kinase gene. The open reading frame lying immediately 3' of the thymidine kinase gene has a predicted translation product with the features of a large glycoprotein. This open reading frame translates to an amino acid sequence of 90,323 mol wt with a signal peptide, a membrane anchor sequence, a large external domain containing potential N-glycosylation sites, and a charged C- terminal cytoplasmic domain. We suppose that this amino acid sequence corresponds to gH of HSV-1, and A. Davison (personal communication) has noted the existence of homologous glycoproteins predicted from the nucleotide sequences of Varicella-zoster virus and Epstein-Barr virus. The properties of monoclonal antibody LP11, directed against gH show remarkable similarities to the properties for gD antibodies. LP11 efficiently neutralizes virus infectivity, blocks cell fusion by syncytial virus strains, and inhibits the formation of plaques when added to cell monolayers after infection. These similarities in antibody activity imply functional relatedness between gH and gD of herpes simplex virus.

Establishment of latency in mice by herpes simplex virus 1 recombinants that carry insertions affecting regulation of the thymidine kinase gene

Herpes simplex virus 1 recombinants carrying alpha-, beta-, and late gamma (gamma 2)-regulated thymidine kinase (TK) genes were tested for the ability to establish latency in BALB/c mice inoculated by the eye route. The significant findings were as follows. Representatives of alpha- and gamma 2-regulated TK recombinants all established and maintained latent infections, but the efficiency was somewhat lower than that of wild-type virus. Of the three alpha TK recombinants tested, one (R316) spontaneously deleted portions of the inserted sequences which conferred alpha regulation to the TK gene. The viruses carrying these deletions expressed considerably lower TK activity than did wild-type virus, i.e., 2 to 40% of the levels expressed by the wild-type virus carrying the beta TK gene. However, the ability of these viruses to establish latency was not related to the efficiency of expression of the TK gene. These results indicate the following: (i) conversion of the TK gene into an alpha or gamma 2 gene did not preclude the establishment of latent infections; (ii) there was no correlation between the levels of TK activity expressed in cell culture and the ability to establish latency; and (iii) rearrangement of the genome by insertions or deletions which interrupt gene domains did not automatically result in an inability to establish latent infections.