The deoxyribonuclease induced after infection of KB cells by herpes simplex virus type 1 or type 2. I. Purification and characterization of the enzyme

Screening and identification of emodin as an EBV DNase inhibitor to prevent its biological functions

BACKGROUND

The Epstein-Barr virus (EBV) is a prevalent oncovirus associated with a variety of human illnesses. BGLF5, an EBV DNase with alkaline nuclease (AN) activity, plays important roles in the viral life cycle and progression of human malignancies and has been suggested as a possible diagnostic marker and target for cancer therapy. Methods used conventionally for the detection of AN activity, radioactivity-based nuclease activity assay and DNA digestion detection by gel electrophoresis, are not suitable for screening AN inhibitors; the former approach is unsafe, and the latter is complicated. In the present study, a fluorescence-based nuclease activity assay was used to screen several natural compounds and identify an EBV DNase inhibitor.

RESULTS

Fluorescence-based nuclease activity assays, in which the DNA substrate is labelled with PicoGreen dye, are cheaper, safer, and easier to perform. Herein, the results of the fluorescence-based nuclease activity assay were consistent with the results of the two conventional methods. In addition, the PicoGreen-labelling method was applied for the biochemical characterisation of viral nucleases. Using this approach, we explored EBV DNase inhibitors. After several rounds of screening, emodin, an anthraquinone derivative, was found to possess significant anti-EBV DNase activity. We verified the efficacy of emodin using the conventional DNA-cleavage assay. Furthermore, using comet assay and micronucleus formation detection, we confirmed that emodin can inhibit DNase-induced DNA damage and genomic instability. Additionally, emodin treatment inhibited EBV production.

CONCLUSIONS

Using a PicoGreen-mediated nuclease activity assay, we successfully demonstrated that emodin has the potential to inhibit EBV DNase nuclease activity. Emodin also inhibits EBV DNase-related biological functions, suggesting that it is a potential inhibitor of EBV DNase.

Anti-cytomegalovirus activity of the anthraquinone atanyl blue PRL

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The anthraquinone atanyl blue PRL inhibits human cytomegalovirus replication.

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The block to viral replication appears early after entry and substantially reduces viral immediate early gene expression.

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In vitro, atanyl blue PRL inhibits the nuclease activity of purified viral alkaline nuclease, UL98.

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The antiviral activity of atanyl blue PRL may be manifested through inhibition of UL98’s nuclease activity.

Human cytomegalovirus (CMV) causes significant disease in immunocompromised patients and serious birth defects if acquired in utero. Available CMV antivirals target the viral DNA polymerase, have significant toxicities, and suffer from resistance. New drugs targeting different pathways would be beneficial. The anthraquinone emodin is proposed to inhibit herpes simplex virus by blocking the viral nuclease. Emodin and related anthraquinones are also reported to inhibit CMV. In the present study, emodin reduced CMV infectious yield with an EC₅₀ of 4.9 μM but was cytotoxic at concentrations only twofold higher. Related anthraquinones acid blue 40 and alizarin violet R inhibited CMV at only high concentrations (238–265 μM) that were also cytotoxic. However, atanyl blue PRL inhibited infectious yield of CMV with an EC₅₀ of 6.3 μM, significantly below its 50% cytotoxic concentration of 216 μM. Atanyl blue PRL reduced CMV infectivity and inhibited spread. When added up to 1 h after infection, it dramatically reduced CMV immediate early protein expression and blocked viral DNA synthesis. However, it had no antiviral activity when added 24 h after infection. Interestingly, atanyl blue PRL inhibited nuclease activities of purified CMV UL98 protein with IC₅₀ of 4.5 and 9.3 μM. These results indicate that atanyl blue PRL targets very early post-entry events in CMV replication and suggest it may act through inhibition of UL98, making it a novel CMV inhibitor. This compound may provide valuable insights into molecular events that occur at the earliest times post-infection and serve as a lead structure for antiviral development.

Recombination promoted by DNA viruses: phage λ to herpes simplex virus

The purpose of this review is to explore recombination strategies in DNA viruses. Homologous recombination is a universal genetic process that plays multiple roles in the biology of all organisms, including viruses. Recombination and DNA replication are interconnected, with recombination being essential for repairing DNA damage and supporting replication of the viral genome. Recombination also creates genetic diversity, and viral recombination mechanisms have important implications for understanding viral origins as well as the dynamic nature of viral-host interactions. Both bacteriophage λ and herpes simplex virus (HSV) display high rates of recombination, both utilizing their own proteins and commandeering cellular proteins to promote recombination reactions. We focus primarily on λ and HSV, as they have proven amenable to both genetic and biochemical analysis and have recently been shown to exhibit some surprising similarities that will guide future studies.

Coordinated destruction of cellular messages in translation complexes by the gammaherpesvirus host shutoff factor and the mammalian exonuclease Xrn1

Several viruses encode factors that promote host mRNA degradation to silence gene expression. It is unclear, however, whether cellular mRNA turnover pathways are engaged to assist in this process. In Kaposi's sarcoma-associated herpesvirus this phenotype is enacted by the host shutoff factor SOX. Here we show that SOX-induced mRNA turnover is a two-step process, in which mRNAs are first cleaved internally by SOX itself then degraded by the cellular exonuclease Xrn1. SOX therefore bypasses the regulatory steps of deadenylation and decapping normally required for Xrn1 activation. SOX is likely recruited to translating mRNAs, as it cosediments with translation initiation complexes and depletes polysomes. Cleaved mRNA intermediates accumulate in the 40S fraction, indicating that recognition occurs at an early stage of translation. This is the first example of a viral protein commandeering cellular mRNA turnover pathways to destroy host mRNAs, and suggests that Xrn1 is poised to deplete messages undergoing translation in mammalian cells.

Viruses use a number of strategies to commandeer host machinery and create an optimal environment for their replication. One strategy employed by oncogenic gammaherpesviruses such as Kaposi's sarcoma-associated herpesvirus (KSHV) is to block cellular gene expression through extensive destruction of mRNAs. A single viral protein called SOX is sufficient to drive this phenotype, but the mechanism by which it does so has remained unclear. Here we show that host mRNA destruction is the result of the coordinated action of SOX and a cellular RNA degrading enzyme, Xrn1. By cleaving mRNAs internally, SOX recruits the activity of Xrn1 while bypassing the regulatory mechanisms that normally prevent this enzyme from prematurely degrading mRNAs. We also find that SOX co-sediments with translation complexes, and specifically targets mRNAs for cleavage at an early stage of translation. We hypothesize this allows the virus to selectively target mRNAs, thereby liberating host gene expression machinery. Collectively, these findings describe a novel interplay between the gammaherpesvirus SOX protein and cellular degradation machinery, and shed light on how a single viral component can hijack cellular machinery to efficiently destroy messages.

Structural modelling and mutagenesis of human cytomegalovirus alkaline nuclease UL98

Human cytomegalovirus encodes an alkaline nuclease, UL98, that is highly conserved among herpesviruses and has both endonuclease (endo) and exonuclease (exo) activities. This protein is thought to be important for viral replication and therefore represents a potential target for antiviral development; however, little is known about its structure or role in viral replication. Comparative structural modelling was used to build a model of UL98 based on the known structure of shutoff and exonuclease protein from Kaposi's sarcoma-associated herpesvirus. The model predicts that UL98 residues D254, E278 and K280 represent the critical aspartic acid, glutamic acid and lysine active-site residues, respectively, while R164 and S252 correspond to residues proposed to bind the 5' phosphate of the DNA substrate. UL98 with an amino-terminal hexahistidine tag was expressed in Escherichia coli, purified by affinity chromatography and confirmed to have exo and endo activities. Amino acid substitutions D254A, E278A, K280A and S252A virtually eliminated exo and endo activities, whereas R164A retained full endo activity but only 10 % of the exo activity compared with the wild-type enzyme. A mutant virus lacking UL98 was viable but severely attenuated for replication, while one expressing UL98(R164A) replicated normally. These results confirm the utility of the model in representing the active-site region of UL98 and suggest a mechanism for the differentiation of endonuclease and exonuclease activities. These findings could facilitate the exploration of the roles of alkaline nucleases in herpesvirus replication and the rational design of inhibitors that target their enzymic activities.

Crystal structure of a KSHV-SOX-DNA complex: insights into the molecular mechanisms underlying DNase activity and host shutoff

The early lytic phase of Kaposi’s sarcoma herpesvirus infection is characterized by viral replication and the global degradation (shutoff) of host mRNA. Key to both activities is the virally encoded alkaline exonuclease KSHV SOX. While the DNase activity of KSHV SOX is required for the resolution of viral genomic DNA as a precursor to encapsidation, its exact involvement in host shutoff remains to be determined. We present the first crystal structure of a KSHV SOX–DNA complex that has illuminated the catalytic mechanism underpinning both its endo and exonuclease activities. We further illustrate that KSHV SOX, similar to its Epstein–Barr virus homologue, has an intrinsic RNase activity in vitro that although an element of host shutoff, cannot solely account for the phenomenon.

Processing of lagging-strand intermediates in vitro by herpes simplex virus type 1 DNA polymerase

The processing of lagging-strand intermediates has not been demonstrated in vitro for herpes simplex virus type 1 (HSV-1). Human flap endonuclease-1 (Fen-1) was examined for its ability to produce ligatable products with model lagging-strand intermediates in the presence of the wild-type or exonuclease-deficient (exo(-)) HSV-1 DNA polymerase (pol). Primer/templates were composed of a minicircle single-stranded DNA template annealed to primers that contained 5' DNA flaps or 5' annealed DNA or RNA sequences. Gapped DNA primer/templates were extended but not significantly strand displaced by the wild-type HSV-1 pol, although significant strand displacement was observed with exo(-) HSV-1 pol. Nevertheless, the incubation of primer/templates containing 5' flaps with either wild-type or exo(-) HSV-1 pol and Fen-1 led to the efficient production of nicks that could be sealed with DNA ligase I. Both polymerases stimulated the nick translation activity of Fen-1 on DNA- or RNA-containing primer/templates, indicating that the activities were coordinated. Further evidence for Fen-1 involvement in HSV-1 DNA synthesis is suggested by the ability of a transiently expressed green fluorescent protein fusion with Fen-1 to accumulate in viral DNA replication compartments in infected cells and by the ability of endogenous Fen-1 to coimmunoprecipitate with an essential viral DNA replication protein in HSV-1-infected cells.

Nucleolin is required for efficient nuclear egress of herpes simplex virus type 1 nucleocapsids

Herpesvirus nucleocapsids assemble in the nucleus and must cross the nuclear membrane for final assembly and maturation to form infectious progeny virions in the cytoplasm. It has been proposed that nucleocapsids enter the perinuclear space by budding through the inner nuclear membrane, and these enveloped nucleocapsids then fuse with the outer nuclear membrane to enter the cytoplasm. Little is known about the mechanism(s) for nuclear egress of herpesvirus nucleocapsids and, in particular, which, if any, cellular proteins are involved in the nuclear egress pathway. UL12 is an alkaline nuclease encoded by herpes simplex virus type 1 (HSV-1) and has been suggested to be involved in viral DNA maturation and nuclear egress of nucleocapsids. Using a live-cell imaging system to study cells infected by a recombinant HSV-1 expressing UL12 fused to a fluorescent protein, we observed the previously unreported nucleolar localization of UL12 in live infected cells and, using coimmunoprecipitation analyses, showed that UL12 formed a complex with nucleolin, a nucleolus marker, in infected cells. Knockdown of nucleolin in HSV-1-infected cells reduced capsid accumulation, as well as the amount of viral DNA resistant to staphylococcal nuclease in the cytoplasm, which represented encapsidated viral DNA, but had little effect on these viral components in the nucleus. These results indicated that nucleolin is a cellular factor required for efficient nuclear egress of HSV-1 nucleocapsids in infected cells.

Crystal structure of the shutoff and exonuclease protein from the oncogenic Kaposi's sarcoma-associated herpesvirus

The Kaposi's sarcoma-associated herpesvirus protein SOX (shut off and exonuclease) and its Epstein-Barr virus homolog, BGLF5, are active during the early lytic phase and belong to the alkaline nuclease family. Both proteins have been shown to be bifunctional, being responsible for DNA maturation as well as host shutoff at the mRNA level. We present the crystal structure of SOX determined at 1.85 A resolution. By modeling DNA binding, we have identified catalytic residues that explain the preferred 5'-exonuclease activity of the alkaline nucleases. The presence of a crevice suitable for binding duplex DNA supports a role for herpes alkaline nucleases in recombination events preceding packaging of viral DNA. Direct interaction with dsDNA is supported by oligonucleotide binding data. Mutations specifically affecting host shutoff map to a surface region of the N-terminal domain, implying an essential role in protein-protein interactions, and link the RNase activity of the enzyme to mRNA degradation pathways.

Herpes simplex virus UL12.5 targets mitochondria through a mitochondrial localization sequence proximal to the N terminus

The herpes simplex virus type 1 (HSV-1) gene UL12 encodes a conserved alkaline DNase with orthologues in all herpesviruses. The HSV-1 UL12 gene gives rise to two separately promoted 3' coterminal mRNAs which encode distinct but related proteins: full-length UL12 and UL12.5, an amino-terminally truncated form that initiates at UL12 codon 127. Full-length UL12 localizes to the nucleus where it promotes the generation of mature viral genomes from larger precursors. In contrast, UL12.5 is predominantly mitochondrial and acts to trigger degradation of the mitochondrial genome early during infection. We examined the basis for these very different subcellular localization patterns. We confirmed an earlier report that the amino-terminal region of full-length UL12 is required for nuclear localization and provide evidence that multiple nuclear localization determinants are present in this region. In addition, we demonstrate that mitochondrial localization of UL12.5 relies largely on sequences located between UL12 residues 185 and 245 (UL12.5 residues 59 to 119). This region contains a sequence that resembles a typical mitochondrial matrix localization signal, and mutations that reduce the positive charge of this element severely impaired mitochondrial localization. Consistent with matrix localization, UL12.5 displayed a detergent extraction profile indistinguishable from that of the matrix protein cyclophilin D. Mitochondrial DNA depletion required the exonuclease activity of UL12.5, consistent with the idea that UL12.5 located within the matrix acts directly to destroy the mitochondrial genome. These results clarify how two highly related viral proteins are targeted to different subcellular locations with distinct functional consequences.

Emodin is a novel alkaline nuclease inhibitor that suppresses herpes simplex virus type 1 yields in cell cultures

BACKGROUND AND PURPOSE

Most antiviral therapies directed against herpes simplex virus (HSV) infections are limited to a small group of nucleoside analogues that target the viral polymerase. Extensive clinical use of these drugs has led to the emergence of resistant viral strains, mainly in immunocompromised patients. This highlights the need for the development of new anti-herpesviral drugs with novel targets. Herein the effects of a plant anthraquinone, emodin, on the HSV-1 alkaline nuclease activity and virus yields were investigated.

EXPERIMENTAL APPROACH

HSV-1 alkaline nuclease activity was examined by nuclease activity assay. Inhibition of virus yields was measured by plaque reduction assay and immunohistochemical staining. Interaction between emodin and alkaline nuclease was analysed by docking technology.

KEY RESULTS

Emodin specifically inhibited the nuclease activity of HSV-1 UL12 alkaline nuclease in a biochemical assay. Plaque reduction assay revealed that emodin reduced the plaque formation with an EC(50) of 21.5+/-4.4 muM. Immunohistochemical staining using the anti-nucleocapsid protein antibody demonstrated that emodin induced the accumulation of viral nucleocapsids in the nucleus in a dose-dependent manner. Docking analysis further suggested that the inhibitory effect of emodin on the UL12 activity may result from the interaction between emodin and critical catalytic amino acid residues of UL12.

CONCLUSIONS AND IMPLICATIONS

Our findings suggest that emodin is a potent anti-HSV agent that inhibits the yields of HSV-1 via the suppression of a novel target, UL12.

Herpes simplex virus eliminates host mitochondrial DNA

Mitochondria have crucial roles in the life and death of mammalian cells, and help to orchestrate host antiviral defences. Here, we show that the ubiquitous human pathogen herpes simplex virus (HSV) induces rapid and complete degradation of host mitochondrial DNA during productive infection of cultured mammalian cells. The depletion of mitochondrial DNA requires the viral UL12 gene, which encodes a conserved nuclease with orthologues in all herpesviruses. We show that an amino-terminally truncated UL12 isoform-UL12.5-localizes to mitochondria and triggers mitochondrial DNA depletion in the absence of other HSV gene products. By contrast, full-length UL12, a nuclear protein, has little or no effect on mitochondrial DNA levels. Our data document that HSV inflicts massive genetic damage to a crucial host organelle and show a novel mechanism of virus-induced shutoff of host functions, which is likely to contribute to the cell death and tissue damage caused by this widespread human pathogen.

Herpes simplex virus type 1 single-strand DNA binding protein ICP8 enhances the nuclease activity of the UL12 alkaline nuclease by increasing its processivity

UL12 is a 5'- to 3'-exonuclease encoded by herpes simplex virus type 1 (HSV-1) which degrades single- and double-stranded DNA. UL12 and the single-strand DNA binding protein ICP8 mediate a strand exchange reaction. We found that ICP8 inhibited UL12 digestion of single-stranded DNA but stimulated digestion of double-stranded DNA threefold. The stimulatory effect of ICP8 was independent of a strand exchange reaction; furthermore, the effect was specific to ICP8, as it could not be reproduced by Escherichia coli single-stranded DNA binding protein. The effect of ICP8 on the rate of UL12 double-stranded DNA digestion is attributable to an increase in processivity in the presence of ICP8.

Replication, recombination and packaging of amplicon DNA in cells infected with the herpes simplex virus type 1 alkaline nuclease null mutant ambUL12

The alkaline nuclease (AN) encoded by gene UL12 of herpes simplex virus type 1 (HSV-1) is essential for efficient virus replication but its role during the lytic cycle remains incompletely understood. Inactivation of the UL12 gene results in reductions in viral DNA synthesis, DNA packaging, egress of DNA-containing capsids from the nucleus and ability of progeny virions to initiate new cycles of infection. Mechanistically, AN has been implicated in resolving branched structures in HSV-1 replicative intermediates prior to encapsidation, and promoting DNA strand-exchange. In this study, amplicons (bacterial plasmids containing functional copies of a virus replication origin and packaging signal) were used to analyse further the defects of the UL12 null mutant ambUL12. When ambUL12 was used as a helper virus both replication and packaging of the transfected amplicon were reduced in comparison with cells infected with wild-type (wt) HSV-1, and to extents similar to those previously observed for genomic ambUL12 DNA. By using amplicons differing at a specific restriction endonuclease site it was demonstrated that replicating molecules exhibit high frequency intermolecular recombination in both wt- and mutant-infected cells. Surprisingly, in the absence of the UL12 product, amplicons lacking a functional encapsidation signal were packaged. Moreover, these packaged molecules could be serially propagated indicating that they had been incorporated into functional virions. This difference in packaging specificity between wt HSV-1 and ambUL12 might indicate that replicative intermediates accumulating in the absence of AN contain an increased incidence of structures that can serve for the initiation of DNA packaging.

The UL12.5 gene product of herpes simplex virus type 1 exhibits nuclease and strand exchange activities but does not localize to the nucleus

The herpes simplex virus type 1 (HSV-1) alkaline nuclease, encoded by the UL12 gene, plays an important role in HSV-1 replication, as a null mutant of UL12 displays a severe growth defect. Although the precise in vivo role of UL12 has not yet been determined, several in vitro activities have been identified for the protein, including endo- and exonuclease activities, interaction with the HSV-1 single-stranded DNA binding protein ICP8, and an ability to promote strand exchange in conjunction with ICP8. In this study, we examined a naturally occurring N-terminally truncated version of UL12 called UL12.5. Previous studies showing that UL12.5 exhibits nuclease activity but is unable to complement a UL12 null virus posed a dilemma and suggested that UL12.5 may lack a critical activity possessed by the full-length protein, UL12. We constructed a recombinant baculovirus capable of expressing UL12.5 and purified soluble UL12.5 from infected insect cells. The purified UL12.5 exhibited both endo- and exonuclease activities but was less active than UL12. Like UL12, UL12.5 could mediate strand exchange with ICP8 and could also be coimmunoprecipitated with ICP8. The primary difference between the two proteins was in their intracellular localization, with UL12 localizing to the nucleus and UL12.5 remaining in the cytoplasm. We mapped a nuclear localization signal to the N terminus of UL12, the domain absent from UL12.5. In addition, when UL12.5 was overexpressed so that some of the enzyme leaked into the nucleus, it was able to partially complement the UL12 null mutant.

The herpes simplex virus type 1 alkaline nuclease and single-stranded DNA binding protein mediate strand exchange in vitro

The replication of herpes simplex virus type 1 (HSV-1) DNA is associated with a high degree of homologous recombination. While cellular enzymes may take part in mediating this recombination, we present evidence for an HSV-1-encoded recombinase activity. HSV-1 alkaline nuclease, encoded by the UL12 gene, is a 5'-->3' exonuclease that shares homology with Redalpha, commonly known as lambda exonuclease, an exonuclease required for homologous recombination by bacteriophage lambda. The HSV-1 single-stranded DNA binding protein ICP8 is an essential protein for HSV DNA replication and possesses single-stranded DNA annealing activities like the Redbeta synaptase component of the phage lambda recombinase. Here we show that UL12 and ICP8 work together to effect strand exchange much like the Red system of lambda. Purified UL12 protein and ICP8 mediated the complete exchange between a 7.25-kb M13mp18 linear double-stranded DNA molecule and circular single-stranded M13 DNA, forming a gapped circle and a displaced strand as final products. The optimal conditions for strand exchange were 1 mM MgCl(2), 40 mM NaCl, and pH 7.5. Stoichiometric amounts of ICP8 were required, and strand exchange did not depend on the nature of the double-stranded end. Nuclease-defective UL12 could not support this reaction. These data suggest that diverse DNA viruses appear to utilize an evolutionarily conserved recombination mechanism.

Pseudorabies virus DNA-binding protein stimulates the exonuclease activity and regulates the processivity of pseudorabies virus DNase

The pseudorabies virus (PRV) DNase is an alkaline exonuclease and endonuclease, which exhibits an Escherichia coli RecBCD-like catalytic function. The PRV DNA-binding protein (DBP) promotes the renaturation of complementary single strands of DNA, which is an essential function for recombinase. To investigate the functional and physical interactions between PRV DBP and DNase, these proteins were purified to homogeneity. PRV DBP stimulated the DNase activity, especially the exonuclease activity, in a dose-dependent fashion. Acetylation of DBP by acetic anhydride resulted in a loss of DNA-binding ability and a 60% inhibition of the DNase activity, suggesting that DNA-binding ability of PRV DBP was required for stimulating the DNase activity. PRV DNase behaved in a processive mode; however, it was converted into a distributive mode in the presence of DBP, implying that PRV DBP stimulated the dissociation of DNase from DNA substrates. The physical interaction between DBP and DNase was further analyzed by enzyme-linked immunosorbent assay, and a significant interaction was observed. Thus, these results suggested that PRV DBP interacted with PRV DNase and regulated the DNase activity in vitro.

A colorimetric assay for high-throughput screening of inhibitors of herpes simplex virus type 1 alkaline nuclease

Herpes simplex virus type 1 (HSV-1) encodes a deoxyribonuclease that is frequently referred to as alkaline nuclease (AN) because of its elevated pH optimum. Studies with recombinant viruses which contain deletions in the HSV-1 gene encoding AN have indicated that this enzyme is required for efficient virus replication and therefore represents a potential target for novel antiviral therapies. A simple colorimetric assay for deoxyribonuclease activity employing a DNA-methyl green substrate was adapted for use in a high-throughput screen to identify small molecule inhibitors of this enzyme. This screen identified 1,2-benzoisothiazolin-3-one as a specific inhibitor of AN, since it exhibited activity against AN but was completely inactive against bovine pancreatic DNaseI. Subsequent studies revealed that this compound most likely inhibited AN by forming disulfide linkages with one or more exposed cysteine residues on the surface of the enzyme and that AN was sensitive to sulfhydryl-group-modifying reagents in general. These results demonstrated the utility of this DNA-methyl green substrate-based assay in both the rapid identification and the characterization of novel small molecule inhibitors of the AN encoded by HSV-1 and other herpesviruses.

Herpesvirus alkaline deoxyribonuclease; a possible candidate as a novel target for anti-herpesvirus therapy

Herpesvirus alkaline deoxyribonucrease (DNase) is coded in the genome of all herpesvirus species determined total sequence and is conserved in structure. In order to determine whether the enzyme could be a target for a novel antiherpesvirus therapy, the anti-herpes simplex virus type 1 (HSV-1) activity of antisense oligonucleotide for HSV-1 alkaline DNase was studied. Six antisense phosphorothioate oligonucleotides, targeted to an internal AUG start codon, were designed and evaluated. One of the oligonucleotides, UL12-4, inhibited wild type and thymidine kinase-deficient HSV-1 replication to 21.5 and 19.5% at 40 microM, respectively. The quantity of alkaline DNase mRNA and DNase activity in HSV-1-infected Vero cells was reduced to one eighth and 66.9% of control, respectively, by treatment with 40 microM of UL12-4, but no effect was observed on the quantity of HSV-1 glycoprotein H mRNA (gamma2 gene) or on the replication of Vero cells. These results indicate that UL12-4 inhibits HSV-1 replication by decreasing the amount of alkaline DNase mRNA. The herpesvirus alkaline DNase could be a novel target for anti-herpesvirus drug.

In vitro processing of herpes simplex virus type 1 DNA replication intermediates by the viral alkaline nuclease, UL12

Herpes simplex virus type 1 (HSV-1) DNA replication intermediates exist in a complex nonlinear structure that does not migrate into a pulsed-field gel. Genetic evidence suggests that the product of the UL12 gene, termed alkaline nuclease, plays a role in processing replication intermediates (R. Martinez, R. T. Sarisky, P. C. Weber, and S. K. Weller, J. Virol. 70:2075-2085, 1996). In this study we have tested the hypothesis that alkaline nuclease acts as a structure-specific resolvase. Cruciform structures generated with oligonucleotides were treated with purified alkaline nuclease; however, instead of being resolved into linear duplexes as would be expected of a resolvase activity, the artificial cruciforms were degraded. DNA replication intermediates were isolated from the well of a pulsed-field gel ("well DNA") and treated with purified HSV-1 alkaline nuclease. Although alkaline nuclease can degrade virion DNA to completion, digestion of well DNA results in a smaller-than-unit-length product that migrates as a heterogeneous smear; this product is resistant to further digestion by alkaline nuclease. The smaller-than-unit-length products are representative of the entire HSV genome, indicating that alkaline nuclease is not inhibited at specific sequences. To further probe the structure of replicating DNA, well DNA was treated with various known nucleases; our results indicate that replicating DNA apparently contains no accessible double-stranded ends but does contain nicks and gaps. Our data suggest that UL12 functions at nicks and gaps in replicating DNA to correctly repair or process the replicating genome into a form suitable for encapsidation.

Functional conservations of the alkaline nuclease of herpes simplex type 1 and human cytomegalovirus

The herpes simplex virus type 1 UL12 gene product, alkaline nuclease (AN), appears to be involved in viral DNA processing and capsid egress from the nucleus (Shao, L., Rapp, L. M., and Weller, S. K., Virology 196, 146-162, 1993). Although the HSV-1 AN is not absolutely essential for viral replication in tissue culture, conservation of the AN gene in all herpesviruses suggests an important role in the life cycle of herpesviruses. The counterpart of HSV-1 AN for human cytomegalovirus (HCMV) is the UL98 gene product. To examine whether the HCMV AN could substitute for HSV-1 AN, we performed trans-complementation experiments using a HSV-1 amplicon plasmid carrying the HCMV UL98 gene. Our results indicate (i) HCMV AN can complement the growth of the HSV-1 AN deletion mutant UL12lacZ virus in trans; (ii) a new recombinant virus, UL12laZcUL98/99, appears to be generated by the integration of the HCMV UL98 gene into the HSV-1 UL12lacZ viral genome; (iii) in contrast to its parental HSV-1 UL12lacZ virus, capsids formed in UL12lacZUL98/99-infected Vero cells were able to transport from the nucleus to the cytoplasm and mature into infectious viruses. Our results demonstrate a functional conservation of AN between HSV-1 and HCMV.

The exonuclease activity of HSV-1 UL12 is required for in vivo function

The herpes simplex virus type 1 (HSV-1) UL12 gene encodes an alkaline pH-dependent deoxyribonuclease termed alkaline nuclease. A recombinant UL12 knockout mutant, AN-1, is severely compromised for growth, and analysis of this mutant suggests that UL12 plays a role in processing complex DNA replication intermediates (R. Martinez, R. T. Sarisky, P. C. Weber, and S. K. Weller, (1996) J. Virol. 70, 2075-2085). This processing step may be required for the generation of capsids that are competent for egress from the nucleus to the cytoplasm. In this report, we address the question of whether the AN-1 growth phenotype is due to the loss of UL12 catalytic activity. We constructed two point mutations in a highly conserved region (motif II) of UL12 and purified wild-type and mutant enzymes from a baculovirus expression system. Both mutant proteins are stable, soluble, and competent for correct nuclear localization, suggesting that they have retained an intact global conformation. Neither mutant protein, however, exhibits exonuclease activity. In order to examine the in vivo effects of these mutations, we determined whether expression of mutant proteins from amplicon plasmids could complement AN-1. While the wild-type plasmid complements the growth of the null mutant, neither UL12 mutant can do so. Loss of exonuclease activity therefore correlates with loss of in vivo function.

Structure-function analysis of the herpes simplex virus type 1 UL12 gene: correlation of deoxyribonuclease activity in vitro with replication function

Although the product of the UL12 gene of herpes simplex virus type 1 (HSV-1) has been shown to possess both exonuclease and endonuclease activities in vitro, and deletion of most of the gene within the viral genome results in inefficient production and maturation of infectious virions, the function of the deoxyribonuclease (DNase) activity per se in virus replication remains unclear. In order to correlate the in vitro and in vivo activities of the protein encoded by UL12, mutant proteins were tested for nuclease activity in vitro by a novel hypersensitivity cleavage assay and for their ability to complement the replication of a DNase null mutant, AN-1. Rabbit reticulocyte lysates programmed with wild-type UL12 RNA cleaved at the same sites cleaved by purified HSV-1 DNase, but distinct from those cleaved by DNase 1 or micrococcal nuclease. All mutants which lacked DNase activity in vitro also failed to complement the replication of AN-1 in nonpermissive cells. Likewise, all mutants which contained HSV-1 DNase activity, as detected by the hypersensitivity cleavage assay, were capable of complementing the replication of the DNase null mutant, though to varying extents. Of particular note was the d1-126 mutant protein, which, despite having the same specific activity as the wild-type enzyme in vitro, complemented the replication of AN-1 significantly less than the wild-type protein. The results suggest that DNase activity per se is required for efficient replication of HSV-1 in vivo. However, residues, including the N-terminal 126 amino acids, which are dispensable for enzymatic activity in vitro may facilitate the accessibility or activity of the protein in vivo.

Structure-activity relationships and conformational features of antiherpetic pyrimidine and purine nucleoside analogues. A review

A rational approach to the design of antiherpetic nucleoside analogues is based in part on the broad specificity of virus-coded thymidine kinases. Herpes virus thymidine kinase 'activates' many 5-substituted 2'-deoxyuridines, analogues of thymidine (e.g., idoxuridine, trifluridine, edoxudine, brivudine), 5-substituted arabinofuranosyluracil derivatives (e.g., 5-Et-Ara-U, BV-Ara-U, Cl-Ara-U), acyclonucleosides of guanine (e.g., aciclovir, ganciclovir, penciclovir), and purine nucleosides with the pentafuranosyl ring replaced by a cyclobutane ring (e.g., cyclobut-G, cyclobut-A). Activation involves selective, and frequently regiospecific, phosphorylation of these analogues to the 5'-monophosphates. These are further phosphorylated by cellular enzymes to the 5'-triphosphates, which are usually competitive inhibitors of the viral-coded DNA polymerases. Some analogues are also incorporated into viral, and to a lesser extent cellular, DNA. A recent, unusual, exception is human cytomegalovirus, which does not code for a thymidine kinase, but for a protein with the sequence characteristics of protein kinase and which phosphorylates ganciclovir to its 5'-monophosphate. The interaction of the analogues with cellular catabolic enzymes such as uridine and thymidine nucleoside phosphorylases is also discussed, as is the relationship between physicochemical properties (configuration, conformation, electronic and hydrophobic parameters) and antiviral activities, with particular reference to those drugs that are licensed, or under consideration, for clinical use.

Early induction of DNA single-stranded breaks in cells infected by herpes simplex virus type 1

In cells infected with herpesviruses a series of host-cell nuclear changes can be observed in a temporal sequence, such changes include chromosome aberrations. The precise mechanism by which virus infection produces chromosome damage is not known. Previous studies have revealed modifications in the properties of chromatin from infected cells, but such modifications are not due to extensive breakdown of host DNA or alteration of the nucleosomal structure in bulk host chromatin. We have adapted and modified a fluorescence enhancement assay for DNA damage in order to study the effects of herpes simplex virus type 1 infection on the integrity of the host-cell DNA. Here it is reported that HSV-1 induces a significant number of single-stranded breaks in the host-cell DNA at early hours post-infection. Such breaks seem not to be directly related to the major breakdown of host-cell DNA seen at later times post-infection.

Inhibition of herpes simplex virus types 1 and 2 replication in vitro by mercurithio analogs of deoxyuridine

The in vitro antiviral activity of several 5-mercurithio analogs of 2'-deoxyuridine (dUrd) on the replication of herpes simplex virus types 1 (HSV-1) and 2 (HSV-2) were examined. Of those compounds tested, the thioglycerol analog of 5-mercuri-2'-deoxyuridine (HgdUrd) was most effective in inhibiting the replication of HSV-1 in KB cells with a 50% inhibitory dose (ID50) of 0.001 micrograms/ml while the glutathione analog of HgdUrd was the most effective in inhibiting the replication of HSV-2 with a ID50 of 0.075 micrograms/ml. Conversely in HeLa TK- cells, the mercaptoguanosine analog of HgdUrd was the most effective compound in inhibiting virus replication with ID50S of 0.098 and 0.001 micrograms/ml for HSV-1 and HSV-2 respectively. These results suggest that these mercurithio analogs of dUrd are as effective as acyclovir in preventing the replication of these herpesviruses.

Comparison of exonucleolytic activities of herpes simplex virus type-1 DNA polymerase and DNase

The exonucleolytic activities associated with herpes simplex virus type-1 (HSV-1) DNA polymerase and DNase were compared. The unique properties of these nucleases were assessed by applying biochemical and immunological methods as well as by genetics. In contrast to the viral DNA polymerase, HSV DNase is equipped with a 5'-3'-exonuclease activity. Under reaction conditions optimal for HSV DNA polymerase, i.e. at high ionic strength, HSV DNase exhibited only limited endonucleolytic activity and degraded double-stranded DNA in a very processive manner and exclusively in the 5'-3' direction, producing predominantly mononucleotides. Both viral enzymes displayed significant RNase activity which could be correlated with the endogenous endonucleolytic and 5'-3'-exonucleolytic activities of the DNase and the polymerase-associated 3'-5' exonuclease. The tight linkage of polymerizing and exonucleolytic functions of the viral DNA polymerase was demonstrated by their identical response to (a) thermal inactivation, (b) drug inhibition and (c) neutralization by polyclonal antibodies reacting specifically with the N-terminal, central and C-terminal polypeptide domains of HSV-1 DNA polymerase. From the data presented it can be concluded that the cryptic 3'-5' exonuclease is the only exonucleolytic activity associated with the viral DNA polymerase.

Demonstration of the human herpesvirus 6-induced DNA polymerase and DNase

Infection of HSB-2 cells with human herpesvirus 6 (HHV6) results in an approximately 51-fold increase in the level of DNA polymerase activity and a 4.44-fold increase in the level of DNase activity when compared to mock-infected cells. There was no increase in thymidine kinase, uracil-DNA glycosylase, or deoxyuridine triphosphate nucleotidohydrolase activities in the infected cells. The HHV6-induced DNase and DNA polymerase activities could be distinguished from their normal cellular counterparts on the basis of immunological specificities and in the case of DNA polymerase based upon differences in electrophoretic migration. Serological studies also demonstrated reactivity of the antisera not only for HHV6 but also for Epstein-Barr virus.

Identification and some properties of a unique DNA polymerase from cells infected with human B-lymphotropic virus

A new DNA polymerase and DNase activity were identified from cells infected with human B-lymphotropic herpesvirus (HBLV). DNA polymerase associated with HBLV infection was similar in its sensitivity to inhibition by ppi analogs as other herpesvirus-specific DNA polymerases but was dissimilar in its inhibition by certain nucleoside triphosphates.

The role of viral and cellular nuclear proteins in herpes simplex virus replication

Following infection of cells by herpes simplex virus, the cell nucleus is subverted for transcription and replication of the viral genome and assembly of progeny nucleocapsids. The transition from host to viral transcription involves viral proteins that influence the ability of the cellular RNA polymerase II to transcribe a series of viral genes. The regulation of RNA polymerase II activity by viral gene products seems to occur by several different mechanisms: (1) viral proteins complex with cellular proteins and alter their transcription-promoting activity (e.g., alpha TIF), (2) viral proteins bind to specific DNA sequences and alter transcription (e.g., ICP4), and (3) viral proteins affect the posttranslational modification of viral or cellular transcriptional regulatory proteins (e.g., possibly ICP27). Thus, HSV may utilize several different approaches to influence the ability of host-cell RNA polymerase II to transcribe viral genes. Although it is known that viral transcription uses the host-cell polymerase II, it is not known whether viral infection causes a change in the structural elements of the nucleus that promote transcription. In contrast, HSV encodes a new DNA polymerase and accessory proteins that complex with and reorganize cellular proteins to form new structures where viral DNA replication takes place. HSV may encode a large number of DNA replication proteins, including a new polymerase, because it replicates in resting cells where these cellular gene products would never be expressed. However, it imitates the host cell in that it localizes viral DNA replication proteins to discrete compartments of the nucleus where viral DNA synthesis takes place. Furthermore, there is evidence that at least one specific viral gene protein can play a role in organizing the assembly of the DNA replication structures. Further work in this system may determine whether assembly of these structures is essential for efficient viral DNA replication and if so, why assembly of these structures is necessary. Thus, the study of the localization and assembly of HSV DNA replication proteins provides a system to examine the mechanisms involved in morphogenesis of the cell nucleus. Therefore, several critical principles are apparent from these discussions of the metabolism of HSV transcription and DNA replication. First, there are many ways in which the activity of RNA polymerase II can be regulated, and HSV proteins exploit several of these in controlling the transcription of a single DNA molecule. Second, the interplay of these multiple regulatory pathways is likely to control the progress of the lytic cycle and may play a role in determining the lytic versus latent infection decision.(ABSTRACT TRUNCATED AT 400 WORDS)

Alkaline nuclease activity in cells infected with herpes simplex virus type 1 (HSV-1) and HSV-1 temperature-sensitive mutants

An in situ assay has been adapted to the herpes simplex virus type 1 (HSV-1) system which can detect alkaline nuclease activity in infected cell lysates following sodium dodecylsulfate polyacrylamide gel electrophoresis. Lysates of cells infected with HSV-1 temperature-sensitive (ts) mutants possessing mutations in the genes for an immediate-early transcriptional regulatory protein (ICP4), viral DNA polymerase (pol), and the major HSV-1 DNA binding protein (ICP8) exhibited altered alkaline nuclease profiles relative to that of wild-type virus-infected cells at 39 degrees C. Infections with a control mutant defective in the gene for glycoprotein B yielded wild-type nuclease profiles. The diverse effects on alkaline nuclease expression of mutants with lesions in different viral proteins involved directly in viral DNA synthesis provides evidence for the cooperative interaction between HSV-encoded viral DNA replication components.

In situ detection of alkaline nuclease activity in cells infected with herpes simplex virus type 1 (HSV-1)

An in situ assay for detection of alkaline nuclease activities has been adapted to the herpes simplex virus type 1 (HSV-1) system. Six major nuclease activities which migrate with molecular weights of 90,000, 85,000, 80,000, 76,000, 71,000 and 65,000, and six minor species of molecular weights 87,000, 81,000, 57,000, 18,500, 17,500 and 16,500 were detected in lysates of HSV-1 infected cells following SDS-polyacrylamide gel electrophoresis and enzyme activation in situ. An ELISA assay and an immunoprecipitation study indicated that the six major HSV-induced nuclease species are virus-specific. Moreover, a reconstruction experiment in which 14C-labelled protein markers were incubated with mock- and HSV-infected cell lysates demonstrates that the nuclease fractions detected in situ were not due to endogenous proteolytic activity. The 80,000, 76,000, 71,000 and 65,000 species were first detected at 4 h post-infection, whereas all others were detectable by 6 h post-infection. The activities of the major cellular nucleases of molecular weights 50,000. 48,000 and 45,000 decreased as a function of time post-infection. The level of expression of each of the virus-induced species was dependent upon the multiplicity of infection, and all virus-induced activities exhibited biochemical properties characteristic of purified HSV-1 alkaline nuclease, including activation and inhibition by specifications. The 76,000 HSV-induced alkaline nuclease species was also demonstrated to possess endonucleolytic activity.

An optimized thymidylate kinase assay, based on enzymatically synthesized 5-[125I]iododeoxyuridine monophosphate and its application to an immunological study of herpes simplex virus thymidine-thymidylate kinases

The biological synthesis and purification of 5-[125I]iododeoxyuridine monophosphate (IdUMP) are described. The specificity of IdUMP as substrate in the thymidylate monophosphate kinase (TMPK) assay is demonstrated, and a 100-fold gain in sensitivity as compared to the conventional TMPK assay is shown. TMPK measurements of isozymes derived from herpes simplex virus (HSV)-infected cells, uninfected cells, and tumor biopsies were performed. The results showed a significant difference in dependence of phosphate donor concentration present for TMPK activity from HSV-infected cells compared to the corresponding activity from uninfected cells, while only a minor difference in pH optima was observed for these enzyme activities. The increased sensitivity made it possible to detect and quantify HSV TMPK-blocking antibodies (ab) present in human sera. Sera from HSV ab-positive individuals were found to block the two HSV TMPKs to varying degrees and with different specificities. The immunological relationship between the TMPK and thymidine kinase (TK) induced by HSV-1 and HSV-2, respectively, was studied by comparing the capacities of different sera to block the two enzymatic activities. The results showed that the capacity to block HSV-1 TK and TMPK was proportional for all of the sera studied, while sera that preferentially blocked only the HSV-2 TMPK or HSV-2 TK were found. It was concluded that the HSV-2 TMPK and TK activities are less related than the corresponding activities for HSV-1 and that the HSV-2 enzyme activities are mediated by different catalytic sites.

Characterization of a herpes simplex virus type 2 deoxyuridine triphosphate nucleotidohydrolase and mapping of a gene conferring type specificity for the enzyme

The herpes simplex virus type 2 (HSV-2)-induced deoxyuridine triphosphate nucleotidohydrolase (dUTPase) was purified approximately 600 +/- 43-fold using a combination of affinity, hydrophobic, absorption, and ion-exchange chromatography techniques. The only substrate for the dUTPase was dUTP with a Km of 3.6 +/- 1.1 microM. There was no apparent divalent cation requirement, but the HSV-2-induced dUTPase was inhibited by EDTA (0.1 mM) and this inhibition was reversed by either Co2+ (0.5 mM) or Mg2+ (0.5 mM). The HSV-2-induced dUTPase was distinguished from the HSV-1-induced and cellular dUTPases based upon differences in sensitivity to substrate inhibition, thermostability, and electrophoretic migration in nondenaturing polyacrylamide gels. Analysis of HSV-1 temperature-sensitive (ts) mutants demonstrated that ts A15 and ts K13 did not induce significant amounts of dUTPase activity at the permissive or nonpermissive temperatures. Mutants with defects in HSV-induced DNA polymerase or in the major DNA binding protein induced dUTPase at both temperatures. In contrast ts mutants defective in the alpha polypeptide VP175 (ICP4) did not induce normal levels of dUTPase at the nonpermissive temperature. The location of a gene encoding for the type specificity of the HSV induced dUTPase was mapped to the left 20% of the genome in Us in the region 0.060 to 0.100 or from 0.148 to 0.204.

Nucleotide sequence of the DNA polymerase gene of herpes simplex virus type 2 and comparison with the type 1 counterpart

The complete nucleotide sequence of the DNA polymerase gene of herpes simplex virus (HSV) type 2 strain 186 has been determined. The gene included a 3720-bp major open reading frame capable of encoding 1240 amino acids. The predicted primary translation product had an Mr of 137,354, which was slightly larger than its HSV-1 counterpart. A comparison of the predicted functional amino acid sequences of the HSV-1 and HSV-2 DNA polymerases revealed 95.5% overall amino acid homology, the value of which was the highest among those of the other known polypeptides encoded by HSV-1 and HSV-2. The functional amino acid changes were spread in the N-terminal one-third of the protein, whereas the C-terminal two-third was almost identical between the two types except a particular hydrophilic region. A highly conserved sequence of 6 aa, YGDTDS, which has been observed in DNA polymerases of HSV-1, Epstein-Barr virus, adenovirus, and vaccinia virus, was also present at positions 889 to 894 in the C-terminal region of HSV-2 DNA polymerase.

Temperature-sensitive herpes simplex virus type 1 mutants defective in the shutoff of cellular DNA synthesis and host polypeptide synthesis

Two temperature-sensitive herpes simplex virus type 1 mutants, ts 1-8 and ts 199, belonging to different complementation groups, were isolated. Both mutants were defective in the shutoff of host DNA synthesis at 39.5 degrees C (nonpermissive temperature). ts 1-8 exhibited intermediate levels of viral DNA synthesis at 39.5 degrees C, while ts 199 was completely deficient in viral DNA synthesis at 39.5 degrees C. Comparative polyacrylamide gel electrophoresis of the ts 1-8, ts 199 and wild-type viral-coded polypeptides and cellular proteins produced in vivo at 34 degrees C and 39.5 degrees C during various periods post infection was performed. The results indicated that ts 1-8 and ts 199 were temperature-sensitive for the secondary suppression of host polypeptide synthesis. Production of the beta (early) and gamma (late) viral polypeptides was slightly delayed in the mutant-infected cells at early times post infection at both 34 degrees C and 39.5 degrees C. This delayed protein production was not evident at later times post-infection. The ts 1-8 and ts 199 mutants were distinct from the HSV-1 viron-associated host shutoff (vhs) mutants of Read and Frenkel (J. Virol. 46 (1983) 498).

Herpes simplex virus gene products involved in the induction of chromosomal aberrations

The effect of short-term herpes simplex virus type 1 (HSV-1) infection on chromosomes of human diploid fibroblasts was examined. In addition to chromosomal breaks, gaps and pulverization, three kinds of cytogenetic damage (double minutes, polyploidy and endoreduplication) not yet reported following productive infection with HSV or other animal viruses were frequently observed. Consistent with previous studies suggesting that the expression of immediate-early and/or early viral gene products is required for the induction of chromosomal damage, was the observation that cells infected at the nonpermissive temperature with HSV-1 temperature-sensitive mutants defective in the gene for the immediate-early transcriptional regulatory protein, ICP4, and three early viral gene products--DNA polymerase (pol), the major HSV DNA-binding protein (ICP8) and an HSV-2 mutant defective in alkaline nuclease--exhibited altered patterns of chromosomal damage relative to the effects of wild-type virus on infected cells. These findings suggest a direct or indirect role for all four gene products in the induction of chromosomal damage. In cells infected with wild-type virus for 4 h or longer, HSV proved to be a more potent mitotic arresting agent than colcemid. Moreover, studies with selected mutants indicate that HSV pol specifically may be involved in mitotic arrest. Additionally, in cells infected at the non-permissive temperature with a pol mutant, the number of polyploid metaphases was reduced 4-fold relative to that seen in wild-type virus-infected cells suggesting a role for HSV pol in the amplification of cellular DNA.

Mothers of children with Down syndrome have higher herpes simplex virus type 2 (HSV-2) antibody levels

The antibody response to herpes simplex virus (HSV) was studied in 53 mothers of children with Down syndrome (Ds) and compared with that in 154 controls, using sera sampled during pregnancy or at delivery. Conventional analysis of HSV complement fixing antibodies showed the same frequency of positivity for the two groups (70%). When the levels of IgG antibodies to an HSV-1 and an HSV-2 antigen preparation were determined by an enzyme-linked immunosorbent assay (ELISA) technique, it was found that the Ds and control mothers had similar levels of IgG antibodies to HSV-1, whereas the level of IgG antibodies to HSV-2 was significantly (P less than 0.001) higher in Ds mothers. The ratio of HSV-2 to HSV-1 ELISA IgG was calculated for each mother and the distribution of these ratios also differed significantly between the control and Ds mothers. The differences found were not due to differences in age distribution in the control and Ds groups. For comparison a third procedure, measurement of thymidine kinase blocking antibody (TK ab), was used. With this procedure the mothers were divided into groups estimated to be positive for HSV-1, HSV-2, or both. Statistical analyses showed a good correlation between the type found in TK ab analyses and the ratio found in the ELISA HSV test. The results clearly demonstrated an overrepresentation of HSV-2 antibody positivity among Ds mothers, though not of sufficient magnitude to imply that HSV-2 can be the major cause of Ds. It is discussed whether HSV-2 might be related to the recently increased birthrate of children with Ds among young mothers in Sweden or to localized geographical clustering of Ds births, or whether the increased HSV-2 antibody positivity merely indicates that factors following the same epidemiological pattern are involved in the aetiology of Ds.

Epstein-Barr virus induces a unique pyrimidine deoxynucleoside kinase activity in superinfected and virus-producer B cell lines

Epstein-Barr (EB) virus induces a new pyrimidine deoxynucleoside kinase [thymidine kinase (dTk)] activity in Raji B lymphocyte cells after superinfection. This dTk activity is also present in small amounts in the HR-1 virus-producer cell line and in larger amounts in the B95-8 virus-producer line. The dTk activity induced by EB virus coelutes from DEAE-cellulose columns with deoxycytidine kinase (dCk) activity and elutes as a broad peak well separated from the large peaks of cellular dTk and dCk activities. This EB virus-induced pyrimidine deoxynucleoside kinase activity from HR-1 cells differs from cellular kinases in most basic biochemical properties but shares certain properties with the herpes simplex virus dTk.

Physical mapping of the herpes simplex virus type 2 nuc- lesion affecting alkaline exonuclease activity by using herpes simplex virus type 1 deletion clones

The nuc- lesion affecting alkaline exonuclease activity in the herpes simplex virus type 2 (HSV-2) mutant ts1348 had previously been mapped to the EcoRI-D restriction enzyme fragment of HSV-1. Eight clones with deletions representing most of HSV-1 EcoRI fragment D were selected with lambda gtWES hybrids. These clones were tested for their ability to rescue the alkaline exonuclease activity of HSV-2 nuc- ts1348 virus. The sequences colinear with the HSV-2 nuc- lesion were found to map between 0.169 and 0.174 map units on the HSV-1 Patton genome, representing an 0.8-kilobase-pair region that is 12.9 to 13.7 kilobase pairs from the left end of HSV-1 EcoRI fragment D.

DNA polymerase in nuclei isolated from herpes simplex virus type-2-infected cells. Characterization of the reaction product and inhibition by substrate analogs

Nuclei isolated from herpes simplex virus (HSV) type 2-infected KB cells were examined for their capacity to serve as an in situ source of herpes DNA polymerase. In contrast to purified enzymes with added template, approx. 80% of the DNA synthesized in isolated nuclei was viral. The average size of DNA fragments labeled in vitro was 3.2 X 10(6) Da. Based on an increase in DNA density when nuclei were incubated in the presence of BrdUTP rather than dTTP, 16% of the nucleotides were added during the in vitro reaction. Sucrose gradient analysis of DNA polymerase activity in extracts of isolated nuclei demonstrated the nearly exclusive presence of herpes DNA polymerase. Km concentrations for the four dNTPs were from 0.14 to 0.55 microM. DNA synthesis was inhibited competitively by the 5'-triphosphates of ara-A and ara-C (Ki = 0.03 and 0.22 microM, respectively) but not by the 5'-triphosphate of dideoxythymidine. aATP also served as a substrate (Km = 0.014 microM) for the reaction. We conclude that nuclei from HSV-infected cells have significant advantages for the detailed study of inhibitors of herpesvirus replication.

Epstein-Barr virus-specific DNase activity in nonproducer Raji cells after treatment with 12-o-tetradecanoylphorbol-13-acetate and sodium butyrate

An Epstein-Barr virus (EBV)-specific DNase was induced in EBV nonproducer Raji cells after treatment with 12-O-tetradecanoylphorbol-13-acetate and sodium butyrate. The increase in EBV DNase activity was related to the appearance of early antigen-positive cells. The enzyme had a sedimentation coefficient of 4S and was resistant to 300 mM KCl, and its induction did not depend on viral DNA synthesis. The EBV-specific DNase activity was specifically inhibited by sera from patients who had nasopharyngeal carcinoma with high early antigen activities but not by sera from normal, healthy individuals. There was a correlation between the degree of anti-EBV DNase activity and the titers of early antigen antibody.