Organization of the left-hand end of the herpes simplex virus type 2 BglII N fragment

The genome sequence of herpes simplex virus type 2

The genomic DNA sequence of herpes simplex virus type 2 (HSV-2) strain HG52 was determined as 154,746 bp with a G+C content of 70.4%. A total of 74 genes encoding distinct proteins was identified; three of these were each present in two copies, within major repeat elements of the genome. The HSV-2 gene set corresponds closely with that of HSV-1, and the HSV-2 sequence prompted several local revisions to the published HSV-1 sequence (D. J. McGeoch, M. A. Dalrymple, A. J. Davison, A. Dolan, M. C. Frame, D. McNab, L. J. Perry, J. E. Scott, and P. Taylor, J. Gen. Virol. 69:1531-1574, 1988). No compelling evidence for the existence of any additional protein-coding genes in HSV-2 was identified.

Nucleotide sequence of the major DNA-binding protein gene of herpes simplex virus type 2 and a comparison with the type 1

The nucleotide sequence of a region encompassing about 5,200 base pairs (bp) of the left side of the origin of replication in the long unique region of the herpes simplex virus type 2 (HSV-2) has been determined. This region contained the major DNA-binding protein or the infected-cell protein 8 (ICP 8) gene and 5'-part of the counterpart of HSV-1 ICP 18.5 gene. A comparison of the nucleotide sequence of the ICP8 gene between HSV-1 and HSV-2 showed an 89.8% homology. A primer extension analysis for the HSV-2 ICP 8 mRNA showed that the major transcriptional start site was mapped at 315 bp upstream of the initiation codon. A comparison of the predicted functional amino acid sequence of the ICP 8 between HSV-1 and HSV-2 revealed a striking homology (97.2%), the value of which was the highest among those of the other polypeptides encoded by HSV-1 and HSV-2. Some domains, which were shown to be required for the nuclear function, the binding to single-stranded DNA and the nuclear localization were well conserved. In addition, the nucleotide and the functional amino acid sequences of a part of the HSV-2 counterpart of the HSV-1 ICP 18.5 gene were also compared, demonstrating an 88.4% and 95.9% homology, respectively.

Sequencing and 5'- and 3'-end transcript mapping of the gene encoding the small subunit of ribonucleotide reductase from bovine herpesvirus type-1

The complete nucleotide sequence of the gene encoding the small subunit of ribonucleotide reductase (RNR) from bovine herpesvirus type-1 (BHV-1) was determined. The genomic DNA fragment sequenced also represented regions corresponding to the carboxy termini of RNR large subunit and of a virion protein causing host shut-off. The small subunit polypeptide was constituted of 314 amino acid residues totalling 35.25 kDa. The major transcription initiation and termination sites of the small subunit mRNA were located 95 bases upstream and 88 nucleotides downstream from the coding region, respectively. These findings indicate that the mRNA was 1128 bases long which correlated well with the size of the polyadenylated transcript detected in Northern blot analysis (1.3 kb). Within the RNR large subunit coding region, a TATA box and two CAAT box motifs were found 26, 104, and 190 nucleotides, respectively, upstream from the transcription initiation site of the small subunit mRNA. In contrast to previous studies (Slabaugh et al., J. Virol. 1988, 62, 519-527; Boursnell et al., Virology 1991, 184, 411-416), our comparative analysis of five herpesviruses, one iridovirus, and one poxvirus small subunit protein sequences suggested that the seven viruses arose from a common lineage.

Genomic sequences homologous to the protein kinase region of the bifunctional herpes simplex virus type 2 protein ICP10

The large subunit of herpes simplex virus type 2 (HSV-2) ribonucleotide reductase (ICP10) consists of two functional domains. The amino (N)-terminal domain at residues 1-411 has serine/threonine-specific kinase activity (PK domain) and is encoded by a DNA fragment with transforming potential (15,17). The remaining region is required for ribonucleotide reductase activity (RR domain) (14, 15). Computer-assisted comparison of the ICP10 sequence to the EMBL database 21 has revealed sequences within the RR domain that are common to all RR1 proteins. Motifs homologous to the catalytic domains of all PKs were identified in the PK region (15). However, based on this database all other sequences were unique. Secondary structure analysis of the PK and RR junction region of ICP10 identified twist angle variations with helical periodicity characteristic of enhancer elements. Sequences homologous to a segment of the PK domain were amplified and cloned from human DNA using the polymerase chain reaction (PCR), suggesting that the PK domain may have originated from a cellular gene.

Herpes simplex virus-encoded ribonucleotide reductase: evidence for the dissociation/reassociation of the holoenzyme

35S-labeled cells infected with herpes simplex virus type 1 (HSV-1), temperature-sensitive (ts) mutant ts 1222 were used as a source of the large subunit of the viral ribonucleotide reductase (RR) to investigate the binding of the large (RR1) and small (RR2) subunits in the active enzyme. Mixing 35S-labeled RR1 from ts 1222 with unlabeled RR1/RR2 complex from wild type (wt) infected cells resulted in the formation of a complex between 35S-labeled RR1 and unlabeled RR2, indicating that the complex between the RR1 and RR2 subunits is dynamic and subunit dissociation/reassociation occurs during enzyme function. Similar results were obtained when unlabeled HSV-2 RR was substituted for HSV-1 RR, demonstrating that the holoenzyme can be formed the large subunit of HSV-1 RR and the small subunit of HSV-2.

DNA sequence and RNA transcription through a site of recombination in a non-neurovirulent herpes simplex virus intertypic recombinant

RE6 is a herpes simplex type-1 (HSV-1) X herpes simplex type-2 (HSV-2) intertypic recombinant that cannot replicate in the adult mouse nervous system. In the accompanying report, we have shown that HSV-1 sequences between 0.698 and 0.721 map units can restore a partial neurovirulent phenotype to RE6. In this report, we have used comparative DNA sequence analysis of RE6, 17syn+ (HSV-1) and HG52 (HSV-2) to demonstrate that this region contains a site of recombination between HSV-1 and HSV-2 sequences in RE6. High resolution transcription analysis has demonstrated that three readily detected transcripts are present in this region of the genome. In addition, the 5' end of a low abundance 5 kb transcript was also located in the right-hand portion of this region. All the transcripts encoded by HSV-1 and HSV-2 in this region of the genome are expressed by the RE6 recombinant. This and our sequence data suggest that the lack of neurovirulence in RE6 is not due to a simple loss in the expression of a transcript or to a defect in a protein encoded by a gene at the site of recombination.

Sequence analyses of herpesviral enzymes suggest an ancient origin for human sexual behavior

Comparison of the amino acid sequences of the deoxythymidine kinases of herpes simplex (HSV) and of marmoset herpes viruses (MHV) suggests a divergence time of 8 to 10 million years ago for HSV-1 and -2. Like MHV, HSV-1 and -2 cause local infections in their natural hosts, and direct contact between two individuals during the brief period of infectivity is needed for transmission. Because B virus, a nearer relative of HSV, depends on both oral and genital routes of transmission, we postulate that ancestral HSV (aHSV) was similar, and that for HSV-1 and -2 to diverge, genital and oral sites had to become microbiologically somewhat isolated from each other, while oral--oral and genital--genital contact had to be facilitated to maintain both aHSV strains. We propose that acquisition of continual sexual attractiveness by the ancestral human female and the adoption of close face-to-face mating, two hallmarks of human sexual behavior, provided the conditions for the divergence.

Identification of viral polypeptides involved in pseudorabies virus ribonucleotide reductase activity

We studied pseudorabies virus-induced ribonucleotide reductase and found that it exhibited biochemical properties very similar to those of herpes simplex virus reductase. A polyclonal rabbit antiserum (P9) directed against the carboxy terminus of subunit H2 polypeptide (38,000 daltons) of herpes simplex virus reductase neutralized the pseudorabies virus reductase, as well as the herpes simplex virus isozyme. This serum recognized two pseudorabies virus-specified polypeptides of 34,000 and 110,000 daltons, which may represent the two subunits of the enzyme. Furthermore, as already shown for herpes simplex virus reductase (E. A. Cohen, P. Gaudreau, P. Brazeau, and Y. Langelier, Nature [London] 321:441-443, 1986), we show that the nonapeptide itself specifically inhibited pseudorabies reductase activity.

Neutralization of herpes simplex virus ribonucleotide reductase activity by an oligopeptide-induced antiserum directed against subunit H2

Herpes simplex virus type 1 ribonucleotide reductase is associated with two polypeptides of apparent molecular weights 136,000 and 38,000. The two polypeptides form a tight complex and, therefore, are often coprecipitated by monoclonal antibodies. We report here that immunoglobulins G purified from polyclonal rabbit antisera (P9) raised against a nonapeptide corresponding to the carboxy terminus of the 38,000-dalton polypeptide specifically neutralize the herpes simplex virus ribonucleotide reductase activity. We suggest that the P9 immunoglobulin G neutralizes the reductase activity by impairing the association of the two subunits (H1 and H2) of the enzyme.

Structural features of ribonucleotide reductase

Herpes simplex virus type 1 (HSV-1) encodes a ribonucleotide reductase which comprises two polypeptides with sizes of 136,000 (RR1) and 38,000 mol. wt. (RR2). We have determined the entire DNA sequence specifying HSV-1 RR1 and have identified two adjacent open reading frames in varicella-zoster virus (VZV) which have homology to HSV RR1 and RR2; the predicted sizes for the VZV RR1 and RR2 polypeptides are 87,000 and 35,000 mol. wt. respectively. Amino acid comparisons with RR1 and RR2 polypeptides from other organisms indicate that HSV-1 RR1 contains a unique N-terminal domain which is absent from other RR1 polypeptides apart from HSV-2 RR1. These N-terminal amino acid sequences are poorly conserved between HSV-1 and HSV-2 in contrast to the remainder of the protein which shows greater than 90% homology. Polypeptide structural predictions suggest that the HSV-1 N-terminal domain may be separated into two regions, namely, a beta-sheet structure followed by a nonstructured area. Across the remainder of RR1 and RR2, comparisons also reveal blocks of amino acids conserved between the different ribonucleotide reductases, and these may be important for enzyme activity. From predictions on the structure of these conserved blocks, we have proposed that the location of a substrate binding site within RR1 is centered on three conserved glycine residues in a region which is predicted to adopt a beta-sheet/turn/alpha-helical structure; this approximates to the structure for ADP nucleotide binding folds. Finally, we propose that the promoters for the HSV and Epstein-Barr virus (EBV) RR2 transcripts have evolved by separate evolutionary routes.

Specific inhibition of herpesvirus ribonucleotide reductase by a nonapeptide derived from the carboxy terminus of subunit 2

Ribonucleotide reductase, an essential enzyme for the synthesis of deoxyribonucleotides, is formed by the association of two nonidentical subunits in almost all prokaryotic and eukaryotic cells. The same model probably holds for the herpes simplex virus (HSV)-encoded ribonucleotide reductase; two polypeptides of relative molecular mass 136,000 (136K; H1) and 40K (H2) (referred to elsewhere as RR1 and RR2; see for example, Dutia et al.) have been associated with the viral enzyme by both genetic and immunological studies. Furthermore, DNA sequence analyses have shown significant stretches of amino-acid homology between these viral polypeptides and those of, respectively, subunit 1 (ref. 12) and subunit 2 (ref. 13) of the Escherichia coli and mammalian enzymes. To assess the involvement of the 40K polypeptide in reductase activity, we synthesized a nonapeptide corresponding to the sequence of its carboxy terminus with the intention of raising neutralizing antibodies specific for the viral activity (E.A.C. et al., in preparation). We report here the unexpected finding that the nonapeptide itself specifically inhibits the HSV ribonucleotide reductase activity in a reversible, non-competitive manner, and we suggest that it does this by impairment of the correct association of the two subunits. This phenomenon emphasizes the potential usefulness of synthetic peptides in probing critical sites involved in macromolecular interactions.

Herpes simplex virus specifies two subunits of ribonucleotide reductase encoded by 3'-coterminal transcripts

We have previously described a transcription unit located between map coordinates 0.558 and 0.595 on the herpes simplex virus type 2 strain 333 genome which encodes two mRNAs of 5.0 and 1.2 kilobases that share a common 3' terminus, and we have determined the nucleotide sequence of a 38,000-dalton protein specified by the smaller RNA (D. A. Galloway and M. A. Swain, J. Virol. 49:724-730, 1984). The entire nucleotide sequence of the 140,000-dalton protein specified by a 3,432-base-pair open reading frame within the large mRNA is presented, as are transcriptional regulatory sequences upstream of the RNA. The 140,000-dalton protein shows strong homology with the large subunit of well-characterized ribonucleotide reductase enzymes from the mouse and from Escherichia coli and with an Epstein-Barr virus gene. The 38,000-dalton protein has been shown previously to have homology with the small subunit of these enzymes (B.-M. Sjoberg, H. Eklund, J. A. Fuchs, J. Carlson, N. M. Standart, J. V. Ruderman, S. J. Bray, and T. Hunt, FEBS Lett. 183:99-102, 1985). This is the first example of a herpesvirus transcriptional unit that encodes functionally related proteins.

HSV infected RAJI-cells specify HSV specific immediate early and/or early DNA-binding proteins

Herpes Simplex Virus specified DNA-binding proteins were purified from virus infected VERO and RAJI cells. The expression of the proteins differed depending on the type of the host cell. Polypeptides corresponding to HSV-1 specific ICP 8 and HSV-2 specific ICSP 11/12 were the major products of HSV-infected VERO cells. In RAJI cells polypeptides with a corresponding molecular weight, together with a cellular protein having almost similar mobility on SDS gels could be detected. Using immuno-blotting technique the HSV origin of these 135K molecular weight proteins synthesized in the HSV-1 and HSV-2-infected RAJI cells could be confirmed.

Characterization of the genes encoding herpes simplex virus type 1 and type 2 alkaline exonucleases and overlapping proteins

A detailed sequence analysis of the herpes simplex virus type 1 (HSV-1) and HSV-2 DNA encoding the alkaline exonuclease mRNA clusters has been completed. Three partially colinear mRNAs (2.3, 1.9, and 0.9 kilobases) are completely encoded within the DNA sequence presented. The putative promoter regions of the transcripts were inserted upstream of a plasmid-borne chloramphenicol acetyl transferase (CAT) gene and assayed for their ability to induce transcription of the CAT gene upon low multiplicity of infection with HSV in transient expression assays. We conclude that the expression of all three transcripts appear to be controlled by individual promoters. The 2.3-kilobase mRNA contains an open translational reading frame sufficient to encode 626 amino acids for the HSV-1 alkaline exonuclease enzyme; this value is 620 amino acids for HSV-2. A comparison of the predicted amino acid sequences of the HSV-1 and HSV-2 alkaline exonuclease enzymes revealed significant amino acid differences in the N-terminal portions of the two proteins; however, computer analyses suggest that the three-dimensional structures of the HSV-1 and HSV-2 nuclease enzymes are very similar. The 0.9-kilobase mRNA contains an open reading frame which shares a small amount of out-of-phase overlap with the C-terminal portion of the alkaline nuclease open reading frame. This open reading frame has the capacity to encode a 96-amino-acid polypeptide (10,500 daltons).

Multistep transformation by defined fragments of herpes simplex virus type 2 DNA: oncogenic region and its gene product

Diploid Syrian hamster embryo cells transfected with Bgl II C fragment of herpes simplex virus type 2 DNA acquired a neoplastic phenotype. Cultures transfected with its left-hand 64% subclone EcoRI/HindIII fragment AE (0.419-0.525 map unit) grew into established but nontumorigenic lines. Transfection of EcoRI/HindIII AE-immortalized cells with a 4.4-kilobase Sac I/BamHI subfragment within BamHI E (0.554-0.584 map unit; overlaps the right-hand 16% of Bgl II C) converted them to tumorigenicity. The 4.4-kilobase subfragment encodes a 144-kDa protein immunologically and structurally similar to an infected cell protein designated ICP 10. DNA extracted from cells transformed with the 4.4-kilobase subfragment exhibited discrete hybridizing bands homologous to BamHI E fragment. Monoclonal antibody to ICP 10 precipitated a 144-kDa protein from the transformed cells and stained them in immunofluorescence. A tumor derivative established with the transformed cells did not stain with this antibody, but approximately equal to 25% of the cells stained with a monoclonal antibody to c-myc protooncogene products.

The tyrosyl free radical in ribonucleotide reductase

The enzyme, ribonucleotide reductase, catalyses the formation of deoxyribonucleotides from ribonucleotides, a reaction essential for DNA synthesis in all living cells. The Escherichia coli ribonucleotide reductase, which is the prototype of all known eukaryotic and virus-coded enzymes, consists of two nonidentical subunits, proteins B1 and B2. The B2 subunit contains an antiferromagnetically coupled pair of ferric ions and a stable tyrosyl free radical. EPR studies show that the tyrosyl radical, formed by loss of ferric ions and a stable tyrosyl free radical. EPR studies show that the tyrosyl radical, formed by loss of an electron, has its unpaired spin density delocalized in the aromatic ring of tyrosine. Effects of iron-radical interaction indicate a relatively close proximity between the iron center and the radical. The EPR signal of the radical can be studied directly in frozen packed cells of E. coli or mammalian origin, if the cells are made to overproduce ribonucleotide reductase. The hypothetic role of the tyrosyl free radical in the enzymatic reaction is not yet elucidated, except in the reaction with the inhibiting substrate analogue 2'-azido-CDP. In this case, the normal tyrosyl radical is destroyed with concomitant appearance of a 2'-azido-CDP-localized radical intermediate. Attempts at spin trapping of radical reaction intermediates have turned out negative. In E. coli the activity of ribonucleotide reductase may be regulated by enzymatic activities that interconvert a nonradical containing form and the fully active protein B2. In synchronized mammalian cells, however, the cell cycle variation of ribonucleotide reductase, studied by EPR, was shown to be due to de novo protein synthesis. Inhibitors of ribonucleotide reductase are of medical interest because of their ability to control DNA synthesis. One example is hydroxyurea, used in cancer therapy, which selectively destroys the tyrosyl free radical.

Identification of the stable free radical tyrosine residue in ribonucleotide reductase. A sequence comparison

The small subunit of ribonucleoside diphosphate reductase contains a unique tyrosine radical and a binuclear iron center. An alignment of different primary structures of the small subunit in Escherichia coli, the marine mollusc Spisula solidissima, Epstein Barr and Herpes simplex viruses shows that regions comprising residues 115-122, 204-212 and 234-241 (in E.coli numbering) are strikingly similar and are likely to be recognized as functionally important. Two of 16 tyrosine residues and 2 of 8 histidine residues are conserved. We propose that Tyr-122 is responsible for radical stabilization and that His-118 and His-241 together with Glu-115 and Asp-237 or Glu-238 are ligands of the iron center.

Characterization of the gene encoding herpes simplex virus type 2 glycoprotein C and comparison with the type 1 counterpart

The gene encoding the glycoprotein C (gC) of herpes simplex virus type 1 maps to the region of the viral genome from 0.62 to 0.64. Recently, a herpes simplex virus type 2 glycoprotein previously designated gF and now designated gC was mapped to a homologous location. Analysis of the herpes simplex virus type 2 mRNA species encoded in this region revealed a major transcript of 2.5 kilobases, a 0.73-kilobase transcript (the 5' ends of which were mapped by primer extension), and several minor species, all nearly identical to the herpes simplex virus type 1 pattern. A polypeptide of ca. 60,000 daltons was identified by in vitro translation of hybrid-selected mRNA. A smaller protein of ca. 20,000 daltons was also mapped to this region. The nucleotide sequence of a 3.4-kilobase segment of DNA encompassing gC was determined, and an open reading frame of 1,440 nucleotides specifying a 480-amino acid protein with properties consistent with that of a glycoprotein was identified. Comparative DNA sequence analysis showed regions of limited homology within the coding sequences for gC and a deletion which results in 31 fewer amino acids in the gC-2 near the amino terminus of the protein. The carboxy termini of gC-1 and gC-2 are very similar, as are the 20,000-dalton proteins.

Herpes simplex virus types 1 and 2 homology in the region between 0.58 and 0.68 map units

The homology between herpes simplex virus type 1 and type 2 (HSV-1 and HSV-2, respectively) DNA between 0.58 and 0.674 map units was compared by Southern and dot blot analysis with DNA of one type of virus as a hybridization probe against the other type. Regions of high homology were interspersed with regions of detectably lower homology. However, only one region (between 0.647 and 0.653 map units) contained few or no homologous sequences. In situ RNA blot hybridization demonstrated that the mRNA species transcribed in the right-hand portion of the region are homologous between HSV-1 and HSV-2, as was previously found for the left-hand portion. A 2.7-kilobase HSV-2 transcript in the right-hand portion of the studied region was clearly that encoding HSV-2 glycoprotein C. Comparative nucleotide sequence analysis of specific regions demonstrated that homologous translational reading frames could be identified in the virus types. This analysis also demonstrated that homology could be abruptly lost outside such reading frames. Comparison of regions of homology with published HSV-1 transcription maps suggests that there can also be large divergence within translational reading frames. Some, but not complete, sequence homology was seen in the putative promoter sequence for the 730-base HSV-1 mRNA mapping to the right of glycoprotein C and the corresponding HSV-2 DNA. This suggests that the rather strict conservation of promoter sequences between homologous HSV-1 and HSV-2 transcripts seen in other regions of the genome may not be a necessary feature between these virus types.

Expression of recombinant genes containing herpes simplex virus delayed-early and immediate-early regulatory regions and trans activation by herpesvirus infection

The promoter-regulatory regions from the herpes simplex virus type 1 (HSV-1) gene for the immediate-early, 175,000-molecular-weight (175K) protein and the HSV-2 delayed-early gene for a 38K protein were linked to the readily assayable bacterial gene for the enzyme chloramphenicol acetyltransferase (CAT). Unexpectedly, in measurements of the constitutive expression of the recombinant genes 40 to 50 h after transfection of Vero cells, enzyme levels expressed from the delayed-early 38K-promoter-CAT construct (p38KCAT) were at least as high as those from the immediate-early 175K-promoter-CAT construct (p175KCAT). In contrast, enzyme levels expressed after transfection of a similar recombinant gene containing a second delayed-early promoter region, that of the HSV-1 thymidine kinase gene, were ca. 20-fold lower. The amounts of enzyme expressed from both p38KCAT and p175KCAT could be increased by up to 20- to 40-fold after infection of the transfected cells with HSV. In comparison, virus infection had no significant effect on enzyme levels expressed from recombinant CAT genes containing the simian virus 40 early promoter region, with or without the 72-base-pair enhancer element. Experiments with the temperature-sensitive mutants HSV-1 tsB7 and HSV-1 tsK indicate that induction of expression from p175KCAT was mediated by components of the infecting virus particle, whereas that from p38KCAT required de novo expression of virus immediate-early proteins. In addition, we show that functions required to induce expression from both p175KCAT and p38KCAT could also be provided by infection with pseudorabies virus and cytomegalovirus.

Characterization of mRNAs that map in the BglII N fragment of the herpes simplex virus type 2 genome

The BglII N DNA fragment (0.580 to 0.620 map units) of herpes simplex virus type 2 strain (333) is of interest because of its transforming potential. This fragment contains either partial or the complete coding sequences for nine mRNA transcripts that can be detected during a lytic infection. Subclones of the BglII N DNA fragment were generated in plasmid vectors, and the approximate locations of the mRNA transcripts were mapped by RNA blot hybridization technology. Precise 5' or 3' ends (or both) of these mRNA species were determined by S1 nuclease mapping, using the BglII N subclones as DNA probes. At least four mRNA transcripts are fully encoded in the BglII N fragment. The coding regions for all of the mRNA transcripts are densely packaged along the BglII N fragment with less than 150 base pairs between neighboring mRNA ends. Analysis of both neutral and alkaline gels failed to reveal the presence of any detectable introns. This manuscript reports a detailed transcription map for this region.

Small fragments of herpesvirus DNA with transforming activity contain insertion sequence-like structures

A 737-base-pair fragment of herpes simplex virus type 2 DNA with morphological-transforming ability was identified by transfecting into rodent cells deleted fragments of the left-hand end of the Bgl II N fragment region (map position 0.58-0.625), which were constructed in vitro. The transforming sequences lie within the coding region for a Mr 61,000 protein, but the fragment itself does not appear to specify a viral polypeptide. Contained within the transforming fragment are sequences that can be drawn as a stem-loop structure flanked by direct repeats, similar to an insertion sequence-like element. An insertion sequence-like structure was also found in a small fragment of human cytomegalovirus DNA that has transforming activity. Possible mechanisms of herpesvirus transformation are discussed.

Structural organization of human herpesvirus DNA molecules

The herpesviruses are among the largest and most complex of all DNA viruses, and their genomes display an astonishing diversity in size, structure, and organization. In 1974, the features of large inverted repeats and structural isomerization were first discovered, and these proved to be characteristic properties of many herpesvirus genomes. Since then, research using the powerful techniques of modern molecular biology has revealed a great deal of comparative structural information about the arrangement of repetitive sequences and the location, structure, and primary nucleotide sequences of the genes for several easily assayed or abundantly expressed gene products. Extensive restriction enzyme cleavage maps and complete sets of cloned DNA fragments have been constructed for each of the five human herpesviruses, HSV-1, HSV-2, CMV, EBV, and VZV, and the entire 175,000-bp nucleotide sequence of EBV DNA has been determined. Based on these maps and reagents, the procedures of "DNA fingerprinting" and "dot hybridization" are proving useful at a clinical level for characterization of isolates and studying herpesvirus epidemiology. Strain differences, localized heterogeneity, tandem-repeat-defective genomes, and sites of cell-virus DNA homology have been described in some detail. The attention of basic researchers is now turning to equating structure with function, and rapid progress is expected in studies aimed at a better understanding of the mechanisms of viral DNA replication, maintenance of the latent state, reactivation, transformation, packaging, and regulation of the lytic cycle, etc using cloned functionally active DNA fragments, isolated intact genes and promoters, and DNA transfection and in vitro expression systems.

HSV, CMV, and HPV in human neoplasia

We are studying the role of sexually transmitted viruses in the development of human tumors. The persistence of herpes simplex virus, cytomegalovirus, and human papillomavirus nucleic acid sequences has been examined using cloned viral DNA sequences as probes. The relationship of the viruses to various stages in the progression of neoplasia is examined, with particular reference to the role of viral and/or cellular genes in the initiation, promotion, and maintenance of the neoplastic phenotype. The human tumors of major interest in this context are carcinomas of the cervix, vulva, and anus and Kaposi's sarcoma. The minimal fragment of HSV-2 DNA detected in cervical tumors is contained within a 656-bp sequence that can be used in transfection experiments to transform rodent cells in vitro to a malignant phenotype. However, neither this fragment nor any other is consistently retained in cervical tumors, suggesting that this viral DNA may initiate but not maintain the transformed phenotype.