Control of expression of the vaccinia virus thymidine kinase gene

Construction of recombinant capripoxviruses as vaccine vectors for delivering foreign antigens: Methodology and application

Goatpox (GTP), sheeppox (SPP) and lumpy skin disease (LSD) are three severe diseases of goat, sheep and cattle. Their typical clinical symptoms are characterized by vesicles, papules, nodules, pustules and scabs on animal skins. The GTP, SPP and LSD are caused by goatpox virus (GTPV), sheeppox virus (SPPV) and lumpy skin disease virus (LSDV), respectively, all of which belong to the genus Capripoxvirus in the family Poxviridae. Several capripoxvirus (CaPV) isolates have been virulently attenuated through serial passaging in vitro for production of live vaccines. CaPV-based vector systems have been broadly used to construct recombinant vaccines for delivering foreign antigens, many of which have been demonstrated to induce effective immune protections. Homologous recombination is the most commonly used method for constructing recombinant CaPVs. Here, we described a methodology for generation of recombinant CaPVs by the homologous recombination, and further reviewed CaPV-vectored vaccines for delivering foreign antigens.

Targeting Nucleotide Biosynthesis: A Strategy for Improving the Oncolytic Potential of DNA Viruses

The rapid growth of tumors depends upon elevated levels of dNTPs, and while dNTP concentrations are tightly regulated in normal cells, this control is often lost in transformed cells. This feature of cancer cells has been used to advantage to develop oncolytic DNA viruses. DNA viruses employ many different mechanisms to increase dNTP levels in infected cells, because the low concentration of dNTPs found in non-cycling cells can inhibit virus replication. By disrupting the virus-encoded gene(s) that normally promote dNTP biosynthesis, one can assemble oncolytic versions of these agents that replicate selectively in cancer cells. This review covers the pathways involved in dNTP production, how they are dysregulated in cancer cells, and the various approaches that have been used to exploit this biology to improve the tumor specificity of oncolytic viruses. In particular, we compare and contrast the ways that the different types of oncolytic virus candidates can directly modulate these processes. We limit our review to the large DNA viruses that naturally encode homologs of the cellular enzymes that catalyze dNTP biogenesis. Lastly, we consider how this knowledge might guide future development of oncolytic viruses.

Database on natural polymorphisms and resistance-related non-synonymous mutations in thymidine kinase and DNA polymerase genes of herpes simplex virus types 1 and 2

The use of genotypic resistance testing of herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) is increasing because the rapid availability of results significantly improves the treatment of severe infections, especially in immunocompromised patients. However, an essential precondition is a broad knowledge of natural polymorphisms and resistance-associated mutations in the thymidine kinase (TK) and DNA polymerase (pol) genes, of which the DNA polymerase (Pol) enzyme is targeted by the highly effective antiviral drugs in clinical use. Thus, this review presents a database of all non-synonymous mutations of TK and DNA pol genes of HSV-1 and HSV-2 whose association with resistance or natural gene polymorphism has been clarified by phenotypic and/or functional assays. In addition, the laboratory methods for verifying natural polymorphisms or resistance mutations are summarized. This database can help considerably to facilitate the interpretation of genotypic resistance findings in clinical HSV-1 and HSV-2 strains.

Host factor SAMHD1 restricts DNA viruses in non-dividing myeloid cells

SAMHD1 is a newly identified anti-HIV host factor that has a dNTP triphosphohydrolase activity and depletes intracellular dNTP pools in non-dividing myeloid cells. Since DNA viruses utilize cellular dNTPs, we investigated whether SAMHD1 limits the replication of DNA viruses in non-dividing myeloid target cells. Indeed, two double stranded DNA viruses, vaccinia and herpes simplex virus type 1, are subject to SAMHD1 restriction in non-dividing target cells in a dNTP dependent manner. Using a thymidine kinase deficient strain of vaccinia virus, we demonstrate a greater restriction of viral replication in non-dividing cells expressing SAMHD1. Therefore, this study suggests that SAMHD1 is a potential innate anti-viral player that suppresses the replication of a wide range of DNA viruses, as well as retroviruses, which infect non-dividing myeloid cells.

Various viral pathogens such as HIV-1, herpes simplex virus (HSV) and vaccinia virus infect terminally-differentiated/non-dividing macrophages during the course of viral pathogenesis. Unlike dividing cells, non-dividing cells lack chromosomal DNA replication, do not enter the cell cycle, and harbor very low levels of cellular dNTPs, which are substrates of viral DNA polymerases. A series of recent studies revealed that the host protein SAMHD1 is dNTP triphosphohydrolase, which contributes to the poor dNTP abundance in non-dividing myeloid cells, and restricts proviral DNA synthesis of HIV-1 and other lentiviruses in macrophages, dendritic cells, and resting T cells. In this report, we demonstrate that SAMHD1 also controls the replication of large dsDNA viruses: vaccinia virus and HSV-1, in primary human monocyte-derived macrophages. SAMHD1 suppresses the replication of these DNA viruses to an even greater extent in the absence of viral genes that are involved in dNTP metabolism such as thymidine kinase. Therefore, this study supports that dsDNA viruses evolved to express enzymes necessary to increase the levels of dNTPs as a mechanism to overcome the restriction induced by SAMHD1 in myeloid cells.

Evaluation of a UCMK/dCK fusion enzyme for gemcitabine-mediated cytotoxicity

While gemcitabine (2'-2'-difluoro-2'-deoxycytidine, dFdC) displays wide-ranging antineoplastic activity as a single agent, variable response rates and poor intracellular metabolism often limit its clinical efficacy. In an effort to enhance dFdC cytotoxicity and help normalize response rates, we created a bifunctional fusion enzyme that combines the enzymatic activities of deoxycytidine kinase (dCK) and uridine/cytidine monophosphate kinase (UCMK) in a single polypeptide. Our goal was to evaluate whether the created fusion could induce beneficial, functional changes toward dFdC, expedite dFdC conversion to its active antimetabolites and consequently amplify cell dFdC sensitivity. While kinetic analyses revealed the UCMK/dCK fusion enzyme to possess both native activities, the fusion rendered cells sensitive to the cytotoxic effects of dFdC at the same level as dCK expression alone. These results suggest that increased wild-type UCMK expression does not provide a significant enhancement in dFdC-mediated cytotoxicity and may warrant the implementation of studies aimed at engineering UCMK variants with improved activity toward gemcitabine monophosphate.

The effect of nitric oxide on vaccinia virus-encoded ribonucleotide reductase

Growth inhibition of the DNA virus vaccinia (VACV) by NO is known to occur at the level of DNA synthesis. This inhibition is partially reversed by addition of deoxyribonucleosides, suggesting that NO or NO-related species inhibit viral ribonucleotide reductase (RR). However, the effect of NO on VACV-encoded RR or other DNA-synthesizing enzymes has not been demonstrated. In order to study the effects of NO on VACV-encoded RR, DNA polymerase (DNA pol) and thymidine kinase (TK), we generated a VACV recombinant expressing murine macrophage iNOS under control of a VACV early/late promoter p7.5. Using this recombinant, we demonstrate that expression of iNOS and the resulting production of NO inhibit activity of the viral RR, but not of viral DNA pol and TK. This NO-mediated inhibition of viral RR occurred around the same time as the increase of ADP levels, while it preceded the block in VACV DNA synthesis and the decrease of ATP levels. In addition, we tested the effects of DPTA/NONOate on the growth of different VACV mutants. Fold-inhibition of the growth of VACV deletion mutant for TK was comparable to that of wild-type VACV. VACV containing amplification of the gene for the small subunit of RR appeared to be least sensitive to DPTA/NONOate, while VACV deletion mutant for the large subunit of RR was most sensitive. The results provide a direct evidence for NO-mediated inhibition of VACV-encoded RR.

Biophysical characterization of vaccinia virus thymidine kinase substrate utilization

To provide information for the development of new antiviral compounds that inhibit orthopoxviruses, further characterization of the kinetics and thermodynamics that underlie substrate utilization reactions of vaccinia virus thymidine kinase (VVTK) has been undertaken. The kinetics of 2'deoxythymidine phosphorylation by VVTK and the thermodynamics of complex formation between VVTK and the substrate 2' deoxythymidine were determined using spectroscopic and calorimetric techniques. These studies demonstrated that kinetic parameters for 2' deoxythymidine phosphorylation by VVTK were 25 microM and 0.2s(-1) for K(m) and k(cat), respectively. The enthalpy change, Delta H, for the enzyme catalyzed reaction is -18.1 kcal/mol. Thermodynamic studies for the formation of the enzyme substrate complex demonstrated a binding affinity (K(a)) of 4 x 10(4)M(-1), an enthalpy change for binding (Delta H) of -17.4 kcal/mol, and a reaction stoichiometry of two molecules of substrate binding to each enzyme tetramer. Kinetic and thermodynamic data were in agreement (K(a) approximately 1/K(m)) and showed similarities to literature values reported for herpes simplex virus thymidine kinase (HSV-TK) and human thymidine kinase 1 (hTK1) with respect to k(cat) but not with respect to K(m). The K(m) value found for VVTK in this study is nearly two orders of magnitude larger than the values reported for the hTK1 and the HSV TK enzymes.

A consideration of previously uncharacterized fowl poxvirus unidirectional and bidirectional late promoters for inclusion in homologous recombinant vaccines

Because of the limited analysis of fowl poxvirus (FPV) promoters, expression of foreign proteins by recombinant FPV has usually been directed by heterologous vaccinia virus or synthetic poxvirus promoters. Thus, the impact of completely homologous recombinant virus vaccines has yet to be realized by the poultry industry. In an effort to increase the availability of such transcriptional regulatory elements, the modulation of gene expression by six previously uncharacterized FPV late promoters was examined. To simplify this comparison, each promoter region was separately coupled to the same reporter gene (lacZ) in individual plasmid constructs, and their activities in transfected, virus-infected cells were monitored. In each of the four selected unidirectional transcriptional regulatory elements as well as a 30-base pair representative of the bidirectional promoter region, the predicted temporal specificity of expressing at late stages of virus replicative cycle was verified. Stable lacZ gene transcripts arising from each plasmid varied less than threefold in quantity, whereas the amounts of beta-galactosidase product ranged within a 130-fold interval. Only the promoter that naturally regulates expression of the A type inclusion body protein gene directed production of beta-galactosidase at a level comparable with that associated with the strong vaccinia virus P11 promoter. Because one of the remaining unidirectional transcriptional regulatory elements, P174, was only 2.4-fold less efficient, both of these promoters, P174 and P190, should be satisfactory for directing the expression of poultry pathogen genes inserted into the genomes of FPV recombinant vaccines.

The eukaryotic translation initiation factor 4E is not modified during the course of vaccinia virus replication

The ability of vaccinia virus to inhibit processes of cap-dependent translational initiation by inactivating the eukaryotic translation initiation factor 4E (eIF-4E) has been examined. Analyses of the quantities of eIF-4E present in either uninfected mouse L929 cells or vaccinia virus-infected cells showed that during the first 12 hr of virus replication, when there is a marked decrease in host gene expression in infected cells, there is no change in the total amount of eIF-4E present. Analyses of eIF-4E that was metabolically labeled with [32P] and then purified by affinity chromatography using m7GTP-Sepharose 4B, indicated that neither the incorporation of radiolabel into eIF-4E nor the amounts of eIF-4E capable of binding to cap structures changed significantly during virus replication. Immunodetection of phosphorylated and unphosphorylated eIF-4E in cell lysates fractionated by two-dimensional gel electrophoresis showed that the steady-state levels of phosphorylated and unphosphorylated forms of eIF-4E were similar in uninfected and virus-infected cells. These results suggest that vaccinia virus does not gain preferential translation of viral mRNAs over other mRNAs in the cell by reducing either eIF-4E phosphorylation or its ability to bind to the cap structure.

Isolation and molecular characterization of the swinepox virus thymidine kinase gene

Swinepox virus (SPV), the only member of the Suipoxvirus genus, shows little antigenic relatedness or DNA homology to members of the other poxvirus genera. A SPV thymidine kinase (TK) gene was detected and mapped to the left end of the HindIII G fragment using degenerate oligonucleotide probes. Cloning and sequencing of a 1.8-kb HindIII-BamHI fragment containing the SPV TK gene revealed an open reading frame (ORF) of 181 amino acids yielding a predicted polypeptide of Mr 20.6 kDa with significant homology to both poxvirus and vertebrate thymidine kinases. Comparison with other TK protein sequences showed that the SPV thymidine kinase was closely related to the TK genes of avipoxviruses (52.0%) and vertebrates (57.1-59.7%). The TK gene from African swine fever virus (ASF) showed little homology (30.5%) to the SPV TK gene suggesting that these two viruses are not closely related though they share many biochemical features and infect a single, common mammalian host (swine). The SPV TK gene, like that of other poxviruses, is transcribed early, and when cloned into a TK- strain of vaccinia converted the virus to a TK+ phenotype. BUdRR mutants of SPV contained frameshift, deletion, and missense mutations in the TK ORF.

Assembly and analysis of a functional vaccinia virus "amplicon" containing the C-repeat region from the M protein of Streptococcus pyogenes

Previous studies have shown that when inoculated intranasally into mice, vaccinia virus (VV) recombinants expressing the carboxyl half of the Streptococcus pyogenes M protein [which contains the C-repeat region (CRR)] could elicit a protective immune response against subsequent challenge by both homologous and heterologous serotypes of pathogenic group A streptococci. In the present study, an insertion plasmid was constructed that contained three tandem in-frame repeats of a 310-base-pair DNA sequence encoding the CRR from streptococcal M6 protein under control of a constitutive viral promoter. The plasmid was used to introduce the bacterial sequences into the VV genome by homologous recombination. Surprisingly, the recombinant VV:CRR3X virus that was isolated appeared to represent not an individual recombinant virus but a complex mixture of variants that contained from 1 to greater than 20 tandem copies of the CRR region at the insertion site. This genomic complexity was mirrored at the transcriptional level in that a nested set of coterminal transcripts was detected in VV:CRR3X-infected cells, which increased in size from 1400 to 6600 bases by increments of approximately 300 bases. All transcripts containing two or more CRR inserts appeared functional, as Western (immuno) blot analyses of VV:CRR3X-infected cell extracts revealed a family of CRR-related proteins with apparent molecular masses that increased from 30 kDa upward in increments of 10 kDa. All data are consistent with the hypothesis that variation in the VV:CRR3X recombinants is from random crossover events that occur within the CRR region during viral DNA replication. These results suggest that the genomic diversity generated by the "recombinogenic" properties of vaccinia recombinants containing tandem foreign inserts could be used to facilitate induction of a broadly protective immune response against antigenically diverse pathogenic agents.

Nucleotide sequence analysis of the bovine respiratory syncytial virus fusion protein mRNA and expression from a recombinant vaccinia virus

Bovine respiratory syncytial (BRS) virus is an important cause of serious respiratory illness in calves. The disease caused in calves is similar to that caused by human respiratory syncytial (HRS) virus in children. The two viruses, however, have distinct host ranges and the attachment glycoproteins, G, have no antigenic cross-reactivity. The fusion glycoproteins, F, of the HRS and BRS viruses, however, have some antigenic cross-reactivity. To further compare the BRS virus and HRS virus fusion proteins, we determined the nucleotide sequence of cDNA clones to the BRS virus F protein mRNA, deduced the amino acid sequence, and compared these sequences with the HRS virus F protein sequences. The BRS virus F mRNA was 1899 nucleotides in length and had a single major open reading frame which could code for a polypeptide of 574 amino acids with an estimated molecular weight of 63.8 kDa. Structural features predicted from the amino acid sequence included an NH2-terminal signal sequence (residues 1-26), a site for proteolytic cleavage (residues 131-136) to generate the disulfide-linked F1 and F2 subunits, and a hydrophobic transmembrane anchor sequence (residues 522-549). The nucleic acid identity between the BRS virus and the HRS virus F mRNA sequences was 71.5%. The predicted BRS virus F protein shared 80.5% overall amino acid identity with the HRS virus F protein with 89% identity in the F1 polypeptide but only 68% identity in the F2 polypeptide. The position and number of the cysteine residues in the F1 and F2 polypeptides were conserved among all F proteins. However, BRS virus F protein had only three potential N-linked carbohydrate acceptor sites in comparison to four or five for the HRS viruses. A difference in the extent of glycosylation between the BRS and HRS virus F2 polypeptides was shown to be responsible for differences observed in the electrophoretic mobility of these proteins. A cDNA containing the complete open reading frame of the BRS virus F mRNA was inserted into the thymidine kinase gene of vaccinia virus and following homologous recombination, a recombinant virus containing the BRS virus F gene was isolated. The BRS virus F protein was expressed in recombinant virus infected cells as demonstrated by immunoprecipitation and was transported to and expressed on the surface of infected cells as shown by indirect immunofluorescence.

Nucleotide sequence of the Escherichia coli thymidine kinase gene provides evidence for conservation of functional domains and quaternary structure

Using lambda bacteriophage clones from the Kohara Escherichia coli library spanning minutes 25.5 to 28.5 on the E. coli chromosome (strain W3110), two overlapping DNA fragments were identified which were able to confer thymidine kinase (TK) enzyme activity to a TK- strain of E. coli (KY895). This genetic complementation assay was used in concert with subcloning procedures to identify the minimal region (a 900 bp EcoRI-SalI fragment) which contained the E. coli thymidine kinase gene (tdk). The nucleotide sequence of the EcoRI-SalI fragment and a small portion of the adjoining downstream fragment was determined. Computer analysis of the derived sequence indicated the presence of a rightward-reading open reading frame of 615 bp which was capable of encoding a 205-amino-acid polypeptide with a predicted Mr of 23458 daltons. The in vivo transcriptional activity of this locus was confirmed by Northern blot hybridization analysis of RNA isolated from E. coli JM101 or KY895 which detected a 650-nucleotide RNA transcribed from this region. This places the tdk gene at approximately minute 27.35 on the E. coli W3110 chromosome, about 15 kb downstream from the narG locus and approximately 25 kb upstream of the trp operon. Although the predicted Mr of the E. coli TK protein was 23.5 kDa, gel-filtration analyses suggested that, like eukaryotic thymidine kinases, the active form of this enzyme is a multimeric complex.(ABSTRACT TRUNCATED AT 250 WORDS)

Nucleotide sequence analysis and expression from recombinant vectors demonstrate that the attachment protein G of bovine respiratory syncytial virus is distinct from that of human respiratory syncytial virus

Bovine respiratory syncytial (BRS) virus causes a severe lower respiratory tract disease in calves similar to the disease in children caused by human respiratory syncytial (HRS) virus. While there is antigenic cross-reactivity among the other major viral structural proteins, the major glycoprotein, G, of BRS virus and that of HRS virus are antigenically distinct. The G glycoprotein has been implicated as the attachment protein for HRS virus. We have carried out a molecular comparison of the glycoprotein G of BRS virus with the HRS virus counterparts. cDNA clones corresponding to the BRS virus G glycoprotein mRNA were isolated and analyzed by dideoxynucleotide sequencing. The BRS virus G mRNA contained 838 nucleotides exclusive of poly(A) and had a major open reading frame coding for a polypeptide of 257 amino acid residues. The deduced amino acid sequence of the BRS virus G polypeptide showed only 29 to 30% amino acid identity with the G protein of either the subgroup A or B HRS virus. However, despite this low level of identity, there were strong similarities in the predicted hydropathy profiles of the BRS virus and HRS virus G proteins. A cDNA molecule containing the complete BRS virus G major open reading frame was inserted into the thymidine kinase gene of vaccinia virus by homologous recombination, and a recombinant virus containing the BRS virus G protein gene was isolated. This recombinant virus expressed the BRS virus G protein, as demonstrated by Western immunoblot analysis and immunofluorescence of infected cells. The BRS virus G protein expressed from the recombinant vector was transported to and expressed on the surface of infected cells. Antisera to the BRS virus G protein made by using the recombinant vector to immunize animals recognized the BRS virus attachment protein but not the HRS virus G protein and vice versa, confirming the lack of antigenic cross-reactivity between the BRS and HRS virus attachment proteins. On the basis of the data presented here, we conclude that BRS virus should be classified within the genus Pneumovirus in a group separate from HRS virus and that it is no more closely related to HRS virus subgroup A than it is to HRS virus subgroup B.

Vaccinia virus vectors: new strategies for producing recombinant vaccines

The development and continued refinement of techniques for the efficient insertion and expression of heterologous DNA sequences from within the genomic context of infectious vaccinia virus recombinants are among the most promising current approaches towards effective immunoprophylaxis against a variety of protozoan, viral, and bacterial human pathogens. Because of its medical relevance, this area is the subject of intense research interest and has evolved rapidly during the past several years. This review (i) provides an updated overview of the technology that exists for assembling recombinant vaccinia virus strains, (ii) discusses the advantages and disadvantages of these approaches, (iii) outlines the areas of outgoing research directed towards overcoming the limitations of current techniques, and (iv) provides some insight (i.e., speculation) about probable future refinements in the use of vaccinia virus as a vector.

DNA sequences that regulate expression of a vaccinia virus late gene (L65) and interact with a DNA-binding protein from infected cells

To be efficiently expressed in vivo, the vaccinia virus late gene, L65, requires 5'-proximal cis-acting elements which bind a factor from infected cells. Deletion mutagenesis and vaccinia virus helper-dependent transient expression procedures were used to demonstrate that two distinct late promoter elements direct transcription from two different start sites (proximal [+1] and distal [-92]). The -128 to -112 region was essential for L65 distal promoter function, while sequences between -59 and +50 were sufficient for L65 proximal promoter function. The proximal DNA sequences interact with a protein, binding factor I (BF-I), which was isolated and partially purified from vaccinia virus-infected cells at late times postinfection. This activity is not detectable in uninfected cells or in purified virions. This factor binds specifically to two different sites within the proximal promoter, one 5' and one 3' to the transcription start site, but does not bind to the distal promoter element.

Expression vector pT7:TKII for the synthesis of authentic biologically active RNA encoding vaccinia virus thymidine kinase

A transcription vector, pT7: TKII, was constructed by a novel application of the polymerase chain reaction. Chimeric oligodeoxynucleotides were used to direct the synthesis of a DNA fragment which consisted of a truncated bacteriophage T7 promoter element fused to the vaccinia virus (VV) thymidine kinase gene (tk). This fragment was cloned into a pUC118 plasmid and sequenced to ensure no mutations had occurred during its synthesis. When linearized at the 3' end of the VV tk gene at the BamHI site located in the polylinker region of the vector, pT7:TKII was efficiently transcribed by T7 RNA polymerase into a 595 nucleotide transcript whose 5' end was identical to that found on authentic nascent VV tk mRNA. When translated in a rabbit reticulocyte lysate system, the synthetic VV tk RNA was shown to be biologically active in that it directed the synthesis of a 20-kDa protein which assembled into an enzymatically active 80-kDa tetrameric complex which was indistinguishable from VV thymidine kinase (TK) enzyme isolated from VV-infected cells. The pT7:TKII vector provides a powerful approach with which: (i) to investigate the translational and posttranslational regulation of the VV tk gene; (ii) to use directed genetics to identify potential cis-acting regulatory sequences or structures present within the VV tk RNA; and (iii) to apply protein engineering procedures to identify the catalytic, allosteric and subunit interactive domains of the VV TK enzyme. As an example, the translational effects of adding a m7G cap structure to the pT7:TKII-derived VV tk RNA are presented.

Antibodies directed against a synthetic peptide enable detection of a protein encoded by a vaccinia virus host range gene that is conserved within the Orthopoxvirus genus

A vaccinia virus gene required for multiplication in some cell lines but not in others has been previously isolated and sequenced. A synthetic peptide predicted from the nucleotide sequence and corresponding to the carboxy-terminal 18 amino acids was used to raise antibodies in rabbits. The immune serum enabled detection of a 29-kilodalton (kDa) polypeptide by either immunoprecipitation or Western immunoblot assays. Synthesis of the 29-kDa polypeptide occurred immediately after infection and lasted for about 3 h. Shutoff of its synthesis was concomitant with the appearance of a delayed early polypeptide that may be antigenically related to the 29-kDa polypeptide. Analysis of cloned segments of the genomes of other orthopoxviruses by hybridization with the vaccinia virus host range gene demonstrates that it is well conserved within this genus.

Expression of herpes simplex virus thymidine kinase, mediated by vaccinia virus early promoters

We measured herpes virus thymidine kinase (HSV-TK) activity in extracts from cells infected with eight vaccinia virus recombinants (VpT), each expressing HSV-TK under the control of an early promoter previously isolated by a shotgun procedure. The HSV-TK activities induced by the VpT recombinants were compared to that produced under the control of the vaccinia virus thymidine kinase (VV-TK) promoter in VMM5-TK recombinant virus. The insert from VpT38 was approximately 10 times more efficient than the VV-TK promoter for HSV-TK expression, reflecting a similar relative strength of the promoters. HSV-TK activities induced by the other VpT recombinants varied between one and ten times that expressed by the VV-TK promoter, but the nucleotide sequence of the 5'-end region of their mRNA suggested that these values did not necessarily reflect the strength of corresponding promoters. No significant reduction in HSV-TK activity was noted for two VpT and the VMM5-TK recombinants when viral DNA replication was prevented, but a significant reduction (30 to 75%) was observed for the other six recombinants studied. These results suggested that some early genes of vaccinia virus are expressed only during the early stage of infection, whereas others continue to be expressed at the late stage. The strength of two vaccinia early promoters (VpT38, PF) relative to that of the VV-TK promoter was deduced from HSV-TK activities induced by comparable vaccinia virus recombinants.

Characterization of a binding factor that interacts with the sequences upstream of the vaccinia virus thymidine kinase gene

A small 176 base-pair cloned DNA fragment, representing the nucleotide sequences proximal to the 5'-end of the vaccinia virus thymidine kinase (VV TK) gene, was radiolabeled and used in concert with gel retention assays to detect, partially purify, and characterize a promoter binding factor (PBF) extracted from vaccinia virions. The VV TK PBF was purified from solubilized virus particles by a combination of ion-exchange and DNA-affinity chromatographic procedures. The interaction between VV TK PBF and VV TK promoter sequences was relatively specific in that binding to the radiolabeled probe could be effectively inhibited by unlabeled VV TK promoter or VV TK promoter-specific oligonucleotides, but not by similar-sized fragments of control plasmid DNA. The VV TK PBF did, however, bind to other VV early-promoter elements. Glycerol gradient sedimentation provided an estimate of 130-140 kD for the native molecular weight of VV PBF. This correlated well with data from the purification of VV PBF from radiolabeled VV particles that revealed 2 polypeptides, with molecular weights of 70 and 68 kD that co-purified with VV TK PBF activity. Taken together, these results suggest that a heterodimeric promoter-binding factor, which is present within the cytoplasm of VV-infected cells, is capable of specifically interacting with VV early-promoter elements.

Nucleotide sequence and molecular genetic analysis of the vaccinia virus HindIII N/M region encoding the genes responsible for resistance to alpha-amanitin

The genomic location of the gene(s) which provides vaccinia virus (VV) alpha-amanitin-resistant mutants with a drug-resistant phenotype have been mapped to the HindIII N/M region of the genome by the use of marker rescue techniques [E. C. Villarreal and D. E. Hruby (1986) J. Virol. 57, 65-70]. Nucleotide sequencing of a 2356-bp HindIII-Sau3A fragment of the vaccinia virus genome encompassing this region reveals the presence of two complete leftward-reading open reading frames (ORFs, N2 and M1) and two incomplete ORFs (N1 and M2). By computer analysis the N2 and M1 ORFs would be predicted to encode soluble VV polypeptides with molecular weights of approximately 20 and 48 kDa, respectively. The N2 and M1 ORFs have extremely A-T-rich 5'-proximal sequences, consistent with previous data regarding the location and A-T-richness of viral early promoters. Likewise, the consensus signal believed to be involved in terminating VV early gene transcription, TTTTTNT, was evident at the 3'-boundary of both the N2 and M1 ORFs suggesting that these genes may be VV early genes. The in vivo transcriptional activity, orientation, and limits of these putative transcriptional units were investigated by Northern blot, nuclease S1, and primer extension analysis. Both N2- and M1-specific transcripts were detected in the cytoplasm of VV-infected cells, suggesting that these loci are bonafide viral genes. Time-course nuclease S1 experiments revealed that the N2 gene was transcribed exclusively prior to VV DNA replication. In contrast, the M1 gene was transcribed throughout infection, although different start sites were used at early versus late times postinfection. These results are discussed in relation to the drug-resistant phenotype and future experiments to identify the viral gene product responsible.

Inhibition of vaccinia virus replication by nicotinamide: evidence for ADP-ribosylation of viral proteins

Replication of vaccinia virus (VV) in monolayers of BSC40 cells was inhibited 99.9% in the presence of 60 mM nicotinamide (NIC), a competitive inhibitor of ADP-ribosylation reactions. Dot-blot hybridization analysis of infected cell extracts utilizing a VV DNA-specific probe indicated that the drug had only minimal effects on viral DNA synthesis. SDS-polyacrylamide gel electrophoresis of newly synthesized VV proteins pulse-labeled at early (2 h) or late (8 h) times post-infection revealed that although the full spectrum of expected viral polypeptides was evident, quantitative differences in the levels of expression of a distinct subset of viral proteins were observed in the presence of the drug. Velocity sedimentation of virus-infected cell lysates established that no mature particles were assembled in drug treated cells. Additional evidence suggesting that VV morphogenesis was abortive in the presence of NIC was obtained by pulse-chase labeling experiments that demonstrated that the two VV major late core polypeptide precursors P94 and P65, whose proteolytic processing to VP62 and VP60 is intimately associated with viral assembly, were not cleaved in the presence of NIC. Interestingly, growth of VV in the presence of [3H]adenosine resulted in the metabolic labeling of eight proteins that were associated with purified virions. These proteins co-migrated with proteins labeled with [3H]adenosine that were present in extracts of VV-infected, but not uninfected, cells. These analyses also revealed that the [3H]adenosine-labeling of a subset of cellular proteins (MW 18-20 kDa, possibly histones) was increased 4-fold by VV infection. The observed induction of either increased synthesis or hyper-modification of these 18-20 kDa proteins was inhibited by NIC. These results are discussed with respect to whether one or more VV polypeptides are subject to obligatory ADP-ribosylation modification reactions in order to attain their active configuration, and if so, whether the enzymes catalyzing these reactions are specified by the virus or host cell.

Vaccinia virus produces late mRNAs by discontinuous synthesis

We describe the unusual structure of a vaccinia virus late mRNA. In these molecules, the protein-coding sequences of a major late structural polypeptide are preceded by long leader RNAs, which in some cases are thousands of nucleotides long. These sequences map to different regions of the viral genome and in one instance are separated from the late gene by more than 100 kb of DNA. Moreover, the leader sequences map either upstream or downstream of the late gene, are transcribed from either DNA strand, and are fused to the late gene coding sequence via a poly(A) stretch. This demonstrates that vaccinia virus produces late mRNAs by tagging the protein-coding sequences onto the 3' end of other RNAs.

High-frequency homologous recombination in vaccinia virus DNA

A recombinant vaccinia virus genome was constructed in which the viral thymidine kinase (tk) gene was placed between direct repeats of a 1.5-kilobase-pair DNA sequence of heterologous origin. When forced to replicate in tk- cells in the presence of methotrexate (i.e., under tk+-selective conditions), the recombinant maintained its tk+ phenotype. Under nonselective conditions, however, the tk gene was frequently excised by both inter- and intramolecular recombination events because the repeated sequences provided substantial targets for homologous DNA recombination. Unique DNA products of intramolecular recombination were detected in the cytoplasm of infected cells soon after the onset of viral DNA replication, and their appearance was blocked by inhibitors of DNA synthesis. During repeated passage of the virus under nonselective conditions, the tk+ fraction decreased with first-order kinetics at a rate that reflected the frequency of recombination per cycle of virus replication. Eventually, a residual population of stable tk+ viruses remained, and analyses of the genome structures of individual members of this population showed that some of them appeared to be the products of nonhomologous DNA recombination.

Nucleotide sequence and transcript organization of a region of the vaccinia virus genome which encodes a constitutively expressed gene required for DNA replication

A vaccinia virus (VV) gene required for DNA replication has been mapped to the left side of the 16-kilobase (kb) VV HindIII D DNA fragment by marker rescue of a DNA- temperature-sensitive mutant, ts17, using cloned fragments of the viral genome. The region of VV DNA containing the ts17 locus (3.6 kb) was sequenced. This nucleotide sequence contains one complete open reading frame (ORF) and two incomplete ORFs reading from left to right. Analysis of this region at early times revealed that transcription from the incomplete upstream ORF terminates coincidentally with the complete ORF encoding the ts17 gene product, which is directly downstream. The predicted proteins encoded by this region correlate well with polypeptides mapped by in vitro translation of hybrid-selected early mRNA. The nucleotide sequences of a 1.3-kb BglII fragment derived from ts17 and from two ts17 revertants were also determined, and the nature of the ts17 mutation was identified. S1 nuclease protection studies were carried out to determine the 5' and 3' ends of the transcripts and to examine the kinetics of expression of the ts17 gene during viral infection. The ts17 transcript is present at both early and late times postinfection, indicating that this gene is constitutively expressed. Surprisingly, the transcriptional start throughout infection occurs at the proposed late regulatory element TAA, which immediately precedes the putative initiation codon ATG. Although the biological activity of the ts17-encoded polypeptide was not identified, it was noted that in ts17-infected cells, expression of a nonlinked VV immediate-early gene (thymidine kinase) was deregulated at the nonpermissive temperature. This result may indicate that the ts17 gene product is functionally required at an early step of the VV replicative cycle.

Quantitative assay of recombinant vaccinia virus-encoded neomycin phosphotransferase in infected eukaryotic cell lysates

A method for the detection and quantitation of neomycin phosphotransferase (NPT II) activity in recombinant vaccinia virus (VV)-infected eukaryotic cell lysates is described. The assay is linear with respect to both protein concentration and time of incubation. Cytoplasmic extracts of cells infected with a recombinant VV expressing the bacterial neo gene exhibited NPT II levels more than 50-fold higher than those detected in extracts from either uninfected or VV-infected cells. These results indicate that interference from cellular or viral-induced ATPase activities is sufficiently low that NPT II enzyme activity can be measured in crude cell lysates without employing additional protein purification procedures.

Determination of the promoter region of an early vaccinia virus gene encoding thymidine kinase

Nine recombinant vaccinia viruses that contain overlapping segments of the putative promoter region of the vaccinia virus thymidine kinase (TK) gene linked to DNA coding for the prokaryotic enzyme chloramphenicol acetyltransferase (CAT) were constructed. In each case, the RNA start site and 5 bp of DNA downstream were retained. No significant difference in CAT expression occurred as the deletion was extended from 352 to 32 bp before the RNA start site. Deletion of a further 10 bp, however, led to complete cessation of early promoter activity. Primer extension analysis of the 5' ends of the transcripts verified that the natural TK RNA start site was still used when only 32 bp of upstream DNA remained. Loss of early promoter activity was previously found when deletions were extended from 31 to 24 bp before the RNA start site of another vaccinia gene that is expressed constitutively throughout infection (M.A. Cochran, C. Puckett, and B. Moss, 1985, Proc. Natl. Acad. Sci. USA 82, 19-23). Sequence similarities in the promoter regions of these two genes were noted.

Expression of the fusion protein of human respiratory syncytial virus from recombinant vaccinia virus vectors and protection of vaccinated mice

Vaccinia virus (VV) recombinants were constructed that contained full-length cDNA copies of the fusion (F) protein gene of human respiratory syncytial (RS) virus. The F protein gene was placed next to the strong early-late VV 7.5-kilodalton promoter and was located within the VV thymidine kinase (tk) gene. Full-length recombinant transcripts that initiated at both the tk and the 7.5-kilodalton promoters accumulated in cells early in infection, and one or more of these transcripts was translated to yield a glycoprotein which comigrated with Fo, the fusion protein precursor. This precursor was processed by proteolytic cleavage to produce the two disulfide-linked subunits F1 and F2, which were both glycosylated and of the same electrophoretic mobility as authentic F1 and F2. Immunofluorescence studies demonstrated that the mature F protein was transported to and expressed on the surface of recombinant VV-infected cells. Inoculation of rabbits with a recombinant vector expressing F resulted in the production of antiserum specific for the RS virus F protein. This antiserum neutralized virus infectivity and was capable of preventing fusion in RS virus-infected cells. Mice were vaccinated with recombinants expressing the F protein. At 3 weeks postinoculation, these animals had serum antibody against RS virus F protein. At 5 days after intranasal challenge with RS virus, the lungs of the mice previously vaccinated with recombinants expressing F protein were free of detectable RS virus, whereas the lungs of unvaccinated mice contained 10(4.2) PFU of virus per g.

Cell-free translation of a chimeric eucaryotic-procaryotic message yields functional chloramphenicol acetyltransferase

A vaccinia virus (VV) recombinant containing the DNA sequences encoding the bacterial chloramphenicol acetyltransferase (CAT) gene was constructed. The ability of the chimeric VV:CAT transcript to be translated in vitro into enzymatically active enzyme was assessed. Addition of mRNA isolated from the cytoplasm of VV:CAT infected cells to a mRNA-dependent reticulocyte lysate resulted in the synthesis of high levels of enzymatically active CAT. These results suggest that this assay may be used in concert with physical assays to study the expression and stability of chimeric transcripts in virus-infected cells.

Identification and nucleotide sequence of the thymidine kinase gene of Shope fibroma virus

The thymidine kinase (TK) gene of Shope fibroma virus (SFV), a tumorigenic leporipoxvirus, was localized within the viral genome with degenerate oligonucleotide probes. These probes were constructed to two regions of high sequence conservation between the vaccinia virus TK gene and those of several known eucaryotic cellular TK genes, including human, mouse, hamster, and chicken TK genes. The oligonucleotide probes initially localized the SFV TK gene 50 kilobases (kb) from the right terminus of the 160-kb SFV genome within the 9.5-kb BamHI-HindIII fragment E. Fine-mapping analysis indicated that the TK gene was within a 1.2-kb AvaI-HaeIII fragment, and DNA sequencing of this region revealed an open reading frame capable of encoding a polypeptide of 176 amino acids possessing considerable homology to the TK genes of the vaccinia, variola, and monkeypox orthopoxviruses and also to a variety of cellular TK genes. Homology matrix analysis and homology scores suggest that the SFV TK gene has diverged significantly from its counterpart members in the orthopoxvirus genus. Nevertheless, the presence of conserved upstream open reading frames on the 5' side of all of the poxvirus TK genes indicates a similarity of functional organization between the orthopoxviruses and leporipoxviruses. These data suggest a common ancestral origin for at least some of the unique internal regions of the leporipoxviruses and orthopoxviruses as exemplified by SFV and vaccinia virus, respectively.

Hydroxyurea-resistant vaccinia virus: overproduction of ribonucleotide reductase

Repeated passages of vaccinia virus in increasing concentrations of hydroxyurea followed by plaque purification resulted in the isolation of variants capable of growth in 5 mM hydroxyurea, a drug concentration which inhibited the reproduction of wild-type vaccinia virus 1,000-fold. Analyses of viral protein synthesis by using [35S]methionine pulse-labeling at intervals throughout the infection cycle revealed that all isolates overproduced a 34,000-molecular-weight (MW) early polypeptide. Measurement of ribonucleoside-diphosphate reductase (EC 1.17.4.1) activity after infection indicated that 4- to 10-fold more activity was induced by hydroxyurea-resistant viruses than by the wild-type virus. A two-step partial purification which yielded greater than 90% of the induced ribonucleotide reductase activity in the fraction obtained by 35% saturation with ammonium sulfate resulted in a substantial enrichment for the 34,000-MW protein from extracts of wild-type and hydroxyurea-resistant-virus-infected, but not mock-infected, cells. In the presence of the drug, the isolates incorporated [3H]thymidine into DNA earlier and at a rate substantially greater than that of the wild type, although the onset of DNA synthesis was delayed in both cases. In the absence of the drug, the attainment of a maximum viral DNA synthesis rate was accelerated after infection by drug-resistant isolates. The drug resistance trait was markedly unstable in all isolates. In the absence of selective pressure, plaque-purified isolates readily segregated progeny that displayed a wide range of resistance phenotypes. The results of this study indicate that vaccinia virus encodes a subunit of ribonucleotide reductase which is a 34,000-MW early protein whose overproduction confers hydroxyurea resistance on reproducing viruses.

Human respiratory syncytial virus glycoprotein G expressed from a recombinant vaccinia virus vector protects mice against live-virus challenge

Recombinant vaccinia virus vectors were constructed which expressed the major surface glycoprotein G of human respiratory syncytial (RS) virus. The biological activity of the G protein expressed from these vectors was assayed. Inoculation of rabbits with live recombinant virus induced high titers of antibody which specifically immunoprecipitated RS virus G protein and was capable of neutralizing RS virus infectivity. Immunization of mice by either the intranasal or the intraperitoneal route with recombinant virus that expressed only the G protein resulted in complete protection of the lower respiratory tract upon subsequent challenge with live RS virus.

Regulation of protein synthesis in virus-infected animal cells

This chapter summarizes the structural features that govern the translation of viral mRNAs: where the synthesis of a protein starts and ends, how many proteins can be produced from one mRNA, and how efficiently. It focuses on the interplay between viral and cellular mRNAs and the translational machinery. That interplay, together with the intrinsic structure of viral mRNAs, determines the patterns of translation in infected cells. It also points out some possibilities for translational regulation that can only be glimpsed at present, but are likely to come into focus in the future. The mechanism of selecting the initiation site for protein synthesis appears to follow a single formula. The translational machinery displays a certain flexibility that is exploited more frequently by viral than by cellular mRNAs. Although some of the parameters that determine efficiency have been identified, how efficiently a given mRNA will be translated cannot be predicted by summing the known parameters.

Expression of the major glycoprotein G of human respiratory syncytial virus from recombinant vaccinia virus vectors

The major glycoprotein, G, of human respiratory syncytial (RS) virus is a Mr 84,000-90,000 species that has about 60% of its mass contributed by carbohydrate, most of which is in the form of O-linked oligosaccharides. The G protein contains neither a hydrophobic N-terminal signal sequence nor a hydrophobic C-terminal anchor region. Instead, its amino acid sequence reveals only one region with significant hydrophobic character, which is between residues 38 and 66. In order to study the synthesis, processing, and functions of this unusual viral glycoprotein, full-length cDNA copies of the G protein mRNA were inserted into the DNA genome of vaccinia virus (VV) in a position that was adjacent to a strong VV promoter and within the VV gene for thymidine kinase (TK). The resulting TK- recombinant viruses were selected, plaque-purified, and characterized by Southern blot analysis of restriction enzyme digests of the viral DNA. Recombinant RNA transcripts that contained both G-specific and VV-specific sequences accumulated in cells infected with recombinant viruses having the G protein gene in the positive orientation. The translation product of these transcripts in infected cells was a Mr 84,000-90,000 glycoprotein that was indistinguishable from authentic RS virus G protein. It could be detected in cell lysates after metabolic labeling with [3H]glucosamine and was immunoprecipitated by anti-RS-virus antiserum. Immunofluorescence studies showed that the G protein accumulated intracellularly with the perinuclear distribution that is characteristic of newly synthesized glycoproteins. Furthermore, the protein was also clearly detectable on the surface of recombinant-infected cells, showing that it was transported to and inserted into the plasma membrane.

Physical mapping and DNA sequence analysis of the rifampicin resistance locus in vaccinia virus

Rifampicin has been shown to inhibit the maturation of poxviruses at a discrete step in envelope formation (Moss et al., 1969; Pennington et al., 1970; Nagayama et al., 1970; Grimley et al., 1970). A rifampicin-resistant vaccinia virus mutant (RifR) was selected for its ability to grow in the presence of 100 micrograms/ml of rifampicin. Utilizing intact DNA or endonuclease restricted cloned DNA subfragments derived from the RifR mutant virus, the locus specifying rifampicin resistance was physically mapped by marker rescue analysis leftward of the unique XhoI site within the HindIII D fragment. DNA sequencing of a 445 bp fragment encompassing this region revealed an AT to GC transition when compared with the equivalent wild-type DNA fragment. Analysis of the six potential open reading frames within the 445-bp fragment indicated only one available open reading frame. On this basis, the rifampicin-resistant vaccinia virus mutant was shown to have a codon transition from asparagine to aspartic acid.

Expression and regulation of the vaccinia virus thymidine kinase gene in non-permissive cells

The expression and regulation of the vaccinia virus (VV) thymidine kinase (tk) gene was examined in two non-permissive cell lines, CHO and MDBK, which restrict VV development at different stages of the viral replication cycle. The VV tk gene was expressed in these two cell lines with kinetics similar to a fully permissive cell line BSC40. These results are consistent with the hypothesis that inhibition of tk mRNA translation by another viral early gene product is a normal component of the overall strategy employed to express and regulate the VV tk gene during a productive infection.

Vaccinia virus induces ribonucleotide reductase in primate cells

Infection of monkey kidney (BSC-40) cells with vaccinia virus strain WR resulted in a marked increase in ribonucleoside diphosphate reductase (EC 1.17.4.1) activity as measured by CDP reduction in cell-free extracts. After a synchronous infection, increased activity was detected at 2 h, peaked at 4 to 5 h, and then declined between 6 and 8 h to the endogenous cellular level. The induction, detectable at 0.5 PFU/cell, correlated strongly with multiplicity of infection to 10 PFU/cell and continued to increase to 50 PFU/cell. It paralleled the previously described induction of viral DNA polymerase and thymidine kinase, suggesting that the reductase may also be a product of early transcription of the viral genome. The inhibition of DNA synthesis throughout infection resulted in prolonged accumulation of reductase activity and delayed and incomplete down-regulation at 8 h, suggesting that repression involves late functions. Rescue of fluorodeoxyuridine-inhibited DNA synthesis with exogenous thymidine restored the normal pattern. Preferential association of the induced reductase with the cytoplasmic sites of vaccinia virus DNA replication (virosomes) was not detected. The induced enzyme is similar in several respects to other eucaryotic ribonucleotide reductases, but is distinct from host cell reductase in response to certain modulators of reductase activity (M. B. Slabaugh and Christopher K. Mathews, J. Virol. 52:501-506, 1984). Full activity required an activator, exogenous reducing equivalents, and iron. Hydroxyurea, EDTA, dATP, and dTTP inhibited CDP reduction, setting this reductase apart from T4 reductase, which is not inhibited by dATP, and from herpesvirus reductase, which requires no activation and is insensitive to deoxyribonucleoside triphosphate inhibition.

Identification of the DNA sequences encoding the large subunit of the mRNA-capping enzyme of vaccinia virus

The DNA sequences encoding the large subunit of the mRNA-capping enzyme of vaccinia virus were located on the viral genome. The formation of an enzyme-guanylate covalent intermediate labeled with [alpha-32P]GTP allowed the identification of the large subunit of the capping enzyme and was used to monitor the appearance of the enzyme during the infectious cycle. This assay confirmed that after vaccinia infection, a novel 84,000-molecular-weight polypeptide corresponding to the large subunit was rapidly synthesized before viral DNA replication. Hybrid-selected cell-free translation of early viral mRNA established that vaccinia virus encoded a polypeptide identical in molecular weight with the 32P-labeled 84,000-molecular-weight polypeptide found in vaccinia virions. Like the authentic capping enzyme, this virus-encoded cell-free translation product bound specifically to DNA-cellulose. A comparison of the partial proteolytic digestion fragments generated by V8 protease, chymotrypsin, and trypsin demonstrated that the 32P-labeled large subunit and the [35S]methionine-labeled cell-free translation product were identical. The mRNA encoding the large subunit of the capping enzyme was located 3.1 kilobase pairs to the left of the HindIII D restriction fragment of the vaccinia genome. Furthermore, the mRNA was determined to be 3.0 kilobases in size, and its 5' and 3' termini were precisely located by S1 nuclease analysis.

Indiscriminate degradation of RNAs in interferon-treated, vaccinia virus-infected mouse L cells

In this report we used Northern blot hybridization analysis to characterize the fate of several species of viral RNA transcribed from internal and terminal regions of vaccinia DNA in interferon-treated, infected mouse L cells grown in suspension. All species of viral RNAs were expressed but were reduced in amount. Larger-sized RNAs were reduced more than smaller-sized RNAs. This reduction appears to be related to the activation of the interferon-mediated double-stranded RNA-dependent 2-5A synthetase-endoribonuclease system, as the rRNA cleavage pattern characteristic of this system was observed early in infection and in cell extracts in response to exogenous 2-5A. Thus, in interferon-treated, vaccinia-infected mouse L cells in suspension, there is indiscriminate degradation of viral and cellular RNAs, and this RNA breakdown might play a role in the interferon-mediated inhibition of protein synthesis.

Nucleotide sequence of the thymidine kinase gene region of monkeypox and variola viruses

Among the orthopoxviruses variola virus induces in cells a characteristic thymidine kinase (TK) activity that can be feedback inhibited in reactions with thymidine triphosphate. Northern blot analyses of variola and monkeypox virus-infected cell extracts showed RNAs of the same molecular weight as the major (590-base) and minor (2380-base) TK transcripts described for vaccinia virus. The nucleotide sequences of 1275 bp in the TK gene region of variola and monkeypox viruses have been determined. When these sequences were compared with such sequences reported for vaccinia virus, differences were observed at 41 nucleotide positions. Examination of the putative encoded TK polypeptide for the three viruses revealed variation at eight amino acid positions. Two major differences in the amino acid composition of the variola virus TK were identified that might play a role in alteration of its kinetic properties.

Fine structure analysis and nucleotide sequence of the vaccinia virus thymidine kinase gene

The thymidine kinase (ATP:thymidine 5'-phosphotransferase, EC 2.7.1.21) gene of vaccinia virus has previously been mapped near the middle of the viral DNA, within the 4.85-kilobase HindIII J fragment, and shown to encode a Mr 19,000 polypeptide [Hruby, D. E. & Ball, L. A. (1982) J. Virol. 43, 403-409]. To locate the gene more precisely and to determine the structure of the basic transcriptional unit, the positions of cleavage sites for several restriction endonucleases were mapped within the HindIII J DNA fragment. Four appropriate subfragments of HindIII J DNA were inserted into plasmid pBR322 derivatives and cloned in Escherichia coli. These recombinant plasmid DNAs were tested for their ability to inhibit the cell-free synthesis of active thymidine kinase and to retain the mRNA for this enzyme when immobilized on nitrocellulose filters. The data showed that the gene spanned an EcoRI cleavage site that lies 850 base pairs from the left-hand end of the HindIII J fragment (the HindIII L-J boundary). Because hybridization of vaccinia virus DNA to partially purified thymidine kinase mRNA detected only a single 670-nucleotide RNA species capable of hybridizing to this region of the genome, nuclease S1 mapping experiments were carried out with thymidine kinase mRNA to protect DNA fragments that were terminally labeled at this EcoRI site. The results indicated that the gene extended from about 550 to 1,150 base pairs from the left end of HindIII J, was transcribed in a rightward direction, and contained no intervening sequences. Hence, a 1.04-kilobase Ava II-Hpa II restriction fragment containing this region of DNA was isolated and subjected to nucleotide sequence analysis. An examination of this nucleotide sequence revealed the presence of an open reading frame of 531 nucleotides capable of encoding a protein of 177 amino acids with a Mr of 20,077.

The white pock mutants of rabbit poxvirus: V. In vitro translation of early host range mutant mRNA

The abortive infections of pig kidney (PK) cells by both RP mu hr23 and RP mu hr31, two early (DNA minus) white pock (mu) host range (hr) mutants of rabbit poxvirus (RPV), are characterized by the in vivo inhibition of both host and viral protein synthesis by 10 hr postinfection although viral RNA synthesis continues. Further analysis reveals that large quantities of functional viral mRNA can be isolated from PK cells abortively infected with RP mu hr23 and translated in vitro throughout the 10-hr period of infection, even though these mRNAs are almost totally inactive in vivo. The in vitro translation of accumulated mRNA isolated from PK cells abortively infected by RP mu hr31 shows a quite different pattern where the maximum amount of RNA translatable in vitro is found at 6 hr postinfection with lesser amounts at 10 hr postinfection. Although early or prereplicative viral proteins are detected with each mutant both in vivo and after in vitro translation of isolated RNA, few, if any, late proteins are observed under any conditions.