Purified influenza virus nucleoprotein protects mice from lethal infection

Local administration of nucleoprotein purified from X31 (H3N2) influenza A virus primed for A virus cross-reactive cytotoxic T cells and resulted in substantial protection (75%) of mice from a lethal challenge with the heterologous mouse-adapted A/PR/8/34 (H1N1) virus. By following the course of a lethal virus challenge we found that nucleoprotein priming did not prevent virus infection but rather aided recovery. Nucleoprotein-primed mice suffered initial symptoms of infection, i.e. weight loss and surface temperature changes, but started to recover after approximately 7 days. We suggest that such heterotypic protection can be attributed to priming of A virus cross-reactive cytotoxic T cells.

The roles of influenza virus haemagglutinin and nucleoprotein in protection: analysis using vaccinia virus recombinants

Vaccinia virus recombinants expressing haemagglutinin (HA) or nucleoprotein (NP) from influenza virus A/PR/8/34 were used to investigate protective immunity in mice, with two protocols. Protection was assessed by mortality and morbidity rates and by lung virus titres after infection intranasally with A/PR/8/34. In the first protocol, mice immunized with vaccinia-HA recombinant virus and infected intranasally with A/PR/8/34 were almost totally protected, but mice immunized with vaccinia-NP virus were very poorly protected. In the second protocol, the recombinant viruses were used to stimulate in vitro T cells that are specific for HA and NP; both populations of T cells, when transferred to A/PR/8/34-infected mice, afforded good protection. The results indicate that an immune response specific for just HA provided protection that was almost indistinguishable from that provided by whole A/PR/8/34. On the other hand, immunization with vaccinia-NP provided poor protective immunity, despite the fact that transferred NP-specific T cells were very effective and vaccinia-NP immunization has previously been shown to stimulate cytotoxic T cells. These results demonstrate that a single viral antigen, delivered by live vaccinia virus, can provide effective protection, but that immunization for cross-protection against heterologous influenza virus remains elusive.

The genome-linked proteins of aphthoviruses: specific immunoprecipitation of the three species detected on virus RNA and identification of possible precursors

Synthetic peptides have been made corresponding to the C-terminal portion of each of the three presumptive genome-linked proteins (VPgs) of foot-and-mouth disease virus type A10. Antisera against each of these peptides efficiently precipitated only the homologous VPg, and the reactions were inhibited by prior absorption with homologous, but not heterologous synthetic peptide. The peptide antisera precipitated a number of proteins from infected cell extracts with mol. wt. of 100, 84, 56, 36, 27, 25 and 20, all X 10(3); all these reactions were inhibited by absorption with homologous peptide, indicating that they were probable precursors of VPg. The relationship between these proteins is at present unclear.

Initiation of poliovirus plus-strand RNA synthesis in a membrane complex of infected HeLa cells

An in vitro poliovirus RNA-synthesizing system derived from a crude membrane fraction of infected HeLa cells was used to analyze the mechanism of initiation of poliovirus plus-strand RNA synthesis. This system contains an activity that synthesizes the nucleotidyl proteins VPg-pU and VPg-pUpU. These molecules represent the 5'-terminal structure of nascent RNA molecules and of virion RNA. The membranous replication complex is also capable of synthesizing nucleotidyl proteins containing nine or more of the poliovirus 5'-proximal nucleotides as assayed by the formation of the RNase T1-resistant oligonucleotide VPg-pUUAAAACAGp or by fingerprint analysis of the in vitro-synthesized RNA. Incubation of preformed VPg-pUpU with unlabeled nucleoside triphosphates resulted in the formation of VPg-pUUAAAACAGp. This reaction, which appeared to be an elongation of VPg-pUpU, was stimulated by the addition of a soluble fraction (S-10) obtained from uninfected HeLa cells. Preformed VPg-pU could be chased into VPg-pUpU in the presence of UTP. Our data are consistent with a model that VPg-pU can function as a primer for poliovirus plus-strand RNA synthesis in the membranous replication complex and that the elongation reaction may be stimulated by a host cellular factor.

Detection of a genome-linked protein (VPg) of hepatitis A virus and its comparison with other picornaviral VPgs

The nucleotide sequence corresponding to the P3 region of the hepatitis A virus (HAV) polyprotein genome was determined from cloned cDNA and translated into an amino acid sequence. Comparison of the amino acid sequences of the genome-linked proteins (VPgs) of other picornaviruses with the predicted amino acid sequence of HAV was used to locate the primary structure of a putative VPg within the genome of HAV. The sequence of HAV VPg, like those of other picornaviral VPg molecules, contains a tyrosine residue as a potential binding site for HAV RNA in position 3 from its N terminus. The potential cleavage sites to generate VPg from a putative HAV polyprotein are between glutamic acid and glycine at the N terminus and glutamic acid and serine or glutamine and serine at the C terminus. A synthetic peptide corresponding to 10 amino acids of the predicted C terminus of HAV VPg induced anti-peptide antibodies in rabbits when it was conjugated to thyroglobulin as a carrier. These antibodies were specific for the peptide and precipitated VPg, linked to HAV RNA, from purified HAV and from lysates of HAV-infected cells. The precipitation reaction was blocked by the synthetic peptide (free in solution or coupled to carrier proteins) and prevented by pretreatment of VPg RNA with protease. Thus, our predicted amino acid sequence is colinear with the nucleotide sequence of the VPg gene in the HAV genome. From our results we concluded that HAV has the typical organization of picornavirus genes in this part of its genome. Similarity among hydrophobicity patterns of amino acid sequences of different picornaviral VPgs was revealed in hydropathy plots. Thus, the VPg of HAV appears to be closely related to VPg1 and VPg2 of foot-and-mouth disease virus. In contrast, HAV VPg has a unique isoelectric point (pI = 7.15) among the picornavirus VPgs.

Anti-VPg antibody precipitation of product RNA synthesized in vitro by the poliovirus polymerase and host factor is mediated by VPg on the poliovirion RNA template

Antibody to the poliovirus genome-linked protein, VPg, specifically immunoprecipitated the product RNA synthesized in vitro by the poliovirus RNA polymerase and HeLa cell host factor when VPg-linked poliovirion RNA was used as a template. The largest product RNA that was immunoprecipitated was twice the size of the template RNA. The complete denaturation of the product RNA with CH3HgOH had no effect on the immunoprecipitation reaction. In contrast, CH3HgOH denaturation prevented the immunoprecipitation of the oligo(U)-primed product RNA. Immunoprecipitation of the product RNA synthesized in the host-factor-dependent reaction was prevented if VPg was removed from the template RNA by pretreatment with proteinase K or if an RNA template without VPg was used in the reaction. The results support our previous evidence that a covalent linkage exists between the labeled negative-strand product RNA and the VPg-linked template RNA and suggest that the purified polymerase and host factor initiated RNA synthesis in vitro in the absence of VPg or a VPg-precursor protein.

Synthesis of plus- and minus-strand RNA from poliovirion RNA template in vitro

The poliovirus RNA polymerase, 3Dpol, was used to synthesize RNA in vitro in the presence of a host factor preparation from uninfected HeLa cells and poliovirion RNA as the template. The transcription products included molecules approximately twice the length of the template, apparently resulting from hairpin formation and template-directed elongation, as previously reported (D. C. Young, D. M. Tuschall, and J. B. Flanegan, J. Virol. 54:256-264, 1985). Other polyadenylated template RNAs also yielded products that were twice the length of the template. The polarity of the products synthesized from plus-strand poliovirus RNA template was analyzed by Southern blotting using labeled product RNA to probe single-stranded poliovirus DNAs cloned into M13 vectors. The results demonstrated that host factor-mediated polymerase products contain newly synthesized plus-strand sequences as well as the expected minus-strand sequences. Polymerase products primed with oligo(U) were all of minus-strand polarity.

Low responder MHC alleles for Tc recognition of influenza nucleoprotein

Since virus nucleoprotein is an important target antigen for anti-influenza cytotoxic T cells (Tc), we examined the genetics of Tc responses to this single viral protein to find three nonresponder alleles (Dd, Dk, and Kb) in three haplotypes and their recombinants so far tested. B10.A(5R) mice bearing nonresponder MHC class I antigen in the D and K regions show no anti-NP Tc responses, however they do show a strong A-virus cross-reactive anti-influenza cytotoxicity. The high frequency of nonresponsiveness to a single viral component, as compared with the entire virus, has implications for the development of simple vaccines.

Molecular cloning and sequence determination of the genomic regions encoding protease and genome-linked protein of three picornaviruses

To investigate the degree of similarity between picornavirus proteases, we cloned the genomic cDNAs of an enterovirus, echovirus 9 (strain Barty), and two rhinoviruses, serotypes 1A and 14LP, and determined the nucleotide sequence of the region which, by analogy to poliovirus, encodes the protease. The nucleotide sequence of the region encoding the genome-linked protein VPg, immediately adjacent to the protease, was also determined. Comparison of nucleotide and deduced amino acid sequences with other available picornavirus sequences showed remarkable homology in proteases and among VPgs. Three highly conserved peptide regions were identified in the protease; one of these is specific for human picornaviruses and has no obvious counterpart in encephalomyocarditis virus, foot-and-mouth disease virus, or cowpea mosaic virus proteases. Within the other two peptide regions two conserved amino acids, Cys 147 and His 161, could be the reactive residues of the active site. We used a statistical method to predict certain features of the secondary structures, such as alpha helices, beta sheets, and turns, and found many of these conformations to be conserved. The hydropathy profiles of the compared proteases were also strikingly similar. Thus, the proteases of human picornaviruses very probably have a similar three-dimensional structure.

Hexavalent capsomers of herpes simplex virus type 2: symmetry, shape, dimensions, and oligomeric status

The structures of the hexavalent capsomers of herpes simplex virus type 2 were analyzed by negative staining electron microscopy of capsomer patches derived from partially disrupted nucleocapsids. Optimally computer-averaged images were formed for each of the three classes of capsomer distinguished by their respective positions on the surface of the icosahedral capsid with a triangulation number of 16; in projection, each capsomer exhibited unequivocal sixfold symmetry. According to correspondence analysis of our set of capsomer images, no significant structural differences were detected among the three classes of capsomers, as visualized under these conditions. Taking into account information from images of freeze-dried, platinum-shadowed nucleocapsid fragments, it was established that each hexavalent capsomer is a hexamer of the 155-kilodalton major capsid protein. The capsomer has the form of a sixfold hollow cone approximately 12 nm in diameter and approximately 15 nm in depth, whose axial channel tapers in width from the outside towards the inner capsid surface.

[Characteristics of an enzyme hydrolyzing the covalent bond between RNA and protein VPg of the encephalomyocarditis virus]

The enzyme termed by us as uridilylpolynucleotide-(5'P----O)-tyrosine phosphodiesterase (Y-pUpN PDE) was isolated from mouse ascites Krebs II cells by ion-exchange and affinity chromatography. The enzyme was found to specifically split the natural covalent bond between VPg and EMC or polio viral RNAs. The enzyme is completely inactivated at 55 degrees C and partially by EDTA. The enzyme preparation isolated by the above-mentioned procedure is not homogeneous and contains inhibiting admixture(s). Possible role of the enzyme in living cells is discussed.

Expression of Sendai virus defective-interfering genomes with internal deletions

Sendai virus strain 7 has been shown to contain four defective interfering (DI) RNA species in which both genome termini and various adjacent fragments of the 3'-terminal NP gene and 5'-terminal L gene are represented, but most or all internal genes and gene boundaries are deleted. Previous sequence analyses of these mutant RNAs suggested that all four possessed the transcription initiation signal of the NP gene and the transcription termination signal of the L gene. The supposition that these signals should specify transcripts has now been supported by oligo(dT) selection of four DI 7 specific RNA species that had apparent molecular weights slightly lower than each DI genome. DI RNA 7a, which contains the entire NP gene, except for two U residues at the end of the poly(A) initiation signal, appeared to be transcribed solely as a readthrough product. Since DI RNA 7a contains the entire NP protein-coding sequence and DI RNAs 7c and 7d contain fragments of it, whereas DI RNA 7b is devoid of it, only transcripts of RNAs 7c and 7d were expected to specify fusion proteins containing NP gene-specific sequences. A strain 7-induced protein that reacted with monoclonal antibodies against the NP protein had the 33,000 Mr size appropriate for the translation product predicted by the sequence of RNA 7d. Other proteins of lower molecular weight were seen only in cells infected by strain 7, but they did not react with NP-specific antibody and their translation in vitro was not blocked by hybridization to an NP gene-specific oligonucleotide. Therefore, at least some of these proteins may be cellular products induced by DI virus infection. These DI transcripts and translation products may influence interference with replication of the parental helper virus.

Nucleotide sequences responsible for generation of internally deleted Sendai virus defective interfering genomes

The deletion points of four internally deleted defective interfering (DI) RNA species (7a, 7b, 7c, and 7d) that reside in a single Sendai virus strain were defined by nucleotide sequencing. DI RNA 7a (Mr 1.24 x 10(6)) retained the entire NP gene with the complete NP protein-coding sequence, except for the last two U residues of the polyadenylation signal, fused to an 1800-nucleotide sequence comprising 5'-terminal genome and adjacent L gene sequences. DI RNA 7b (Mr, 0.70 x 10(6)) consisted of 100 3'-terminal nucleotides fused to 1900 5'-terminal bases; the deletion point in the NP gene precedes the NP protein initiation codon. DI RNA 7c (Mr 0.55 x 10(6)) retained 420 3'-terminal and 1150 5'-terminal nucleotides. The sequence just downstream of the sequenced deletion site is M gene specific, indicating that 7c arose from at least two deletion events and that it comprises NP, M, and L gene fragments. Transcription of RNA 7c could yield an MRNA encoding a fusion protein with a 14,000 Mr (N-terminal NP sequence fused to out of frame M-specific amino acids). DI RNA 7d (Mr 0.92 x 10(6)) retained 1027 3'-terminal nucleotides fused to 1600 bases from the 5'-terminus. It has an open reading frame for a 33,000 Mr N-terminal NP protein fragment. Nucleotide sequences flanking each deletion and just downstream of the NP gene deletion site suggested that these DI genomes were generated by a copy-choice mechanism, involving polymerase jumping during replication of negative polarity virus genome templates. In this process, the termination and reinitiation of RNA synthesis would involve recognition of sequences that regulate virus genome transcription and replication.

Monoclonal antibodies to murine retrovirus protein p30

Hybrid cell lines were prepared by the fusion of mouse myeloma cells with the spleen cells of Wistar-Furth rats that had been immunized with a Moloney sarcoma virus (Mo-MuSV)-induced tumour, MFU. Two immunization protocols were designed. In the first, the animals received several injections of irradiated (10 000 rad) cells of a tumour cell line established in vitro, MFU-67. The rats received a booster injection 3 days prior to fusion. In the second protocol, immunization was the result of simple tumour growth, and no booster was given. Hybrids were tested by immunofluorescence for the production of immunoglobulins reacting with mouse cells acutely infected with Mo-MuSV. Over 20% of reactive hybrids were observed in the tumour growth protocol, and about 10% in the irradiated cell protocol when the last injection of the series was given 2 weeks before fusion. After 6 months, the proportion fell to 3%. Hybrid lines producing antibody to p30, the major core polypeptide of murine retroviruses, were obtained by cloning. Three of these were selected for closer study and were found to recognize three non-overlapping epitopes on p30. By direct and competitive binding in ELISA tests, the three epitopes were found to have very different distribution patterns among the various strains and isolates of murine retroviruses.

Sequence analysis of the viral core protein and the membrane-associated proteins V1 and NV2 of the flavivirus West Nile virus and of the genome sequence for these proteins

Cell-associated flaviviruses contain the two membrane proteins V3 and NV2 besides the viral core protein V2 whereas extracellular viruses do contain V2 protein and the two membrane proteins V3 and V1. Since the V1 protein could not be detected in infected cells it has been suggested that V1 is generated from NV2 by proteolytic cleavage during the release of virus from cells (D. Shapiro, W. E. Brandt, and P. K. Russell (1972), Virology 50, 906-911). We have isolated the viral structural proteins V1, V2, and NV2 from the flavivirus West Nile virus and determined their amino-terminal amino acid sequences and amino acid sequences of peptides derived from these proteins. We have also transcribed parts of the viral genome into cDNA and cloned and sequenced this cDNA. The analyses of the protein structure of V1, V2, and NV2 together with the determination of the amino-terminal sequence of V3 (data not shown) have allowed us to identify the nucleotide region coding for the structural proteins V2, NV2, and V1. The primary structure of this nucleotide sequence is presented in this report. The data show that the amino terminus of the viral core protein V2 is followed by the amino termini of the proteins NV2, V1, and V3, respectively. These data for the first time identify the exact order of all structural proteins of a flavivirus identified so far. Our data strongly support the above-mentioned hypothesis that V1 is derived from NV2 by proteolytic cleavage and furthermore indicate that V1 represents the nonglycosylated carboxy-terminal part of NV2 which contains those sequences which anchor NV2 in the viral membrane. A working hypothesis is presented in which two species of cellular enzymes, signalase(s) removing signal sequences and enzymes involved in cleaving polyproteins after a pair of basic amino acids, do generate the proteins V2, NV2, and V1 from the growing peptide chain synthesized during translation of the 42 S genome RNA which functions as mRNA for these proteins.

Abrogation of cell surface expression of human class I transplantation antigens by an adenovirus protein in Xenopus laevis oocytes

Class I transplantation antigens form complexes with a virus protein encoded in the early region E3 of the adenovirus-2 genome. The interaction between this viral glycoprotein, E19, and nascent human class I antigens has been examined by microinjecting purified mRNA into Xenopus laevis oocytes. Both E19 and the two class I antigen subunits, the heavy chain and beta 2-microglobulin (beta 2M), were efficiently translated. The heavy chains did not become terminally glycosylated, as monitored by endoglycosidase H digestion, and were not expressed on the oocyte surface unless they were associated with beta 2M. The E19 protein did not become terminally glycosylated, and we failed to detect this viral protein on the surface of the oocytes. Co-translation of heavy chain and E19 mRNA demonstrated that the two proteins associate intracellularly. However, neither protein appeared to be transported to the trans-Golgi compartment. Similar observations were made in adenovirus-infected HeLa cells. Heavy chains bound to beta 2M became terminally glycosylated in oocytes in the presence of low concentrations of E19. At high concentrations of the viral protein, no carbohydrate modifications and no cell surface expression of class I antigens were apparent. Thus, beta 2M and E19 have opposite effects on the intracellular transport of the heavy chains. These data suggest that adenovirus-2 may impede the cell surface expression of class I antigens to escape immune surveillance.

Interactions among the three adenovirus core proteins

Interactions among the three adenovirus core polypeptides V, VII, and mu were examined, using the reversible chemical cross-linker dithiobis(succinimidyl propionate) and two-dimensional polyacrylamide gel electrophoresis. Cross-linked species obtained from gradient-purified adenovirus type 2 cores were well represented among the cross-linked products of pentonless virions and crude core preparations. The more efficiently formed cross-linked core species were also identified with the arginine-specific cross-linker, p-azidophenyl glyoxal. In addition to dimers of polypeptides V and VII, efficient cross-linking of V to VII, V to mu, and VII to V to mu was detected in adenovirus cores. Notably absent were cross-linked species corresponding to higher multimers of polypeptide VII. A major core-capsid interaction appeared to be via the association of polypeptide V with a dimer of polypeptide VI.

Characterization of major structural proteins of measles virus with monoclonal antibodies

We have prepared and characterized monoclonal antibodies against five major structural proteins, i.e. the HA, P, NP, F and M proteins, of measles virus. At least three non-overlapping antigenic sites were delineated on the HA protein, three on the P, four on the NP, four on the F and five on the M proteins by competitive binding assays. Antigenic sites on the HA and F proteins roughly represented functional domains defined by serological tests. The reactivity of monoclonal antibodies with various measles virus strains including those from subacute sclerosing panencephalitis (SSPE) and other members of the morbillivirus family was studied by immunofluorescence. A monoclonal antibody or set of monoclonal antibodies to each of the antigenic sites showed a characteristic pattern of cross-reactivity with heterologous strains. The HA and NP proteins were antigenically the most variable, followed by the F and M proteins, while the P protein was relatively stable. None of the 14 anti-M monoclonal antibodies reacted with non-virus-producing SSPE cells, strongly suggesting the absence of M protein in these cells.

Antigenic cross-reactivity between caprine arthritis-encephalitis, visna and progressive pneumonia viruses involves all virion-associated proteins and glycoproteins

Antigenic relatedness between the virion-associated proteins of caprine arthritis-encephalitis, visna and progressive pneumonia viruses was examined. Antigenic cross-reactivity was assessed by immunoprecipitation of disrupted, radiolabelled virus with goat, sheep and rabbit antisera, followed by resolution of the immunoprecipitation products by SDS-polyacrylamide gel electrophoresis. The results indicate that antigenic cross-reactivity between the caprine and ovine virus isolates involves all of the major virion-associated proteins and glycoproteins. The common antigenic determinants exhibited by virion structural proteins are immunogenic in goats, sheep and rabbits.

[Synthesis, cloning and determination of the primary structure of a full-size DNA copy of the NP protein gene from influenza virus type A]

Complete nucleotide sequence of the cloned full-length DNA copy of the influenza virus A (H1N1) RNA segment 5 has been determined. The degree of nucleotide difference between two variants of A/PR/8/34 strain is estimated. The possible secondary structure of the segment 5 is deduced from the nucleotide sequence of some clones.

Hybridoma antibodies produced against bromelain derived cores of influenza virus

Splenic lymphocytes from BALB/c mice immunized with "cores" of influenza virus, obtained after bromelain cleavage of the surface glycoprotein, were fused with the P3-NS1/1-Ag-1 mouse cell line to yield hybridoma cultures. Among 20 stable cloned hybrid cells secreting monoclonal antibodies, one was specific for the nucleoprotein (NP), 11 were specific for the membrane (M) protein and eight were specific for the hemagglutinin (HA). These "cores" used as immunogen contained only the internal proteins of the influenza virus, namely the three polymerases, the NP and the M protein and no HA when examined by standard procedures of SDS-PAGE, electron microscopy and hemagglutination activity. It thus appeared that a small amount of contaminating antigens can sensitize a sufficient number of mouse B cells to be selected as hybrid partners. These antibodies were provisionally assigned as anti-carbohydrate attached to the HA.

Murine TH response to influenza virus: recognition of hemagglutinin, neuraminidase, matrix, and nucleoproteins

BALB/c mice were primed with type A influenza virus by footpad injection or by aerosol infection with PR8 [A/PR/8/34-(H1N1)]. Isolated T cells from draining lymph nodes were then tested for their proliferation in the presence of purified viral proteins hemagglutinin, neuraminidase, matrix, and nucleoprotein. Significant responses [( 3H]thymidine incorporation) were seen against each of the four proteins after either priming scheme. When helper T (TH) cell clones were isolated by hybridoma formation from two different strains of mice, responsiveness (interleukin 2 production) towards each protein was against apparent. Of 12 virus-specific T cell hybridomas isolated, four responded to matrix, three to nucleoprotein, one to neuraminidase, three to hemagglutinin, and one cell was of undefined specificity. Each hybridoma was also tested for recognition of the HK virus [A/Hong Kong/1/68-(H3N2)], which differs in subtype from the priming strain. All matrix-specific cells, two nucleoprotein-specific cells, and the cell of undefined specificity were cross-reactive with HK virus. H1-subtype specificity was seen for all hemagglutinin and neuraminidase-specific cells and one of the three nucleoprotein-specific cells. Because many virus-immune TH cells recognize antigenically variable determinants, a significant fraction of TH cell function may be lost after virus evolution. When selecting priming schemes for long-term immunization against influenza, the isolated enhancement of TH cells recognizing conserved determinants on matrix and nucleoprotein may therefore be considered.