Respiratory syncytial virus proteins: identification by immunoprecipitation

Chapter 8 Paramyxoviruses

The paramyxoviruses are a heterogeneous group of viruses causing a variety of clinical diseases in humans, animals, and birds. This chapter examines in more detail the structure and properties of the important human viruses in this group, namely measles, respiratory syncytial virus (RSV), mumps and parainfluenza viruses I-V. They are all enveloped, negative-stranded, riboviruses of helical symmetry. It is suggested that susceptible children, adolescents, and adults should be vaccinated against mumps, unless vaccination is contraindicated. Mumps vaccine can be of particular value to children approaching puberty and for adolescents and adults, especially males who have not had mumps in childhood. Ribavirin therapy may be particularly beneficial for children at risk for severe and often fatal RSV infection, such as infants with congenital heart disease. Attenuated measles vaccines have been developed empirically by selection of host range mutants, and are widely and successfully used throughout the world. Using the vaccine, some countries may soon eliminate measles as an endogenous virus but continued problems are anticipated, particularly in adults with viruses re-introduced by visitors from abroad. Basic studies on new antivirals are continuing (particularly with oligopeptides) but antiviral compounds are unlikely to have extended use in the clinic, except perhaps in tropical areas where the disease may be life threatening. However, a vaccination programme in these areas is preferable, and is an urgent need.

Neutralization of respiratory syncytial virus after cell attachment

Little is known about the mechanisms of antibody-mediated neutralization of respiratory syncytial virus (RSV) which causes recurrent infections in human despite the virtually universal presence of neutralizing serum antibodies. Human serum neutralization titers showed strong correlation with post-cell-attachment neutralizing titers for both RSV-convalescent sera and control sera but showed less strong correlation with cell-attachment blocking titers. Neutralization was effective for the first 60 min of infection, indicating that immune serum-mediated neutralization of RSV infection largely involves inhibition of early events following cell attachment.

Antibody-dependent enhancement of respiratory syncytial virus infection by sera from young infants

Respiratory syncytial virus (RSV) convalescent-phase sera and control sera from both infants ( < 6 months) and older individuals (1.5 to 90 years) were assayed for RSV-specific antibodies by neutralization, in vitro enhancing activity, and immunoprecipitation. Enhancement of RSV infection in U937 cells was demonstrated with convalescent-phase sera and was shown to be dependent on Fc receptors by blocking with human immunoglobulin G (P < 0.01). Convalescent-phase sera from infants enhanced infection at concentrations closer to physiological ones (10(-1) to 10(-3) dilutions of serum), while convalescent-phase sera from older individuals enhanced infection only at much lower concentrations (10(-3) to 10(-6) dilutions of serum; P < 0.01). To our knowledge, this is the first report of RSV-enhancing antibody activity in the sera of infants. The observed enhancing activity and the low neutralizing antibody levels are confined mostly to convalescent-phase sera from infants aged 0 to 6 months, suggesting that these factors may contribute to the increased severity of RSV disease frequently encountered in young infants.

Evidence for sense RNA-mediated protection to PVYN in tobacco plants transformed with the viral coat protein cistron

The coat protein (CP) cistron of the tobacco veinal necrosis strain of potato virus Y (PVYN), supplemented with translational start signals, was cloned into an Agrobacterium tumefaciens Ti transformation vector. Transformation of tobacco leaf discs resulted in 99 transgenic lines which were subsequently analysed for the presence and expression, at both the transcriptional and translational level, of the CP-gene. Although CP-specific RNA transcripts were produced in all plants no CP could be detected by several sensitive immunological techniques. Upon mechanical inoculation of progeny lines of self-pollinated original transformants (S1) with PVYN, protection levels of 20 and 95%, respectively, could be observed in two out of ten lines tested. This level of protection increased to 100% in the S2 progeny obtained from self-pollination of virus-protected S1 plants. Transformation of tobacco leaf discs with a PVYN CP construct from which the ATG start codon had been removed by site-directed mutagenesis resulted in 57 transgenic lines that all produced CP-specific transcripts. Mechanical inoculation with PVYN of S1 progeny plants of several of these lines resulted in resistance to a similar level and extent as in the S1 progeny of plants transformed with the intact CP cistron. The results obtained strongly suggest that the resistance observed in the transgenic plants is principally based on the presence of PVYN CP RNA sequences rather than on the accumulation of viral coat protein.

Active respiratory syncytial virus purified by ion-exchange chromatography: characterization of binding and elution requirements

Two viruses, respiratory syncytial virus (RSV) and vesicular stomatitis virus (VSV) were used to evaluate viral purification by an affinity resin column (Matrex Cellufine Sulfate (MCS); Amicon Division, WR Grace & Co.). Viable RSV was purified significantly from crude cell lysate by a single pass through a column containing the anionic MCS resin. Most cell protein and albumin eluted from the MCS resin with phosphate buffered saline (PBS) but RSV eluted at high ionic strength, i.e., greater than or equal to 0.6 M NaCl. Further purification was possible by sucrose step gradient centrifugation. The RSV prepared by column purification or by column plus sucrose gradient separation was both intact and infective. RSV and pure samples of VSV were used to optimize ionic strength and salts for elution from the MCS column: 0.8 M NaCl removed most of the viral protein. The capacity of the MCS gel for RSV or VSV was found to be about 0.6-0.8 mg viral protein per ml of hydrated resin. Detergent-solubilized viral membrane proteins bound to the MCS resin in 0.145 M NaCl and eluted with higher salt concentrations. Thus, this resin also may be a useful aid for relatively gentle purification of these proteins.

Distinguishing between respiratory syncytial virus subgroups by protein profile analysis

We subgrouped 75 strains of respiratory syncytial virus by a protein profile method (PPM) which relies on different mobilities of the phosphoprotein in one-dimensional polyacrylamide gel electrophoresis and does not require monoclonal antibodies. When compared with enzyme immunoassay, PPM correctly subgrouped 54 of 56 subgroup A and all 19 subgroup B strains.

Characterization of an in vitro system for the synthesis of mRNA from human parainfluenza virus type 3

A cell extract derived from human parainfluenza virus type 3-infected human lung carcinoma (HLC) cells synthesized mRNA in vitro. Under optimal conditions, the extract was able to support transcription of all virus-encoded genes as determined by hybridization analyses. The RNA products contained full-length poly(A)-containing mRNA species similar to those observed in acutely infected cells. Further purification of the viral nucleocapsids from the infected HLC cell extract resulted in total loss of the capacity of the extract to synthesize mRNA in vitro. However, the addition of cytoplasmic extracts from uninfected HLC cells to the nucleocapsid preparations restored transcription to levels observed in the infected cell lysates, indicating requirement of a host factor(s) in the human parainfluenza virus type 3 transcription process. In distinction to the abundant transcription observed in the cell extract from HLC cells, cell extract prepared from CV-1 cells failed to support transcription in vitro. High levels of RNase activity in the cell extract from CV-1 cells appears to be the principal reason for this difference.

Comparison of caprine, human and bovine strains of respiratory syncytial virus

A new continuous ovine kidney cell line allowing the growth of caprine, human and bovine respiratory syncytial virus was used to minimize host cell related variations for the direct comparison of the viral ultrastructures, serological relationships and structural protein profiles. Results show that all three strains are closely related although a closer relationship was found between bovine and caprine RS.

Comparative sensitivity of 125I-protein A and enzyme-conjugated antibodies for detection of immunoblotted proteins

Immunoblotting is a powerful technique for the detection of small amounts of immunologically interesting proteins in unpurified preparations. Iodinated protein A (PA) has been widely used as a second antibody for detection of proteins; however, it does not bind equally well to immunoglobulins from different species nor does it bind to all subclasses of immunoglobulin G (IgG). We compared the sensitivity of [125I]PA with those of both horseradish peroxidase-conjugated second antibodies (HRP) and glucose oxidase-anti-glucose oxidase (GAG) soluble complexes for visualizing bovine serum albumin, human IgG, or human C3 which was either dot blotted or electroblotted to nitrocellulose. [125I]PA was uniformly 10- to 100-fold less sensitive than either HRP or GAG. GAG was more sensitive than HRP except for C3 (electroblotting) and bovine serum albumin and IgG (dot blotting), in which they were equivalent. In general, dot blotting was 10- to 1,000-fold more sensitive than electroblotting. Although relative sensitivities varied depending on the proteins analyzed and the antisera used, GAG appeared to be superior to [125I]PA and HRP for detection of immunoblotted proteins.

Respiratory syncytial virus envelope glycoprotein (G) has a novel structure

Amino acid sequence of human respiratory syncytial virus envelope glycoprotein (G) was deduced from the DNA sequence of a recombinant plasmid and confirmed by limited amino acid microsequencing of purified 90K G protein. The calculated molecular mass of the protein encoded by the only long open reading frame of 298 amino acids was 32,588 daltons and was somewhat smaller than the 36K polypeptide translated in vitro from mRNA selected by this plasmid. Inspection of the sequence revealed a single hydrophobic domain of 23 amino acids capable of membrane insertion at 41 residues from the N-terminus. There was no N-terminal signal sequence and the hydrophilic N-terminal 20 residues probably represent the cytoplasmic tail of the protein. The N-terminally oriented membrane insertion was somewhat analogous to paramyxovirus hemagglutinin-neuraminidase (HN) and influenza neuraminidase (NA). The protein was moderately hydrophilic and rich in hydroxy-amino acids. It was both N- and O-glycosylated with the latter contributing significantly to the net molecular mass 90K.

mRNA sequence of three respiratory syncytial virus genes encoding two nonstructural proteins and a 22K structural protein

An mRNA sequence of two human respiratory syncytial viral nonstructural protein genes and of a gene for a 22,000-molecular-weight (22K) protein was obtained by cDNA cloning and DNA sequencing. Sequences corresponding to the 5' ends of the respective transcripts were deduced directly by primer extension and dideoxy nucleotide sequencing of the mRNAs. The availability of a bicistronic clone (pRSC6) confirmed the gene order for this portion of the genome. Contrary to other unsegmented negative-stranded RNA viruses, a 19-nucleotide intercistronic sequence was present between the NS1 and NS2 genes. The translation of cloned viral sequences in the bicistronic and monocistronic clones (pRSNS1 and pRSNS2) revealed two moderately hydrophobic proteins of 15,568 and 14,703 daltons. Their similarity in molecular size explained our earlier inability to resolve these proteins. A DNA sequence of an additional recombinant plasmid (pRSA2) revealed a long open reading frame encoding a 22,156-dalton protein containing 194 amino acids. It was relatively basic and moderately hydrophobic. A protein of this size was readily translated in vitro from a viral mRNA hybrid selected by this plasmid and corresponded to an unglycosylated 22K protein seen in purified extracellular virus but not associated with detergent- and salt-resistant cores. A second open reading frame of 90 amino acids partially overlapping with the C terminus of the 22K protein was also present within this sequence. This was reminiscent of the viral matrix protein gene which was previously shown by us to contain two overlapping reading frames. The finding of three additional viral transcripts encoding at least three identifiable proteins in human respiratory syncytial virus was a novel departure from the usual genetic organization of paramyxoviruses. The 5' ends of all three transcripts had a 5'NGGGCAAAU sequence that is common to all viral transcripts analyzed so far. Although there was no obvious homology immediately upstream of the polyadenylate tail, an AGUUA (AGUAA in the case of NS2) was present between 1 and 4 nucleotides upstream of the polyadenylate end of NS1 and 22K protein mRNAs.

Studies on human parainfluenza virus 3: characterization of the structural proteins and in vitro synthesized proteins coded by mRNAs isolated from infected cells

The structural proteins of human parainfluenza virus 3, a member of the paramyxovirus family, were characterized by SDS-polyacrylamide gel electrophoresis of radiolabeled virus. The purified virion contains at least eight structural proteins, with estimated molecular weights of 251K, 90K, 71K, 68K, 65K, 51K, 35K, and 21K, respectively. Three of the polypeptides (71K, 65K, and 51K) were identified as glycoproteins based on their incorporation of [3H]glucosamine. Disruption of the virus by Triton X-100 in the presence of increasing salt concentrations indicated that the polypeptides of molecular weights 251K, 90K, 68K, and 21K were components of the nucleocapsid. In parainfluenza virus 3 infected BS-C-1 cells, seven virus structural polypeptides were identified. Six structural proteins (90K, 71K, 68K, 51K, 35K, and 21K) were detected in the cell lysate at 7 hr after infection, while at 10 hr an additional polypeptide (251K) was also observed. At least two nonstructural polypeptides of molecular weights 30K and 25K were also detected in infected cells. mRNAs isolated from virus-infected cells were translated in a cell-free protein-synthesizing system. The in vitro translation products were identical to the authentic virion polypeptides as determined by partial digestion with staphylococcal V8 protease.

Respiratory syncytial virus fusion glycoprotein: nucleotide sequence of mRNA, identification of cleavage activation site and amino acid sequence of N-terminus of F1 subunit

The amino acid sequence of respiratory syncytial virus fusion protein (Fo) was deduced from the sequence of a partial cDNA clone of mRNA and from the 5' mRNA sequence obtained by primer extension and dideoxysequencing. The encoded protein of 574 amino acids is extremely hydrophobic and has a molecular weight of 63371 daltons. The site of proteolytic cleavage within this protein was accurately mapped by determining a partial amino acid sequence of the N-terminus of the larger subunit (F1) purified by radioimmunoprecipitation using monoclonal antibodies. Alignment of the N-terminus of the F1 subunit within the deduced amino acid sequence of Fo permitted us to identify a sequence of lys-lys-arg-lys-arg-arg at the C-terminus of the smaller N-terminal F2 subunit that appears to represent the cleavage/activation domain. Five potential sites of glycosylation, four within the F2 subunit, were also identified. Three extremely hydrophobic domains are present in the protein; a) the N-terminal signal sequence, b) the N-terminus of the F1 subunit that is analogous to the N-terminus of the paramyxovirus F1 subunit and the HA2 subunit of influenza virus hemagglutinin, and c) the putative membrane anchorage domain near the C-terminus of F1.

Characterization of the 10 proteins of human respiratory syncytial virus: identification of a fourth envelope-associated protein

A total of 13 respiratory syncytial (RS) virus specific polypeptides were identified by pulse-chase metabolic labeling of infected HEp-2 cells. Ten of the 13 proteins were shown to be unique. They were the L, G, F (F1, F2), N, P, M, 24K, 14K, 11K and 9.5K proteins. These conclusions were based on peptide mapping and on previous work showing that each of 10 polypeptides are coded for by a unique mRNA. The seven largest proteins, L, G, F (F1, F2), N, P, M and 24K were identified clearly as virion structural proteins. The 24K protein was characterized by detergent and salt dissociation studies as an envelope-associated protein, bringing to four (G, F (F1, F2), M and 24K) the number of membrane associated proteins for RS virus. A fourth membrane-associated protein has not been described previously for any other paramyxovirus. Of the three smallest proteins, the 14K and 11K were characterized as non-structural proteins. The 9.5K protein was detected in low amounts in highly purified preparations of virions.

Antibody response to respiratory syncytial virus structural proteins in children with acute respiratory syncytial virus infection

The purified respiratory syncytial virus (RSV), Randall strain contained 10 polypeptides (72,000 molecular weight [72K], 66K, 48K, 42K, 40K, 36K, 30K, 23K, 18K, and 15K), 8 of which proved to be virus specific, and polypeptides 48K and 23K were glycosylated. In addition, a high-molecular-weight (150K), virus-specific glycopolypeptide was immunoprecipitated from RSV-infected cell lysate. The antibody response in human sera serially collected from children with primary RSV infection was mainly directed against the polypeptides 30K, 48K, and 72K. The immune response against the other viral proteins was also already detectable in the acute-phase sera. These results indicate that the immune response in RSV infection differs significantly from those for other diseases caused by paramyxoviruses.

Sequence analysis of the respiratory syncytial virus phosphoprotein gene

A recombinant cDNA plasmid (pRSA3) containing an almost full-length copy of the mRNA encoding respiratory syncytial virus phosphoprotein was identified in a cDNA library prepared with mRNA from respiratory syncytial virus-infected cells. The cDNA insert was sequenced, and a protein of 27,150 daltons was deduced from the DNA sequence. The protein is relatively acidic, containing two clusters of acidic amino acids, one in the middle of the molecule and the other at the C-terminus. It is devoid of both cysteine and tryptophan. There was no other potential reading frame within the phosphoprotein gene of respiratory syncytial virus. This situation is unlike that with Sendai virus, a paramyxovirus, which has a nonstructural C protein encoded by a second overlapping reading frame near the 5' end of the mRNA for phosphoprotein.

Use of the biotin-avidin system to study the specificity of antibodies against respiratory syncytial virus

To characterize the specificity of monoclonal antibodies against respiratory syncytial virus, we developed a technique which combined the biotin-avidin system, immunoprecipitation, and transblot electrophoresis. The viral proteins were first biotinylated and then immunoprecipitated with a monoclonal antibody or respiratory syncytial virus immune serum, separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and electrophoretically transferred to nitrocellulose paper. The protein bands were located on the paper with avidin-peroxidase plus a precipitable substrate. This procedure gave reproducible results qualitatively similar to those obtained by radioimmunoprecipitation but without the cost, risk of radiation exposure, or disposal problems of radioisotopes. This procedure should have widespread applications.

Monoclonal antibodies protect against respiratory syncytial virus infection in mice

Twenty-five monoclonal antibodies (Mab) to respiratory syncytial virus (RSV) and two to hepatitis B virus were inoculated intravenously into mice. Twenty-four hours later the mice were challenged intranasally with RSV. Eleven of 14 Mab against fusion protein and four out of six Mab against a larger glycoprotein (GP84) significantly reduced the titre of RSV in the lungs when mice were killed 5 days later. Five Mab against three other RSV proteins and two Mab against hepatitis B virus had no significant effect on RSV infection. These results indicated that serum IgG against one epitope on the fusion protein and another on the larger glycoprotein (GP84) will completely protect mice against challenge. These epitopes are primary candidates for an RSV vaccine produced by techniques of gene cloning and peptide synthesis.

Nucleotide sequence of the gene encoding respiratory syncytial virus matrix protein

The amino acid sequence of the matrix protein of the human respiratory syncytial virus (RS virus) was deduced from the sequence of a cDNA insert in a recombinant plasmid harboring an almost full-length copy of this gene. It specifically hybridized to a single 1,050-base mRNA from infected cells. The recombinant containing 944 base pairs of RS viral matrix protein gene sequence lacked five nucleotides corresponding to the 5' end of the mRNA. The nucleotide sequence of the 5' end of the mRNA was determined by the dideoxy sequencing method and found to be 5' NGGGC, wherein the C residue is one nucleotide upstream of the cloned viral sequence. The initiator ATG codon for the matrix protein is embedded in an AATATGG sequence similar to the canonical PXXATGG sequence present around functional eucaryotic translation initiation codons. There is no conserved sequence upstream of the polyadenylate tail, unlike vesicular stomatitis virus and Sendai virus, in which four nucleotides upstream of the polyadenylate tail are conserved in all genes. There is no equivalent of the eucaryotic polyadenylation signal AAUAAA upstream of the polyadenylate tail. The matrix protein of 28,717 daltons has 256 amino acids. It is relatively basic and moderately hydrophobic. There are two clusters of hydrophobic amino acid residues in the C-terminal third of the protein that could potentially interact with the membrane components of the infected cell. The matrix protein has no homology with the matrix proteins of other negative-strand RNA viruses, implying that RS virus has undergone extensive evolutionary divergence. A second open reading frame potentially encoding a protein of 75 amino acids and partially overlapping the C terminus of the matrix protein was also identified.

Identification of a tenth mRNA of respiratory syncytial virus and assignment of polypeptides to the 10 viral genes

Nine mRNAs, their cDNA clones, and a genome transcriptional map have been reported previously for respiratory syncytial virus (P. L. Collins and G. W. Wertz, Proc. Natl. Acad. Sci. U.S.A. 80:3208-3212, 1983). We report here the identification of a 10th viral mRNA, designated mRNA 2b (molecular weight [MW] ca. 0.39 X 10(6)), that was detected by RNA (Northern) blot hybridization with cDNA clones. Analysis of a polycistronic readthrough transcript was used to deduce the position in the viral transcriptional map of the gene encoding the newly identified mRNA. The polypeptide coding assignments of 9 of the 10 respiratory syncytial virus mRNAs were determined. Individual viral mRNAs were purified by hybridization selection with nine unique, nonoverlapping cDNA clones and analyzed by translation in vitro. Each of the nine mRNAs encoded a single polypeptide chain. The coding assignments were as follows: RNA 1a (MW ca. 0.24 X 10(6)), a 9,500-dalton (9.5K) protein; RNA 1b (MW 0.26 X 10(6)), an 11K protein; RNA 1c (MW 0.26 X 10(6)), a 14K protein; RNA 2a (MW 0.38 X 10(6)), the 34K phosphorylated (P) protein; RNA 2b (MW 0.39 X 10(6)), a 36K protein; RNA 3a (MW 0.40 X 10(6)), the 26K matrix (M) protein; RNA 3b (MW 0.40 X 10(6)), a 24K protein; RNA 4 (MW 0.47 X 10(6)), the 42K major nucleocapsid (N) protein; and RNA 5 (MW 0.74 X 10(6)), a 59K protein. The cDNA clones used for the hybridization selections were respiratory syncytial virus specific and did not hybridize with uninfected-cell mRNA; therefore the proteins synthesized with the selected mRNAs were virus specific. The 9.5K, 11K, 14K, 24K, M, P, 36K, N, and 59K proteins were encoded by different mRNAs; therefore these nine proteins are all unique. The 9.5K, 11K, 14K, 24K, M, P, and N proteins synthesized in vitro with hybrid-selected mRNAs each had counterparts with the same electrophoretic mobilities in extracts of virus-infected cells. The in vitro polypeptides and their authentic counterparts were shown to be closely related by limited digest peptide mapping. The 36K and 59K polypeptides lacked counterparts with the same electrophoretic mobilities in infected cells and therefore are candidates for the unprocessed precursors of the viral F and G glycoproteins. The 10th viral mRNA, the 2,500K RNA 7, was not tested directly but is the only known mRNA of the appropriate size to encode the 200K large (L) protein of the viral nucleocapsid. These assignments account for all 10 of the reported viral mRNAs and bring to 10 the number of known unique viral proteins.

Enzymatic cleavage of a glycoprotein of respiratory syncytial virus

The 75K glycoprotein of the A2 strain of respiratory syncytial virus was cleaved by digestion with trypsin or Staphylococcus aureus protease V8. The fragments resulting from trypsin digestion were 40K and 29K; those from the Staphylococcal protease were 49K and 37K.

Respiratory syncytial virus glycoproteins

The proteins of respiratory syncytial (RS) virus were analyzed by SDS-polyacrylamide gel electrophoresis. Eight virion structural proteins with molecular weights of 180,000, 89,000, 48,000, 42,000, 34,000, 28,000, 25,000, and 21,000 were identified. These proteins were given tentative designations of L (180,000), G (89,000), F1 (48,000), NP (42,000), P (34,000), M (28,000), Vp25 (25,000), and F2 (21,000). The 89,000-, 48,000-, and 21,000-dalton polypeptides were glycosylated and could be purified on lentil-lectin sepharose columns. All three glycoproteins could be immunoprecipitated from extracts of infected cells but not from uninfected cells, suggesting that they are viral specified. The host cell affected the apparent molecular weights of the largest and smallest glycosylated polypeptides possibly by differences in glycosylation. The 48,000- and 21,000-dalton glycopolypeptides were disulfide linked subunits of a 68,000-dalton glycoprotein that was seen on unreduced gels. The 68,000-dalton glycoprotein was thus similar to the fusion (F) protein of paramyxoviruses. Treatment of infected cultures with tunicamycin, a drug that blocks glycosylation, inhibited syncytial formation and resulted in over a 1000-fold reduction of extracellular infectious virus. Virions purified from tunicamycin-treated cells had reduced amounts of all three glycosylated proteins. No new forms of these proteins were conclusively identified, suggesting that unglycosylated forms of RS glycoproteins were not incorporated into virion membranes.

Amino acid sequence of human respiratory syncytial virus nucleocapsid protein

Amino acid sequence of the human respiratory syncytial (RS) virus nucleocapsid (NC) protein, deduced from the DNA sequence of a recombinant plasmid, is presented. The cDNA plasmid (pRSB11) has 1412 bp of RS viral NC sequence and lacks six nucleotides of the 5' end of mRNA. There is a single long open reading frame encoding 467 amino acids. This 51540 dal protein is rich in basic amino acids and has no homologies with other known viral capsid proteins.

Modified immunoprecipitation procedure for the identification of human respiratory syncytial virus polypeptides

When analysed by polyacrylamide gel electrophoresis, human respiratory syncytial virus harvested after a one step growth cycle and purified through a continuous sucrose density gradient was shown to be composed of nine structural proteins of 90, 68, 49, 42, 34, 28, 25, 19 an 13 kd. The 90, 49 and 19 kd polypeptides were identified as glycopolypeptides by glucosamine incorporation. A modified immunoprecipitation procedure confirmed the viral specificity of the 49, 42, 28, 25 and 19 kd polypeptides.

Monoclonal antibodies to respiratory syncytial virus proteins: identification of the fusion protein

Six monoclonal antibodies directed against respiratory syncytial virus proteins were produced. Each was characterized by immunoprecipitation and indirect immunofluorescence. One was directed against the nucleocapsid protein. NP 44, two were directed against a 37,000-dalton protein, two were directed against the major envelope glycoprotein, GP 90, and one was directed against the 70,000-dalton envelope protein, VP 70. Indirect immunofluorescence stain patterns of infected HEp-2 cells defined GP 90 and VP 70 as viral proteins expressed on the cell surface, whereas NP 44 and the 37,000-dalton protein were detected as intracytoplasmic inclusions. One of the anti-GP 90 antibodies neutralized virus only in the presence of complement but did not inhibit cell-cell fusion. The anti-VP 70 antibody neutralized virus without complement and inhibited cell-cell fusion of previously infected HEp-2 cells, thus identifying VP 70 as the fusion protein.

Respiratory syncytial virus mRNA coding assignments

The polypeptide coding assignments for six of the respiratory syncytial virus-specific mRNAs were determined by translation of the individual mRNAs in vitro. The coding assignments of the RNAs are as follows. RNA band 1 is complex and can be separated into at least two components on the basis of electrophoretic mobility (molecular weights [MWs] approximately equal to 0.21 X 10(6) and 0.31 X 10(6), respectively) that code for three polypeptides of 9.5, 11, and 14 kilodaltons (K). RNA 2 (MW, 0.39 X 10(6)) codes for a 34K polypeptide; RNA 3 (MW, 0.40 X 10(6)) codes for a 26K polypeptide; RNA 4 (MW, 0.47 X 10(6)) codes for a 42K polypeptide; and RNA 5 (MW, 0.74 X 10(6)) codes for a 59K polypeptide. By limited-digest peptide mapping, the 34, 26, and 42K polypeptides synthesized in vitro appeared to be unique. Additionally, peptide mapping showed that the 34, 26, and 42K polypeptides synthesized in vitro were indistinguishable from their counterparts synthesized in infected cells. Thus, the 34, 26, and 42K polypeptides coded for by mRNAs 2, 3, and 4, respectively, were identified as the respiratory syncytial virus phosphoprotein (34K), matrix protein (26K), and nucleocapsid protein (42K), respectively. RNA 5 was shown to code for a 59K polypeptide. The 59K polypeptide synthesized in vitro did not comigrate with any polypeptide specific to infected cells, suggesting that it is a candidate for co- or post-translational modification.

Construction and characterization of cDNA clones for four respiratory syncytial viral genes

Cytoplasmic poly(A)-containing RNA from respiratory syncytial virus-infected cells was used as a template to synthesize oligo(dT)-primed cDNAs. Discrete size classes of single-stranded cDNAs, resolved by alkali agarose gel electrophoresis, were used separately to construct double-stranded cDNAs that were subsequently inserted into the plasmid vector pBR322 at the Pst I site by means of oligo(dG)oligo(dC) tailing. After transfection of Escherichia coli, recombinant plasmids were screened mostly by serial rounds of hybrid selection of mRNAs from virus-infected cells and subsequent in vitro translation of the selected mRNAs. Comparative peptide mapping of the translation products with those of authentic virion proteins served to establish the viral origin of the cDNA recombinants. In this manner, four distinct classes of recombinant plasmids were identified. These encode sequences corresponding to those of respiratory syncytial virus nucleocapsid protein, matrix protein, phosphoprotein, and a nonstructural protein.

Immunochemical identification of viral and nonviral proteins of the respiratory syncytial virus virion

We identified by immunochemical methods 13 polypeptides associated with the infectious respiratory syncytial virus virion. Eight of these polypeptides (VP200, VP84, VP66, VP43, VP40, VP37, VP28, and VP19) were identified as virus specific. Two other polypeptides, (VP) 22 and (VP) 12, are provisionally considered to be of viral origin. Three nonviral proteins are also intimately associated with the infectious virion. These nonviral proteins were identified as cellular actin and two proteins with bovine serum albumin immunospecificity. VP40 was identified as the major ribonucleoprotein. Based on biochemical and biophysical similarities with paramyxovirus proteins, other respiratory syncytial virus proteins are believed to have these specific viral functions: VP84, "hemagglutinin"; VP66, undissociated fusion protein, F1,2; VP43, F1; and VP19, F2, VP66 contains a major determinant involved in viral infectivity since all neutralizing antibodies tested, including a monoclone, precipitated this protein.

Analysis of proteins synthesized in respiratory syncytial virus-infected cells

The spectrum of respiratory syncytial virus-encoded proteins was examined in infected cell extracts by standard polyacrylamide gel electrophoresis and by two-dimensional gel analysis. Polyacrylamide gel electrophoresis analysis of a variety of respiratory syncytial virus-infected, actinomycin D-treated cell lines revealed the presence of as many as nine virus-encoded proteins. Seven of these nine proteins were immunoprecipitated by anti-respiratory syncytial serum. Only one major band of [3H]glucosamine was detected in infected cell extracts (Vp86), whereas the reported major virion glycoprotein (Vp48-53) was difficult to detect in infected cells when carbohydrate labels were employed. Two-dimensional gel analysis easily identified seven viral proteins, and one other was tentatively identified. The reported major virion glycoprotein again was not consistently detected. The results of this study confirm the existence of a virus-coded glycoprotein (Vp86) in infected cell extracts. The existence of this glycoprotein in the purified virion has been in dispute, but the apparent low methionine content of this protein may be the reason for this controversy.