Analysis of Sendai virus mRNAs with cDNA clones of viral genes and sequences of biologically important regions of the fusion protein

Type II integral membrane protein, TM of J paramyxovirus promotes cell-to-cell fusion

Paramyxoviruses include many important animal and human pathogens. Most paramyxoviruses have two integral membrane proteins: fusion protein (F) and attachment proteins hemagglutinin, hemagglutinin-neuraminidase, or glycoprotein (G), which are critical for viral entry into cells. J paramyxovirus (JPV) encodes four integral membrane proteins: F, G, SH, and transmembrane (TM). The function of TM is not known. In this work, we have generated a viable JPV lacking TM (JPV∆TM). JPV∆TM formed opaque plaques compared with JPV. Quantitative syncytia assays showed that JPV∆TM was defective in promoting cell-to-cell fusion (i.e., syncytia formation) compared with JPV. Furthermore, cells separately expressing F, G, TM, or F plus G did not form syncytia whereas cells expressing F plus TM formed some syncytia. However, syncytia formation was much greater with coexpression of F, G, and TM. Biochemical analysis indicates that F, G, and TM interact with each other. A small hydrophobic region in the TM ectodomain from amino acid residues 118 to 132, the hydrophobic loop (HL), was important for syncytial promotion, suggesting that the TM HL region plays a critical role in cell-to-cell fusion.

Microbiological Quality Control for Laboratory Rodents and Lagomorphs

Mice (Mus musculus), rats (Rattus norvegicus), other rodent species, and domestic rabbits (Oryctolagus cuniculus) have been used in research for over 100 years. During the first half of the 20th century, microbiological quality control of lab animals was at best rudimentary as colonies were conventionally housed and little or no diagnostic testing was done. Hence, animal studies were often curtailed and confounded by infectious disease (Mobraaten and Sharp, 1999; Morse, 2007; Weisbroth, 1999). By the 1950s, it became apparent to veterinarians in the nascent field of comparative medicine that disease-free animals suitable for research could not be produced by standard veterinary disease control measures (e.g., improved sanitation and nutrition, antimicrobial treatments) in conventional facilities. Henry Foster, the veterinarian who founded Charles River Breeding Laboratories in 1948 and a pioneer in the large-scale production of laboratory rodents, stated in a seminar presented at the 30th anniversary of AALAS, “After a variety of frustrating health-related problems, it was decided that a major change in the company’s philosophy was required and an entirely different approach was essential”. Consequently, he and others developed innovative biosecurity systems to eliminate and exclude pathogens (Allen, 1999). In 1958, Foster reported on the Cesarean-originated barrier-sustained (COBS) process for the large-scale production of specific pathogen-free (SPF) laboratory rodents (Foster, 1958). To eliminate horizontally transmitted pathogens, a hysterectomy was performed on a near-term dam from a contaminated or conventionally housed colony. The gravid uterus was pulled through a disinfectant solution into a sterile flexible film isolator where the pups were removed from the uterus and suckled on axenic (i.e., germ-free) foster dams. After being mated to expand their number and associated with a cocktail of nonpathogenic bacteria to normalize their physiology and prime their immune system, rederived rodents were transferred to so-called barrier rooms for large-scale production. The room-level barrier to adventitious infection entailed disinfection of the room, equipment, and supplies, limiting access to trained and properly gowned personnel, and the application of new technologies such as high-efficiency particulate air-filtration of incoming air (Dubos and Schaedler, 1960; Foster, 1980; Schaedler and Orcutt, 1983; Trexler and Orcutt, 1999). The axenic and associated rodents mentioned in the COBS process are collectively classified as gnotobiotic to indicate that they have a completely known microflora. By contrast, barrier-reared rodent colonies are not gnotobiotic because they are housed in uncovered cages and thus acquire a complex microflora from the environment, supplies, personnel, and other sources. Instead, they are described as SPF to indicate that according to laboratory testing, they are free from infection with a defined list of infectious agents, commonly known as an ‘exclusion’ list.

Role of sequence and structure of the Hendra fusion protein fusion peptide in membrane fusion

Viral fusion proteins are intriguing molecular machines that undergo drastic conformational changes to facilitate virus-cell membrane fusion. During fusion a hydrophobic region of the protein, termed the fusion peptide (FP), is inserted into the target host cell membrane, with subsequent conformational changes culminating in membrane merger. Class I fusion proteins contain FPs between 20 and 30 amino acids in length that are highly conserved within viral families but not between. To examine the sequence dependence of the Hendra virus (HeV) fusion (F) protein FP, the first eight amino acids were mutated first as double, then single, alanine mutants. Mutation of highly conserved glycine residues resulted in inefficient F protein expression and processing, whereas substitution of valine residues resulted in hypofusogenic F proteins despite wild-type surface expression levels. Synthetic peptides corresponding to a portion of the HeV F FP were shown to adopt an α-helical secondary structure in dodecylphosphocholine micelles and small unilamellar vesicles using circular dichroism spectroscopy. Interestingly, peptides containing point mutations that promote lower levels of cell-cell fusion within the context of the whole F protein were less α-helical and induced less membrane disorder in model membranes. These data represent the first extensive structure-function relationship of any paramyxovirus FP and demonstrate that the HeV F FP and potentially other paramyxovirus FPs likely require an α-helical structure for efficient membrane disordering and fusion.

Chapter 9 Fusion of Viral Envelopes with Cellular Membranes

This chapter reviews some characteristic features of membrane fusion activity for each virus and discusses the mechanisms of membrane fusion, especially low pH-induced membrane fusion. It concentrates on the interaction of the hydrophobic segment with the target cell membrane lipid bilayer and suggests the entrance of the segment into the lipid bilayer hydrophobic core as a key step in fusion. The envelope is a lipid bilayer membrane with the virus specific glycoproteins spanning it. The bilayer originates from the host cell membrane and has a lipid composition and transbilayer distribution quite similar to the host's. The viral glycoproteins have the functions of binding to the target cell surface and fusion with the cell membranes. The two functions are carried by a single glycoprotein in influenza virus (HA), vesicular stomatitis virus (VSV) G glycoprotein, and Semliki Forest virus SFV E glycoprotein. In Sendai virus (HVJ), the functions are carried by separate glycoproteins, hemagglutinin-neuraminidase (HN) for binding and fusion glycoprotein (F) for fusion. When viruses encounter target cells, they first bind to the cell surface through an interaction of the viral glycoprotein with receptors.

F0-containing noninfectious Sendai virus can initiate replication in mouse lungs but requires a relatively long incubation period

The replication of LLC-MK2-grown noninfectious Sendai virus, containing exclusively fusion (F) glycoprotein precursors, was examined in the mouse lung to study the accessibility of virus inoculated intranasally to the virus activator present in the lung. When mice were intranasally inoculated with various doses of the virus after in vitro activation with trypsin, the 50% mouse infectious dose (MID50) was determined to be 0.7 cell-infectious units (CIU) per mouse, indicating that one infectious unit of Sendai virus is enough to initiate replication in the mouse lung and that the present experimental system is highly sensitive. On the other hand, in mice inoculated with virus not treated with trypsin, virus replication in the lung was recognized even in mice inoculated with samples containing no infectious virus, and the MID50 was determined to be 67.5 CIU per mouse (here, CIU were assayed after in vitro trypsin treatment). When mice were infected with 20 MID50 of trypsin-treated infectious and untreated noninfectious viruses (an approximately 100-fold greater amount of noninfectious virus than of infectious virus was used), the noninfectious virus was found to require 2 more days of incubation than the infectious virus, and many of the F proteins synthesized in the lungs of mice infected with the F0-containing virus were present in the cleaved form. In addition, the infection of mice with noninfectious virus was strongly suppressed by aprotinin, a serine protease inhibitor. These results indicate that Sendai virus can initiate replication in the mouse lung even with the F0-containing noninfectious virus and strongly suggest that this infection process is mediated by cleavage activation of the F0 proteins of inoculated viruses by a serine protease(s) present in the lumen of the mouse respiratory tract but that activation of the noninfectious virus is an inefficient process.

Tryptase Clara, an activating protease for Sendai virus in rat lungs, is involved in pneumopathogenicity

Tryptase Clara is an arginine-specific serine protease localized exclusively in and secreted from Clara cells of the bronchial epithelium of rats (H. Kido, Y. Yokogoshi, K. Sakai, M. Tashiro, Y. Kishino, A. Fukutomi, and N. Katunuma, J. Biol. Chem. 267:13573-13579, 1992). The purified protease was shown in vitro to behave similarly to trypsin, cleaving the precursor glycoprotein F of Sendai virus at residue Arg-116 and activating viral infectivity in a dose-dependent manner. Anti-tryptase Clara antibody inhibited viral activation by the protease in vitro in lung block cultures and in vivo in infected rats. When the enzyme-specific antibody was administered intranasally to rats that were also infected intranasally with Sendai virus, activation of progeny virus in the lungs was significantly inhibited. Thus, multiple cycles of viral replication were suppressed, resulting in a reduction in lung lesions and in the mortality rate. These findings indicate that tryptase Clara is an activating protease for Sendai virus in rat lungs and is therefore involved in pulmonary pathogenicity of the virus in rats.

Studies on the fusion peptide of a paramyxovirus fusion glycoprotein: roles of conserved residues in cell fusion

The role of residues in the conserved hydrophobic N-terminal fusion peptide of the paramyxovirus fusion (F) protein in causing cell-cell fusion was examined. Mutations were introduced into the cDNA encoding the simian virus 5 (SV5) F protein, the altered F proteins were expressed by using an eukaryotic vector, and their ability to mediate syncytium formation was determined. The mutant F proteins contained both single- and multiple-amino-acid substitutions, and they exhibited a variety of intracellular transport properties and fusion phenotypes. The data indicate that many substitutions in the conserved amino acids of the simian virus 5 F fusion peptide can be tolerated without loss of biological activity. Mutant F proteins which were not transported to the cell surface did not cause cell-cell fusion, but all of the mutants which were transported to the cell surface were fusion competent, exhibiting fusion properties similar to or better than those of the wild-type F protein. Mutant F proteins containing glycine-to-alanine substitutions had altered intracellular transport characteristics, yet they exhibited a great increase in fusion activity. The potential structural implications of this substitution and the possible importance of these glycine residues in maintaining appropriate levels of fusion activity are discussed.

Organ tropism of Sendai virus in mice: proteolytic activation of the fusion glycoprotein in mouse organs and budding site at the bronchial epithelium

Wild-type Sendai virus is exclusively pneumotropic in mice, while a host range mutant, F1-R, is pantropic. The latter was attributed to structural changes in the fusion (F) glycoprotein, which was cleaved by ubiquitous proteases present in many organs (M. Tashiro, E. Pritzer, M. A. Khoshnan, M. Yamakawa, K. Kuroda, H.-D. Klenk, R. Rott, and J. T. Seto, Virology 165:577-583, 1988). These studies were extended by investigating, by use of an organ block culture system of mice, whether differences exist in the susceptibility of the lung and the other organs to the viruses and in proteolytic activation of the F protein of the viruses. Block cultures of mouse organs were shown to synthesize the viral polypeptides and to support productive infections by the viruses. These findings ruled out the possibility that pneumotropism of wild-type virus results because only the respiratory organs are susceptible to the virus. Progeny virus of F1-R was produced in the activated form as shown by infectivity assays and proteolytic cleavage of the F protein in the infected organ cultures. On the other hand, much of wild-type virus produced in cultures of organs other than lung remained nonactivated. The findings indicate that the F protein of wild-type virus was poorly activated by ubiquitous proteases which efficiently activated the F protein of F1-R. Thus, the activating protease for wild-type F protein is present only in the respiratory organs. These results, taken together with a comparison of the predicted amino acid substitutions between the viruses, strongly suggest that the different efficiencies among mouse organs in the proteolytic activation of F protein must be the primary determinant for organ tropism of Sendai virus. Additionally, immunoelectron microscopic examination of the mouse bronchus indicated that the budding site of wild-type virus was restricted to the apical domain of the epithelium, whereas budding by F1-R occurred at the apical and basal domains. Bipolar budding was also observed in MDCK monolayers infected with F1-R. The differential budding site at the primary target of infection may be an additional determinant for organ tropism of Sendai virus in mice.

Interprotein disulfide bonding between F and G glycoproteins of human respiratory syncytial virus

The envelope glycoprotein G, of human respiratory virus was purified by immunoaffinity chromatography using a monoclonal antibody reacting with G glycoprotein. The purified material was analyzed for its protein patterns and by western blot for its reactivity with specific monoclonal antibodies. In addition to the G specific proteins at 90 and 55 kilodalton (kDa) range, high molecular weight species were coeluted with G protein. Three high molecular weight species were noticed: one (140 kDa) reacting with fusion protein (F) monoclonal antibody and two other species (230 and 195 kDa) reacting with both fusion protein and G protein monoclonal antibodies. The protein reacting only with F monoclonal antibody consists of fusion protein dimer. Western blot and two dimensional gel electrophoretic analysis revealed that each of the other two complexes is composed of two moles of F protein and one mole of G protein. These two complexes differ in their molecular sizes depending on whether G is in the form of 90 or 55 kDa. Upon heat denaturation, fusion protein monomer (70 kDa) is released from the complex, leaving the two complexes, consisting of one mole of F protein and one mole of G protein (160 and 125 kDa species respectively). Disulfide-reducing agents are required to break the monomers of F and G complexes. These results provide a direct evidence for the presence of envelope glycoprotein complexes linked by interprotein disulfide bonding. This may have implications on the structural and functional properties of envelope glycoproteins.

Analysis of the relationship between cleavability of a paramyxovirus fusion protein and length of the connecting peptide

The relationship between the length of the connecting peptide in a paramyxovirus F0 protein and cleavage of F0 into the F1 and F2 subunits has been examined by constructing a series of mutant F proteins via site-directed mutagenesis of a cDNA clone encoding the simian virus 5 F protein. The mutant F proteins had one to five arginine residues deleted from the connecting peptide. The minimum number of arginine residues required for cleavage-activation of the simian virus 5 F0 protein by host cell proteases was found to be four. F proteins with two or three arginine residues in the connecting peptide were not cleaved by host cell proteases but could be cleaved by exogenously added trypsin. The mutant F protein possessing a connecting peptide consisting of one arginine residue was not cleaved by trypsin. The altered F proteins were all transported to the infected-cell plasma membrane as shown by cell surface immunofluorescence or cell surface trypsinization. However, the only mutant F protein found to be biologically active as detected by syncytium formation was the F protein which has four arginine residues at the cleavage site. The results presented here suggest that in the paramyxovirus F protein the number of basic amino acid residues in the connecting peptide is important for cleavage of the precursor protein by host cell proteases but is not the only structural feature involved. In addition, the data indicate that cleavage of F0 into F1 and F2 does not necessarily result in biological activity and that the connecting peptide may affect the local conformation of the F polypeptide.

Computer analysis suggests a role for signal sequences in processing polyproteins of enveloped RNA viruses and as a mechanism of viral fusion

We have used a computer program to scan the entire sequence of viral polyproteins for eucaryotic signal sequences. The method is based on that of von Heijne (1). The program calculates a score for each residue in a polyprotein. The score indicates the resemblance of each residue to that at the cleavage site of a typical N-terminal eucaryotic signal sequence. The program correctly predicts the known N-terminal signal sequence cleavage sites of several cellular and viral proteins. The analysis demonstrates that the polyproteins of enveloped RNA viruses--including the alphaviruses, flaviviruses, and bunyaviruses--contain several internal signal-sequence-like regions. The predicted cleavage site in these internal sequences are often known cleavage sites for processing of the polyprotein and are amongst the highest scoring residues with this algorithm. These results indicate a role for the cellular enzyme signal peptidase in the processing of several viral polyproteins. Not all high-scoring residues are sites of cleavage, suggesting a difference between N-terminal and internal signal sequences. This may reflect the secondary structure of the latter. Signal sequences were also found at the N-termini of the fusion proteins of the paramyxoviruses and the retroviruses. This suggests a mechanism of viral fusion analogous to that by which proteins are translocated through the membranes of the endoplasmic reticulum at synthesis.

The molecular biology of influenza virus pathogenicity

It is an accepted concept that the pathogenicity of a virus is of polygenic nature. Because of their segmented genome, influenza viruses provide a suitable system to prove this concept. The studies employing virus mutants and reassortants have indicated that the pathogenicity depends on the functional integrity of each gene and on a gene constellation optimal for the infection of a given host. As a consequence, virtually every gene product of influenza virus has been reported to contribute to pathogenicity, but evidence is steadily growing that a key role has to be assigned to hemagglutinin. As the initiator of infection, hemagglutinin has a double function: (1) promotion of adsorption of the virus to the cell surface, and (2) penetration of the viral genome through a fusion process among viral and cellular membranes. Adsorption is based on the binding to neuraminic acid-containing receptors, and different virus strains display a distinct preference for specific oligosaccharides. Fusion capacity depends on proteolytic cleavage by host proteases, and variations in amino acid sequence at the cleavage site determine whether hemagglutinin is activated in a given cell. Differences in cleavability and presumably also in receptor specificity are important determinants for host tropism, spread of infection, and pathogenicity. The concept that proteolytic activation is a determinant for pathogenicity was originally derived from studies on avian influenza viruses, but there is now evidence that it may also be relevant for the disease in humans because bacterial proteases have been found to promote the development of influenza pneumonia in mammals.

Nucleotide sequence of the bovine parainfluenza 3 virus genome: its 3' end and the genes of NP, P, C and M proteins

We present the nucleotide sequence of bovine parainfluenza 3 virus (BPIV3) genome from its 3' end to the opening region of the F gene, through the NP, P plus C, and M genes. Comparison of the sequence with those reported for other paramyxoviruses indicated that BPIV3 was most similar to human parainfluenza 3 virus (HPIV3), and also very similar to Sendai virus in the structural make-up of its genome and the amino acid sequences of its gene products, suggesting that these three viruses constitute a paramyxovirus subgroup from which Newcastle disease and measles viruses are separable. In BPIV3 and Sendai virus, the NP and M proteins, the main structural elements, were more highly conserved than the functionally important P and C proteins. This tendency was also observed even in BPIV3 and HPIV3. Virus-specific amino acid sequences of the NP and M proteins were found at the carboxyl and amino terminal regions, respectively. BPIV3 M mRNA was found to have aberrations in its poly A attachment site.

Nucleotide sequence of the bovine parainfluenza 3 virus genome: the genes of the F and HN glycoproteins

By analysing complementary DNA clones constructed from genomic RNA of bovine parainfluenza 3 virus (BPIV3), we determined the nucleotide sequence of the region containing the entire F and HN genes. Their deduced amino acid sequences showed about 80% homologies with those of human parainfluenza 3 virus (HPIV3), about 45% with those of Sendai virus, and about 20% with those of SV5 and Newcastle disease virus (NDV), indicating, together with the results described in the preceding paper on the NP, P, C and M proteins of BPIV3, that BPIV3, HPIV3 and Sendai virus constitute a paramyxovirus subgroup, and that BPIV3 and HPIV3 are very closely related. The F and HN proteins of all these viruses, including SV5 and NDV, however, were shown to have protein-specific structures as well as short but well-conserved amino acid sequences, suggesting that these structures and sequences are related to the activities of these glycoproteins.

A putative protein-sequestration site involving intermediate filaments for protein degradation by autophagy. Studies with transplanted Sendai-viral envelope proteins in HTC cells

Reconstituted Sendai-viral envelopes (RSVE) were fused with hepatoma tissue-culture (HTC) cells, thereby introducing viral membrane glycoproteins into the plasma membrane [Earl, Billett, Hunneyball & Mayer (1987) Biochem. J. 241, 801-807]. Fractionation of homogenized cells on Nycodenz gradients shows that much of the viral 125I-labelled HN and F proteins were rapidly sequestered into a dense fraction distinct from fractions containing plasma membrane, lysosomes and mitochondria. Electron microscopy (results not shown) indicates that the dense fraction contains nuclear residues, multivesicular structures, dense bodies and fibrous structures. Both the dense fraction and a hexosaminidase-enriched fraction contain trichloroacetic acid-insoluble radioactivity, including intact 125I-labelled viral proteins. The viral proteins are progressively transferred from the dense fraction to the hexosaminidase-enriched fraction; the transfer is retarded by 50 micrograms of leupeptin/ml. Trichloroacetic acid-soluble radiolabel is progressively released into the culture medium as the proteins are degraded. Within 5 h after transplantation of viral HN and F proteins into recipient cells, a proportion (approx. 45%) of the 125I-labelled glycoproteins cannot be extracted by sequentially treating cells with digitonin (1 mg/ml), Triton X-100 (1%, w/v) and 0.3 M-KI. HN and F proteins in the non-extractable residue are tightly associated with nuclear-intermediate-filament (vimentin) material, as shown by Western blots and electron microscopy. The viral proteins are progressively transferred out of the nuclear-intermediate-filament residue; the transfer is slowed when cells are cultured with leupeptin. The data are consistent with the notion that transplanted viral HN and F proteins are sequestered to a perinuclear site in tight association with intermediate filaments before transfer into the autophagolysosomal system for degradation.

Drastic immunoreactivity changes between the immature and mature forms of the Sendai virus HN and F0 glycoproteins

The immunoreactivity of the Sendai virus HN and F0 glycoproteins was shown to mature before reaching the final form exhibited by the native mature proteins. The maturation process differed for the two proteins. The native F0 immunoreactivity was shown to be defined cotranslationally, and the addition of high-mannose sugar residues may represent the final step in defining the maturation of immunoreactivity. On the other hand, native HN immunoreactivity was slowly fashioned during the hour after the completion of protein synthesis. Although addition of high-mannose sugar could constitute a necessary step in this slow maturation process, it was shown not to be sufficient. Processing of high-mannose sugars and HN self-association in homodimers and homotetramers were investigated as possible steps involved in the slow maturation of HN immunoreactivity. They were found not to play a significant role. On the other hand, conformational changes presumably took place during the maturation of HN immunoreactivity. Drastic immunoreactivity differences were also demonstrated between the native and denatured forms of the glycoproteins. Possible implications of these results in defining the pathways of glycoprotein synthesis are discussed.

The fusion-related hydrophobic domain of Sendai F protein can be moved through the cytoplasmic membrane of Escherichia coli

Recent work on a prokaryotic membrane protein, gene III protein (pIII) of coliphage f1, showed that polypeptide segments of sufficient hydrophobicity functioned to stop transfer of the polypeptide across the cell membrane: strings of 16 or more hydrophobic amino acids sufficed. A fusion-related hydrophobic domain (FRHD) of Sendai F protein, a sequence of 26 consecutive uncharged residues, has been implicated in the fusion of the viral membrane envelope and the target-cell membrane through a hydrophobic interaction. As it is located on the exterior of the viral membrane, this sequence must be transferred across the host-cell membrane during synthesis. We have inserted either the FRHD or the F protein membrane anchor (the COOH-terminal region of the F protein) into an internal site of a secreted pIII, which lacks its natural membrane anchor. These two hydrophobic sequences behave in the bacteria just as they do in their natural eukaryotic cell host. The F protein membrane anchor functions to stop transfer, conferring a membrane-spanning topology to the F-pIII hybrid protein; however, the FRHD is moved through the cytoplasmic membrane and derivatives carrying this sequence are secreted to the periplasm. We discuss how the FRHD is compatible with passage through the membrane and yet is still able to mediate membrane fusion through a presumed hydrophobic interaction.

Specific inhibition of mRNA translation by complementary oligonucleotides covalently linked to intercalating agents

Synthetic oligodeoxynucleotides that are covalently linked at their 3' end to an acridine derivative and are complementary to the repeated sequence UUAAAUUAAAUUAAA adjacent to the ribosome binding site of the gene 32-encoded mRNA from phage T4 have been used to regulate the synthesis of gene 32-encoded protein in vitro. These modified, synthetic oligonucleotides specifically block the translation of gene 32-encoded mRNA with a higher efficiency than the homologous unsubstituted oligonucleotides. The inhibition produced by these short "anti-messengers" is due to the formation of specific mRNA . oligodeoxynucleotide hybrids that are stabilized by the intercalation of the acridine ring in the RNA . DNA duplex.

Antigenic mapping and functional analysis of the F protein of Newcastle disease virus using monoclonal antibodies

Twelve monoclonal antibodies to the F protein of a velogenic strain of Newcastle disease virus (NDV) were established. Each of these antibodies inhibited virus-induced plaque formation in BHK-21 cells. Seven antibodies neutralized viral infectivity in eggs; thus, antigenic variants could be selected with these antibodies and used for antigenic mapping. Based on the reactivity of the antigenic variants with the antibodies used in selection, 4 distinct antigenic sites (I-IV) were defined on the F protein molecule. In competitive binding assay, sites II and III were found to be spatially close to each other. Each antibody to sites I, II and III inhibited both virus-induced hemolysis of chicken erythrocytes and syncytium formation of BHK-21 cells. On the other hand, some of the antibodies to site IV selectively inhibited either hemolysis or cell fusion. This finding may indicate that the fusion of the viral envelope with erythrocytes and host cell membrane is modulated through different ways. Comparative analysis of different NDV strains using monoclonal antibodies to each of the different antigenic sites showed that the antigenicity of the F protein is highly conserved.

Determination of the complete nucleotide sequence of the Sendai virus genome RNA and the predicted amino acid sequences of the F, HN and L proteins

We previously determined the 3' proximal 5,824 nucleotides of the Sendai virus genome RNA (Nucleic Acids Res. 11, 7317-7330, 1983; Nucleic Acids Res. 12, 7965-7973, 1984), and present here the sequence of the remaining 5' proximal 9,559 nucleotides. Thus, this is the first paramyxovirus to have its genome organization elucidated. The set of complementary DNA clones used was prepared by the method of Okayama and Berg from polyadenylylated viral genome RNA. We sequenced the region containing the 5' proximal half of the F gene, and the subsequent HN and L genes, and predicted the complete amino acid sequence of the products of these genes. Sequence analyses confirmed that all the genes are flanked by consensus sequences and suggest that the viral mRNAs are capable of forming stem-and-loop structures. Comparison of the F and HN glycoproteins of Sendai virus with those of simian virus 5 strongly suggests that the cysteine residues are highly important for maintenance of the molecular structures of these glycoproteins.

Human parainfluenza type 3 virus hemagglutinin-neuraminidase glycoprotein: nucleotide sequence of mRNA and limited amino acid sequence of the purified protein

The nucleotide sequence of mRNA for the hemagglutinin-neuraminidase (HN) protein of human parainfluenza type 3 virus obtained from the corresponding cDNA clone had a single long open reading frame encoding a putative protein of 64,254 daltons consisting of 572 amino acids. The deduced protein sequence was confirmed by limited N-terminal amino acid microsequencing of CNBr cleavage fragments of native HN that was purified by immunoprecipitation. The HN protein is moderately hydrophobic and has four potential sites (Asn-X-Ser/Thr) of N-glycosylation in the C-terminal half of the molecule. It is devoid of both the N-terminal signal sequence and the C-terminal membrane anchorage domain characteristic of the hemagglutinin of influenza virus and the fusion (F0) protein of the paramyxoviruses. Instead, it has a single prominent hydrophobic region capable of membrane insertion beginning at 32 residues from the N terminus. This N-terminal membrane insertion is similar to that of influenza virus neuraminidase and the recently reported structures of HN proteins of Sendai virus and simian virus 5.

Inhibition of the assembly of Newcastle disease virus by monensin

Monensin inhibits the intracellular transport of the glycoproteins of Newcastle disease virus between cis and trans Golgi stacks of infected BHK cells, as evidenced by its effect upon their post-translational modifications such as fatty acid acylation, glycosylation and proteolytic cleavage. Thus the drug has markedly altered the subcellular distribution of the glycoproteins so that they accumulate in the internal smooth membranes but are virtually absent in the plasma membrane. These glycoproteins that accumulated in intracellular membranes have a cytoplasmic domain susceptible to protease digestion and thus are transmembranous. Under such conditions, the behavior of M protein, which plays a crucial role in virus assembly (Y. Nagai et al., 1976, Virology 69, 523-538), has been analyzed. It has been found that the M protein can neither associate with the internal membranes nor bind to the plasma membrane. Thus no virus budding has been observed, either at the plasma membranes or at internal membranes. These results substantiate the view that the interaction between M and glycoproteins is of great importance for virus assembly and suggest further that this interaction is possibly only when the glycoproteins have been incorporated into the plasma membrane.

Expression at the cell surface of biologically active fusion and hemagglutinin/neuraminidase proteins of the paramyxovirus simian virus 5 from cloned cDNA

cDNAs encoding the mRNAs for the fusion protein (F) and the hemagglutinin/neuraminidase protein (HN) of the paramyxovirus simian virus 5 have been inserted into a eukaryotic expression vector under the control of the simian virus 40 late promoter. The F and HN proteins synthesized in recombinant infected cells are indistinguishable in terms of electrophoretic mobility and glycosylation from the proteins synthesized in simian virus 5-infected cells. In addition, the expressed F and HN proteins have been shown to be anchored in the plasma membrane in a biologically active form by indirect live cell immunofluorescence, the F-mediated formation of syncytia, and the ability of HN to cause the hemadsorption of erythrocytes to the infected cell surface.