Ribonucleic acid polymerase activity in Sendai virions and nucleocapsid

Viral RNA polymerases

Recent progress in molecular biological techniques revealed that genomes of animal viruses are complex in structure, for example, with respect to the chemical nature (DNA or RNA), strandedness (double or single), genetic sense (positive or negative), circularity (circle or linear), and so on. In agreement with this complexity in the genome structure, the modes of transcription and replication are various among virus families. The purpose of this article is to review and bring up to date the literature on viral RNA polymerases involved in transcription of animal DNA viruses and in both transcription and replication of RNA viruses. This review shows that the viral RNA polymerases are complex in both structure and function, being composed of multiple subunits and carrying multiple functions. The functions exposed seem to be controlled through structural interconversion.

Characterization of in vitro transcription and transcriptional products of measles virus

Ribonucleoprotein complexes isolated from measles virus-infected HeLa cells contained an RNA-dependent RNA polymerase activity that catalyzed the incorporation of ribonucleotides into ribonucleic acid. The ribonucleoprotein complexes were composed of measles virus nucleoprotein, phosphoprotein, and a large protein, as well as viral RNA. The kinetics of RNA synthesis at different temperatures, time intervals, and protein, ribonucleotide, and mono- and divalent cation concentrations were analyzed. Enzyme activity was maximum at 4 h at 25 degrees C in the presence of 100 mM Na+-2.5 mM Mg2+-1 mM ribonucleotides. Actinomycin D and alpha-amanitin had no effect on the enzyme activity. Addition of cytoplasmic extracts from uninfected HeLa cells to the reaction mixture did not increase the incorporation of ribonucleotides into RNA. The in vitro synthesized RNAs were characterize by slot blot analysis and quantitated by densitometer scanning. All mRNAs coding for the structural proteins of measles virus were synthesized. Nucleoprotein RNA was the most abundant species made, followed by phosphoprotein, hemagglutinin, fusion protein, matrix protein, and large-protein RNAs. The system described here resulted in the first efficient transcription of measles virus RNA and analysis of products.

Distinctive RNA transcriptase, polyadenylic acid polymerase, and polyuridylic acid polymerase activities associated with Pichinde virus

Three RNA polymerase activities were found and associated with purified Pichinde virus, a member of the Arenaviridae. A heat-labile polymerase activity which required all four ribonucleoside triphosphates for optimal activity co-sedimented on sucrose gradient centrifugation with the viral ribonucleoprotein complex from detergent-disrupted virus preparations. This enzyme synthesized heteropolymers which represented about 23% of the genome RNA as determined by nucleic acid hybridization. Two relatively heat-stable polymerase activities which differed in their cation requirement and substrate specificity were recovered with the virus-associated ribosomes. These polymerase activities synthesized homopolymers of limited chain length: in the presence of 10 mM Mg2%, polyuridylic acid was made, whereas in the presence of 1 mM Mn2%, polyadenylic acid was made. The addition of complementary RNA synthesized with the viral transcriptase in vitro to the reaction mixture containing the polyadenylic acid polymerase activity resulted in the terminal addition of polyadenylic acid to the complementary RNA. The possible function of the ribosome-associated polymerase activities in the replication of the virus is discussed.

Ends of the RNA within Sendai virus defective interfering nucleocapsids are not free

Sendai virus defective interfering nucleocapsids, isolated from infected cell cytoplasm by equilibrium banding in CsCl gradients, contain only the viral N protein. Neither end of the genomic RNA within these nucleocapsids is accessible to RNase digestion.

Transcriptase activity associated with rabies virion

Rabies virion-associated transcriptase activity was investigated in vitro and compared with that of the New Jersey serotype of vesicular stomatitis virus. The concentration of detergent that affected [3H]GMP incoporation into acid-insoluble material was significantly different for both viruses. Vesicular stomatitis virus New Jersey required 0.05 to 0.1% nonionic detergent, whereas rabies virion could not be fully activated unless 4 to 5% detergent was used. Other optimal conditions were as follows: 40 mM NaCl, 5 mM Mg2+, 40 mM Tris-hydrochloride (pH 7.4), 5 mM dithiothreitol, and 30 degrees C. The reaction required four nucleoside triphosphates. The initial rate of RNA synthesis by rabies virion enzyme was 140 pmol of GMP incorporated/mg of viral protein per h and linearly increased until about 8 h, with a slight initial lag phase. The enzyme activity that correlated with the content of L protein was highest when rabies virions were grown at 33 degrees C. The product was single-stranded RNA, which was complementary in base sequences to rabies viral RNA. Most of the RNA synthesized sedimented at 6-16S.

Measles virus and its associated diseases

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Joint recognition by cytotoxic T cells of inactivated Sendai virus and products of the major histocompatibility complex

Cytotoxic T cells specific for Sendai virus were generated by culturing murine spleen cells in vitro together with UV-inactivated Sendai virus. In vivo immunization of donor mice with UV-inactivated Sendai virus resulted in an in vitro secondary response of increased magnitude. Cytotoxic activity was demonstrated in a short-term 51Cr-release assay, using syngeneic tumor cells which had been coated with inactivated Sendai virus by incubation at 4 degrees C for 30 min. The lysis of Sendai virus-coated target cells was restricted by the H-2 haplotype of the target cells, suggesting that the H-2 genes of the target cell contributed to the specificity of the lysis. Kinetic experiments showed that susceptibility to lysis by cytotoxic T cells specific for Sendai virus appeared within 30 min after coating target cells with inactivated virus. Furthermore, there was no detectable synthesis of new proteins in cells treated with UV-inactivated Sendai virus. For these reasons, we suggest that neither viral replication nor the synthesis of new proteins are necessary for the production of the antigen recognized by cytotoxic cells specific for Sendai virus. We infer that the virus-specific component on the target cells is probably a preformed virion antigen adsorbed onto or integrated into the cell membrane. These results imply that, if the cytotoxic T cell recognizes a single antigenic determinant specified both by viral and H-2 genes, this determinant is formed by the physical association of H-2 and Sendai virus antigens rather than by their alteration during the processes of synthesis.

Isolation of a transcriptive complex from Newcastle disease virions

An active transcriptive complex was isolated from purified virions of Newcastle disease virus. After disruption with Triton X-100 and high salt, soluble and particulate fractions were separated by density gradient centrifugation. The transcriptive complex, recovered at a density of 1.275 g/cm3, appeared as a nucleocapsid structure by electron microscopy. When analyzed by polyacryl-amide gel electrophoresis, the nucleocapsids consisted of the nucleocapsid protein, a minor protein of 53,000 molecular weight, and the large L protein. Nucleocapsids possessed less than 1% of the hemagglutinating and neuraminidase activities originally associated with virions. The active complex synthesized predominantly 11 to 20S RNA in vitro and approximately one-fourth of the RNA molecules contained polyadenylic acid segments. In the presence of S-adenosyl-L-methionine, the RNA molecules were capped and methylated at the 5' termini. The transcriptive complex was also capable of methylating exogenous Escherichia coli RNA in the absence of viral RNA synthesis.

Synthesis of complementary RNA containing polyadenylic acid by Sendai virions in vitro

Sendai virus synthesized, in vitro, [32P]AMP- and [3H]AMP-labeled RNA that ranged in size from 3 to 25S with major peaks at 7S and 13S. Both labeled products were predominantly single-stranded RNA and were complementary in base sequence to 50S virion RNA. Passage of the 3 to 25S in vitro RNA transcripts through a polyuridylic acid-cellulose column revealed that only the larger (predominantly 18S) RNA transcripts contained polyadenylic acid[poly(A)] segments capable of binding to the column. After treatment with a combination of RNase A and T1, the majority of the in vitro poly(A) sedimented at 6S although the product ranged in size from 3 to 9S. Proof that the RNase-resistant material was indeed poly(A) was obtained by nearest-neighbor analysis when 95% of the radioactivity was recovered in AMP.

RNA polymerase in mumps virion

Mumps virions of the Enders' strain were examined for polymerase activity in vitro. An RNA-dependent RNA polymerase was found to be associated with the virion. The general properties of the reaction appear to be similar to those described for other paramyxoviruses.

Polymerase activity of Pichinde virus

Pichinde virus, a member of the arenavirus group, was examined for polymerase activity. Purified virus was found to contain RNA-dependent RNA polymerase but not RNA-dependent DNA polymerase activity. Since RNase but neither DNase nor actinomycin D inhibited the endogenous polymerase reaction, RNA of the virus appeared to be used as the template. The divalent cations Mg(2+) and Mn(2+) were required for optimal reactivity. The RNA product was partially resistant to RNase and the resistant portion had a sedimentation coefficient of 22 to 26S in sucrose gradients.

Sendai virion transcriptase complex: polyeptide composition and inhibition by virion envelope proteins

Sendai virions, disrupted in 2% Triton X-100 in 1 M KCl, were separated into nucleocapsids and envelope proteins by centrifugation. The nucleocapsids, representing 46% of the virion proteins, had a buoyant density of 1.29 gm/cm(3) in D(2)O sucrose. RNA-dependent transcriptase activity associated with them had a ninefold greater specific activity than transcriptase assayed in unfractionated detergent-disrupted virions. These enzyme-active nucleocapsids contained only two polypeptides, the largest virion polypeptide (molecular weight 75,000) and the nucleocapsid structure unit (molecular weight 60,000). Virion envelope proteins, either glycoproteins or nonglycosylated matrix protein, inhibited nucleocapsid-associated polymerase activity; brief heat denaturation abolished their inhibitory activity. Yeast RNA stimulated nucleocapsid-associated enzyme, suggesting that stimulatory polyanions act at the enzyme-template level.

Isolation of a ribonucleoprotein structure from oncornaviruses

Detergent treatment releases from both avian and mammalian oncornaviruses a structure containing the viral RNA and a major arginine-rich protein, as well as reverse transcriptase activity.

Cell-free translation of paramyxovirus messenger RNA

Polypeptides corresponding in electrophoretic mobility to virion polypeptides 1, 3, and 5 were made in a reticulocyte cell-free system to which 18S RNA from Sendai virus-infected cells was added. Immune precipitation was used to select relevant polypeptides from endogenous products. The cell-free product corresponding to virion polypeptide 3 (the nucleocapsid structure unit) was the most abundant; its tryptic peptides comigrated electrophoretically with tryptic peptides of polypeptide 3 isolated from virions. Other sedimenting classes of RNA from infected cells were tested; only the 28S fraction showed slight activity. Virion 50S RNA was inactive. These findings support the hypothesis that complementary RNA transcripts of paramyxovirion RNA are the templates for viral proteins.

Early events in cell-animal virus interactions

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Stimulation of Sendai virion transcriptase by polyanions

Exogenous polyribonucleotides stimulated the ribonucleic acid (RNA) transcriptase in Sendai virions. Added yeast RNA, polyadenylic acid, or polycytidylic acid increased incorporation of (3)H-guanosine monophosphate as much as fivefold. The products of stimulated reactions were virus-specific as determined by hybridization with Sendai virion RNA, but they sedimented more slowly (13s) than the product of an unstimulated reaction (16s). The stimulating activity was nondialyzable and heat stable, but was abolished by alkaline hydrolysis. Nucleoside monophosphates, individually or in combination, were ineffective, confirming the requirement for a polymer. Among other substances tested for effects on Sendai virion transcriptase, polyaspartic acid and polyglutamic acid stimulated the enzyme; polyinosinic acid, polyuridylic acid, and polyamines had no effect; and dextran sulfate and polyvinyl sulfate were inhibitory.

Measles virus ribonucleic acid and protein synthesis: effects of 6-azauridine and cycloheximide on viral replication

Cycloheximide and 6-azauridine were employed to study the time course of measles virus protein and nucleic acid syntheses in AV3 cells. Synthesis of ribonucleic acid (RNA) essential for infectivity was first detected at 6 hr and increased concurrently with the formation of essential protein. Maximum levels of virus-specific RNA and protein were present by 18 hr, a time when only 5% of progeny virus was detected. Essential RNA and protein syntheses preceded the formation of infectious virus by at least 10 to 12 hr. The time course of RNA and protein syntheses essential for the formation of complement-fixing (CF) antigen and salt-dependent agglutinin (SDA) was also determined. RNA synthesis essential for the formation of SDA was first detected at 2 hr and was present maximally by 6 hr, whereas SDA-protein increased concurrently with the protein essential for infectivity. This suggested that the last protein essential for infectivity may be SDA. RNA synthesis essential for the formation of CF antigen was first detected at 4 hr, while CF-protein increased at 5 hr and preceded SDA-protein and protein essential for infectivity by approximately 3 hr. Reversal of inhibition of protein synthesis by cycloheximide indicated that early protein synthesis (1 to 3 hr) was required for the formation of infectious virus. The data suggest that the relatively long eclipse period observed with measles virus is related to a long maturation period rather than to late formation of early proteins, viral RNA, or structural proteins.

Sendai virus-induced transcriptase from infected cells: polypeptides in the transcriptive complex

A Sendai virus-induced transcriptase-template complex was isolated from the cytoplasm of infected cells by combined sedimentation and isopycnic centrifugation. This transcriptive complex banded at 1.27 g/cm(3) in D(2)O-sucrose gradients. It contained two polypeptides, the viral nucleocapsid structure unit (molecular weight, 60,000) and the largest virion polypeptide (molecular weight, 75,000). The buoyant density, chemical composition, and electron microscopic appearance of the transcriptive complex indicate a structure like that of viral nucleocapsids.

Transfer ribonucleic acid nucleotidyltransferase and transfer ribonucleic acid in Sendai virions

Sendai virions contain both transfer ribonucleic acid (tRNA) nucleotidyltransferase and its substrate, tRNA missing its CCA-OH end.

Degradation of single- and double-stranded RNA by frog virus 3

Purified preparations of frog virus 3 possess ribonuclease activities directed against single-and double-stranded RNA. Double-stranded RNAs isolated from purified reovirus type 3 and from HeLa cells infected with poliovirus and single-stranded poliovirus RNA from purified virus are readily degraded by incubation with frog virus 3. The mode of action of the nucleases is endonucleolytic. Under the assay conditions used for the viral enzyme, crude extracts of uninfected HeLa, L, and baby hamster kidney cells did not show enzyme activity against double-stranded RNA but exhibited activity against single-stranded RNA. The dependence of the viral nucleases on divalent cations for optimal activity and the inhibition of the cleavage of single-stranded RNA by 0.2 M NaCl suggests that the enzymes are either virus-coded or virus-induced.

Relationship between the ribonucleic acid synthesizing capacity of ultraviolet-irradiated Newcastle disease virus and its ability to induce interferon

Ultraviolet (UV)-irradiated Newcastle disease virus which has lost its infectivity but has the capacity to induce interferon also has the capacity to induce ribonucleic acid (RNA) synthesis both in vitro and early in infection in vivo. With large doses of UV irradiation, RNA-synthesizing capacity and interferon-inducing capacity are lost in parallel. Limited amounts of base-paired RNA associated with a transcriptive intermediate are involved in this RNA synthesis. These findings suggest the possibility that the single-stranded RNA of the UV-irradiated virus induces interferon by serving as a template for the synthesis of base-paired RNA. UV irradiation of the virus breaks down viral RNA but at a rate which is too slow to be a major cause of the loss of RNA-synthesizing capacity. Evidence is presented which suggests that less of the template RNA of the UV-irradiated virus is copied and that the product which is synthesized is smaller than that synthesized by nonirradiated virus.

Effect of -propiolactone on Sendai virus

The biological properties (infectivity, hemagglutination, hemolysis, cell fusion, neuraminidase) of Sendai virus were dissociated on the basis of sensitivity to beta-propiolactone, by freeze-thawing, by heating at different temperatures, and by adsorption-elution with formalinized chicken erythrocytes. Possible mechanisms whereby beta-propiolactone selectively destroys viral infectivity are discussed.