Synthesis in vitro of RNA complementary to parental viral RNA by RNA polymerase induced by influenza virus

Specific inhibition of the synthesis of influenza virus late proteins and stimulation of early, M2, and NS2 protein synthesis by 3-deazaadenosine

3-Deazaaristeromycin and 3-deazaadenosine (3DA-Ado) both interfere with the methylation of RNA, but only 3DA-Ado is metabolized to the corresponding homocysteine derivative. In contrast to 3-deazaaristeromycin, 3DA-Ado inhibits the synthesis of late influenza A virus proteins in chicken embryo cells (CEC), while it causes an overproduction of early proteins and of the nonstructural proteins NS2 and M2. Only the former effect of 3DA-Ado can be reversed by concomitant addition of adenosine, but not by guanosine. 3DA-Ado acts only early in the infectious cycle and, after removal of the drug, its effect on the yield of infectious virus is reversible. It can be significantly enhanced by homocysteine thiolactone. Except for the M gene, synthesis of viral mRNA is not significantly affected by 3DA-Ado. We conclude that 3DA-Ado acts via its homocysteine derivative by interfering with a specific post-transcriptional modification of viral mRNA and on splicing of specifically the M mRNA. In L-cells influenza viral protein synthesis is comparable to that in CEC in the presence of 3DA-Ado in that there is only little HA and M1 synthesized, and a severe overproduction of NS2 is observed. Under the experimental conditions 3DA-Ado has no inhibiting effect on the replication of other RNA viruses like Newcastle disease virus, Semliki Forest virus, or West Nile virus whose RNA is not methylated, since they do not have a nuclear phase during replication.

Mutants of an influenza A reassortant which are cold-sensitive (cs) as well as temperature-sensitive (ts): on the role of the neuraminidase activity for influenza virus infection

Temperature-sensitive (ts) mutants were obtained by undiluted passage of the cold-sensitive (cs) influenza A reassortant 113/Ho. This reassortant produces normal yields of infectious virus with negligible neuraminidase (NA) at 40 degrees. The mutants obtained from it had a narrow temperature optimum for plaque formation in chick embryo cells, since they were cs as well as ts. Such cs/ts mutants have not been described before. In contrast to mutants derived from FPV, most of the mutants derived from 113/Ho carried a ts defect in the NA gene. NA activity was not detectable after infection with these mutants at 40 degrees. The results are interpreted to mean that, although NA activity is not completely dispensible for influenza A virus replication in tissue cultures, the viruses possess a surplus of NA activity. The normally high activity of NA of influenza viruses seems to be necessary only for the natural infection of the respiratory tract.

A mutant of fowl plague virus (influenza A) with an altered glycosylation pattern in its hemagglutinin

A temperature-sensitive mutant (ts 1/1) with a defect in the hemagglutinin (HA) gene, which was obtained by undiluted passage of fowl plague virus (FPV) at 33 degrees, is described. At 33 degrees proteolytic cleavage of the abnormal HA yielded an altered HA2 (XHA2) which migrated ahead of the NS1 protein and lacked the complex oligosaccharide side chain. At the nonpermissive temperature of 40 degrees, the migration of the HA of ts 1/1 from the rough endoplasmic reticulum (RER) via the Golgi apparatus to the cell surface was rate limiting for virus maturation. The HA was only slowly cleaved and migrated during polyacrylamide gel electrophoresis ahead of the HA of wild type FPV. Some revertants of ts 1/1 exhibited the same protein pattern as the mutant, others resembled wild type FPV, while one revertant gave rise to a mixture of HA2 and XHA2 at 40 degrees. These results suggest that (1) the loss of the complex oligosaccharide side chain is not responsible for the ts phenotype, (2) the mutation is presumably not at the site where the oligosaccharide side chain is linked to the protein backbone, and (3) ts 1/1 presumably carries a mutation located in RNA segment 4, which by pseudoreversion (suppressor mutation) in the same gene leads to different ts+ phenotypes.

Host range mutants of an influenza A virus

Temperature-sensitive (ts) mutants of fowl plague virus with a ts-lesion in segment 1 (ts 3, polymerase 1 gene) or segment 2 (ts 90, transport gene) do not form plaques on MDCK cells at the permissive temperature, while the wild type and ts-mutants of other groups are able to do so. This property is correlated with the ts-lesion, since revertants for the ts-lesion of ts 3 and ts 90 again form plaques on MDCK cells. The block on MDCK cells--at least for ts3--may be located in a late function, since viral RNA polymerase and hemagglutinin are formed in almost normal yields. MDCK cells infected with ts 3 or ts 90 exhibit a retarded cytopathic effect at 33 degrees C, but no cytopathic effect at 39 degrees C, at which temperature the infected cells can be passaged and super-infected with the wild type strain. Cells surviving the infection with ts 90 at 33 degrees C sometimes grow out again to a normal monolayer. It is suggested that the spread of virus is inhibited under these conditions.

RNAs of influenza virus recombinants derived from parents of known virulence for man

Extensive use of recombinants made from A/PR/8/34 (H0N1) and wild, virulent H3N2 viruses as live influenza vaccines has provided a number of viruses of defined virulence for man. Clinical symptoms produced by these strains have ranged from febrile influenza to local coryzal symptoms or nil. A study was therefore made of the extent to which the PR8 genome had been incorporated into that of a number of the recombinants. By RNA--RNA hybridization it seemed that recombinants which had 55 per cent of greater homology with the PR8 parent were likely to conform an acceptable standard of attenuation. Those with lesser homology were frequently, but not always, clinically virulent. The technique seemed potentially useful, therefore, for screening PR8 live vaccine recombinants in vitro before giving them to volunteers.

Inhibition of influenza RNA synthesis by virazole (ribavirin)

Virazole (ribavirin) inhibits the RNA synthesis of an influenza A virus (fowl plague). Neither virion RNA nor complementary RNA are produced. Although the effect of virazole can be counteracted by guanosine the inhibitor does not interfere with the uptake or incorporation of labelled guanosine into chick embryo cells, nor does replacement of glucose by mannose amplify the effect of virazole. Thus virazole seems not to act via an interference with the GTP pool. Synthesis of Semliki Forest virus RNA is not affected by virazole.

Effect of tetraethyl thiuram disulfide (disulfiram) on the multiplication of enveloped viruses

Disulfiram at concentrations between 0.1 and 0.3 mM inhibits the multiplication of Semliki Forest virus (SFV), fowl plague virus (FPV), Newcastle disease virus (NDV), vesicular stomatitis virus (VSV), and pseudorabies virus (PRV), when administered 1 hour before and during adsorption. There is, however, no inhibition of virus multiplication, when the drug is added after adsorption onto chick embryo cells. Disulfiram interferes neither with the receptors of the virus nor of erythrocytes, and it does not prevent virus adsorption. Possibly an early step in virus multiplication is affected by disculfiram. Infected cells once treated with the drug recover after some time of incubation in an ingibitor-free medium. The inhibitory state can be maintained, however, if relatively low doses of disulfiram are present in the culture medium also after adsorption. Disulfiram has no effect on macromolecular synthesis of the host cells. It has, however, a marked affect on membrane function. While virus multiplication is readily inhibited by disulfiram when chick embryo or BHK cells were investigated, virus multiplication in HeLa cells is almost resestant against the action of disulfiram.

Cellular RNA and influenza-virion RNA are synthesized from different pyrimidine-nucleoside-triphosphate pools in chick-embryo cells

Chick embryo cells infected with an influenza A (fowl plague) virus have been labelled with (3H)-uridine for different lengths of time. Virion RNA and cellular RNA have been separated by specific hybridization with a surplus of unlabelled viral complementary RNA and RNase digestion. The ratio of the specific radioacticity in the UMP and CMP moieties of both types of RNA has been determined. Since the rate of approach to equilibrium of CMP to UMP labelling of both types of RNA is completely different it is concluded that cellular and virion RNA are synthesized using different pyrimidine nucleoside triphosphate pools.

Analysis of the in vitro product of an RNA-dependent RNA polymerase isolated from influenza virus-infected cells

The products synthesized in vitro by an RNA-dependent RNA polymerase isolated from influenza virus-infected BHK21-F cells were analyzed by velocity sedimentation, annealing techniques, and acrylamide-agarose gel electrophoresis. Approximately 50% of the RNA synthesized in vitro remains associated with the 50 to 70S ribonucleoprotein complex containing polymerase activity; the remainder of the RNA polymerase product sediments heterogeneously with a peak at 13S. At least 90% of the in vitro product hybridizes with virion RNA. If polypeptides are labeled early in the growth cycle, both the P and NP polypeptides are detected in the ribonucleoprotein complex by acrylamide gel electrophoresis. The results suggest that the polypeptide composition and the products of the cell-associated RNA polymerase are similar to those of the RNA transcriptase associated with influenza virus particles.

Inhibition of the multiplication of vesicular stomatitis and Newcastle disease virus by 2-deoxy-d-glucose

The production of infectious vesicular stomatitis (VSV) and Newcastle disease virus can be completely inhibited by 2-deoxy-d-glucose in pyruvate-containing medium, if virus either grown in pyruvate-containing medium or dialyzed against phosphate-buffered saline is used for infection. Under these conditions, the synthesis of all VSV proteins is reduced. VSV RNA, which is synthesized at reduced rates, seems to be unstable. The effect is completely reversible. If virus grown in glucose-containing medium is used for infection, the production of both viruses is not significantly inhibited by 2-deoxy-d-glucose. Under these conditions the production of the VSV glycoprotein is specifically impaired, but does not lead to a marked reduction of the yield of infectious virus.

RNA-dependent RNA polymerase in nuclei of cells infected with influenza virus

Nuclei purified from chicken embryo fibroblast cells infected with influenza (fowl plague) virus contain an RNA-dependent RNA polymerase. The in vitro activity of this enzyme is insensitive to actinomycin D, and is completely destroyed by preincubation with ribonuclease. Enzyme induction is prevented if cells are treated with actinomycin D or cycloheximide at the time of infection. RNA-dependent RNA polymerase activity increases rapidly in cell nuclei from 1 h postinfection, reaches a maximum at 3 to 4 h, then declines; a similar RNA polymerase activity in the microsomal cell fraction increases from 2 h postinfection and reaches a maximum at 5 to 6 h. The characteristics of the nuclear and microsomal enzymes in vitro are similar with respect to pH and divalent cation requirements. The in vitro products of enzyme activity present in the nuclear and microsomal fractions of cells infected for 3 and 5 h were characterized by sucrose density gradient analysis, and annealing to virion RNA. The microsomal RNA polymerase product contained 67 and 93% RNA complementary to virion RNA at 3 and 5 h, respectively; for the nuclear RNA polymerase product these values were 40% in each case.

RNA-dependent RNA polymerase activity associated with virions and subviral particles of myxoviruses

In vitro RNA synthesis is catalyzed by an enzyme found in purified virions of each of nine influenza strains tested. The extent of [(3)H]UTP incorporation observed is strain dependent, with an obligate requirement for Mn(2+) ions and RNA template. At least 30% of purified product RNA shows resistance to degradation by ribonuclease A and T1 before and after annealing with exogenous RNA from influenza virions.

In vitro product of a ribonucleic acid polymerase induced by influenza virus

The ribonucleic acid (RNA)-dependent RNA polymerase induced in the microsomal fraction of cells infected with influenza virus synthesized a mixture of single-and double-stranded RNA in vitro. The single-stranded RNA sedimented mainly in the 8S region on sucrose density gradients, with a smaller proportion of the RNA sedimenting at 18S. This sedimentation pattern corresponds closely to that of incomplete influenza virus RNA. The double-stranded RNA formed in vitro sedimented at 11S, but molecules which may be replicative intermediate, sedimenting at 14 to 20S, were also detected in the in vitro reaction product. Similar species of RNA were detected in vivo by pulse-labeling infected cells at the time of polymerase harvest, but the proportion of each RNA species was different, most of the RNA being single-stranded and sedimenting in the 18S region. An 11S double-stranded RNA was also synthesized in vivo. Pulse chase analysis of the double-stranded RNA synthesized in vitro showed that most is stable, and only a small proportion turns over during the reaction. A proportion of the RNA formed in vitro could be annealed to RNA formed in infected cells and to RNA extracted from purified virus.