Polyadenylation of vesicular stomatitis virus mRNA

Alternate capping mechanisms for transcription of spring viremia of carp virus: evidence for independent mRNA initiation

Two alternate mechanisms of mRNA capping for spring viremia of carp virus have been observed. Under normal reaction conditions, a ppG residue of the capping GTP is transferred to a pA moiety of the 5' termini of mRNA transcripts. However, in reaction conditions where GppNHp is used instead of GTP, an alternate capping mechanism occurs whereby a pG residue of the capping GTP is transferred to a ppA moiety of the transcripts. The first mechanism is identical to that described previously for vesicular stomatitis virus (G. Abraham, D. P. Rhodes, and A. K. Banerjee, Nature [London] 255:37-40, 1975; A. K. Banerjee, S. A. Moyer, and D. P. Rhodes, Virology 61:547-558, 1974), and thus appears to be a conserved function during the evolution of rhabdoviruses. The alternate mechanism of capping indicates not only that capping can take place by two procedures, but also that the substrate termini have di- or triphosphate 5' ends, indicating that they are probably independently initiated. An analog of ATP, AppNHp, has been found to completely inhibit the initiation of transcription by spring viremia of carp virus, suggesting that a cleavage between the beta and gamma phosphates of ATP is essential for the initiation of transcription. However, in the presence of GppNHp, uncapped (ppAp and pppAp), capped (GpppAp), and capped methylated (m7GpppAmpAp and GpppAmpAp) transcripts are detected. Size analyses of oligodeoxythymidylic acid-cellulose-bound transcripts resolved by formamide gel electrophoresis demonstrated that full-size mRNA transcripts are synthesized as well as larger RNA species. The presence of GppNHp and S-adenosylhomocysteine in reaction mixtures did not have any effect on the type of unmethylated transcription products. Our results favor a transcription model postulated previously (D. H. L. Bishop, in H. Fraenkel-Conrat and R. R. Wagner, ed., Comprehensive Virology, vol. 10, Plenum Press, New York, 1977; D. H. L. Bishop and A. Flamand, in D. C. Burke and W. C. Russell, ed., Control Processes in Virus Multiplication, Cambridge University Press, Cambridge, 1975; D. H. L. Bishop and M. S. Smith, in D. Nayak, ed., The Molecular Biology of Animal Viruses, Marcel Dekker, New York, 1977; P. Roy and D. H. L. Bishop, J. Virol. 11:487-501, 1973) in which mRNA synthesis is initiated independently; they do not support a model for transcripts being synthesized by plus-strand cleavage (A. K. Banerjee, G. Abraham, and R. J. Colonno, J. Gen. Virol. 34:1-8, 1977; A. K. Banerjee, R. J. Colonno, D. Testa, and M. T. Franze-Fernandez, in B. M. J. Mahy and R. D. Barry, ed., Negative Strand Viruses and the Host Cells, Academic Press, London, 1978).

Effect of cordycepin triphosphate on in vitro RNA synthesis by plant viral replicases

In vitro RNA synthesis by tobacco mosaic virus and cowpea chlorotic mottle virus replicase were inhibited by cordycepin triphosphate. Inhibition could be overcome with higher concentrations of ATP in assay mixtures but not with UTP. Products synthesized in vitro by tobacco mosaic virus RNA replicase in the presence of inhibitor revealed replicative form but not replicative intermediate RNAs. These results suggest that cordycepin triphosphate competes specifically with ATP and results in premature termination of viral RNA synthesis in vitro.

Modulation of production of hepatitis B surface antigen by a human hepatoma cell line

Three drugs were assayed for their capacity to inhibit hepatitis B surface antigen (HBsAg) production by the PLC/PRF/5 human hepatoma cell line. The effect on cell growth and HBsAg production of Cordycepin, 6-azauridine, and Hygromicin B is reported. Hygromicin B, a translation inhibitor unable to penetrate normal cells, greatly reduced HBsAg production by growing and confluent cells.

Effect of cordycepin triphosphate on in vitro RNA synthesis by picornavirus polymerase complexes

Cordycepin triphosphate inhibited in vitro [3H]GMP incorporation by pricornavirus-specific polymerase complexes isolated from infected HeLa cells. The inhibition of [3H]GMP incorporation could be reversed with ATP added to the reaction mixture along with the inhibitor, but not with GTP so added or with ATP added 10 min after the inhibitor. Products synthesized in vitro in the presence of cordycepin triphosphate lacked full-length single-stranded viral RNA. These results support RNA chain termination by specific competition with ATP as the mechanism of inhibition of picornavirus-specific RNA synthesis by cordycepin triphosphate.

The effect of cordycepin on the multiplication of Semliki Forest virus and on polyadenylation of viral RNA

Cordycepin (3'-deoxyadenosine), at a concentration of 20 microgram/ml, has a marked effect on Semliki Forest virus multiplication. The appearance of plaque forming units is delayed by about 2 hours and the yield greatly reduced. The incorporation of [3H] uridine into intracellular viral RNAs reaches less than 50 per cent of controls. However, no specific effect on poly (A) synthesis could be detected. The binding efficiency of viral RNAs on nitrocellulose membranes and poly (U) sepharose is not affected by cordycepin. The average poly (A) length of total intracellular viral RNA was calculated on the basis of the ratio of the radioactivity of adenosine-monophosphate: adenosine and found to be about 35 nucleotides in treated and untreated cells.

Effect of cordycepin on the replication of western equine encephalitis virus

Cordycepin (3'-deoxyadenosine) inhibited viral RNA synthesis in the replication of western equine encephalitis virus, thereby causing a reduction of virus production. The rate of inhibition of viral RNA synthesis was dependent on drug concentration and the period of treatment with the drug. These results suggest that the virus RNA synthesizing system is sensitive to the drug.

Polyadenylate sequences of human rhinovirus and poliovirus RNA and cordycepin sensitivity of virus replication

The polyadenylate [poly(A)] content of the genome RNA of human rhinovirus type 14 (HRV-14) is nearly twice as large as that of the genome RNA of poliovirus type 2. The poly(A) content of viral RNA was determined to be the RNase-resistant fraction of 32P-labeled viral RNA extracted from purified virions. Polyacrylamide gel electrophoresis indicated that the poly(A) sequences of HRV-14 are more heterogenous and on an average larger than those of poliovirus RNA. On the basis of susceptibility to micrococcal polynucleotide phosphorylase the rhinovirus genome terminates in poly(A). Replication of both viruses is almost totally inhibited by cordycepin at 50 mug/ml. At lower concentrations, rhinovirus replication is more sensitive to cordycepin than poliovirus replication. Addition of cordycepin (75 mug/ml) to infected culture prior to or during viral RNA replication results in more or less complete inhibition of virus-specific RNA synthesis. The results do not indicate that cordycepin sensitivity of either virus is due to preferential inhibition of viral poly(A) synthesis by this antibiotic.

Newcastle disease virus-specific RNA: poly(A)-containing and poly(A)-deficient transcripts as revealed by chromatography on poly(U)-sepharose

Total [3H]uridine-labeled, virus-specific RNA from Newcastle disease virus-infected cells was fractionated by poly(U)-sepharose chromatography and analyzed by rate zonal gradient centrifugation. The sedimentation pattern of both eluted and nonadsorbed RNA resembled that of the total RNA. However, nonadsorbed RNA was enriched in 50S material, ant its 18S peak was broader and slightly shifted towards the top of the gradient. Poly(U-sepharose chromatography of isolated 18S RNA and 24S RNA resulted in the separation of poly(A)-containing RNA and poly(A)-deficient RNA. In the former the percentage of adenosine content represented by poly(A) sequences was estimated as 10 to 12% (for 18S RNA) or approximately 6.0% (for 24S RNA). The size of poly(A) fragments as measured by their sedimentation rate was the same for 18S and 24S RNA. Polyacrylamide gel electrophoresis of poly(A)-containing RNA revealed a characteristic pattern closely resembling the pattern of nonchromatographed 18S and 24S RNA. The pattern of poly(A)-deficient RNA was heterogenous, and for 18S RNA it shifted towards the anode. The possible origin of poly(A)-deficient transcripts is discussed.

The sensitivity of RNA polymerases I and II from Novikoff hepatoma (N1S1) cells to 3'-deoxyadenosine 5'-triphosphate

The synthesis of ribosomal precursor RNA in Novikoff hepatoma (N1S1) cells is very sensitive to cordycepin (3'-dA). The synthesis of hnRNA, however, is resistant to inhibition concentrations of 3'-dA that completely block the synthesis of 45S ribosomal RNA precursor. We have examined the RNA polymerases present in these cultured cells with regard to their sensitivity to cordycepin 5'-triphosphate (3'-dATP) in an effort to explain the differential inhibition of RNA synthesis observed in vivo. RNA polymerases I and II were characterized on the basis of their chromatographic behavior on DEAE-Sephadex, as well as the response of their enzymatic activities to ionic strength, the divalent metal ions Mn2+ and Mg2+, and the toxin alpha-amanitin. For both enzymes the inhibition of in vitro RNA synthesis by 3'-dATP was competitive for ATP. The km values for ATP and the K1 values for 3'-dATP for the two enzymes were quite similar. RNA polymerase II, the enzyme presumed responsible for hnRNA synthesis, was actually slightly more sensitive to 3'-dATP than RNA polymerase I, the enzyme presumed responsible for ribosomal precursor RNA synthesis. Similar data were obtained when the RNA polymerases were assayed in isolated nuclei. These results indicate that the differential inhibition of RNA synthesis caused by 3'-dA in vivo cannot be simply explained by differential sensitivity of RNA polymerases I and II to 3'-dATP.

5'-terminal sequence of vesicular stomatitis virus mRNA's synthesized in vitro

Unmethylated or methylated 12 to 18S mRNA's synthesized in vitro by the virion-associated RNA polymerase of vesicular stomatitis virus contain the 5'-terminal hexanucleotide sequence G(5')ppp(5')ApApCpApGp...or m 7G(5')-ppp(5')ApmApCpApGp..., respectively. The implication of these results in relation to the regulation of transcription in vesicular stomatitis virus is discussed.

Effect of cordycepin (3'-deoxyadenosine) on virus-specific RNA species synthesized in Newcastle disease virus-infected cells

Cordycepin (3'-deoxyadenosine) has no effect on the size or relative proportions of Newcastle disease virus-specific 18-22S mRNA species nor on the amount or size of the polyadenylic acid associated with them. Cordycepin does, however, cause an inhibition of incorporation of [3H]uridine into 50S virus-specific RNA relative to 18-22S RNA. This inhibition is probably not a direct effect of the drug on the synthesis of 50S viral RNA. Like cycloheximide, another drug which inhibits 50S RNA accumulation in paramyxovirus-infected cells, cordycepin inhibits protein synthesis as measured by amino acid incorporation. It is likely that the inhibition of 50S RNA accumulation is a secondary effect of protein synthesis inhibition. This is supported by the finding that concentrations of cordycepin and cycloheximide, which inhibit protein synthesis to the same extent, have the same effect on the ratio of 50 to 18-22S virus-specific RNA.

Replication of picornaviruses. I. Evidence from in vitro RNA synthesis that poly(A) of the poliovirus genome is genetically coded

A crude replication complex has been isolated from poliovirus-infected HeLa cells and used for synthesis of poliovirus replicative intermediate (RI) RNA, replicative form (RF) RNA, and single-stranded (SS) RNA in vitro. All three classes of virus-specific RNA synthesized in vitro are shown to contain poly(A). Poly(A) of RF and of SS RNA [RF-poly(A) and SS-poly(A)] has a chain length (50 to 70 nucleotides) that is shorter than that of poly(A) of in vivo-synthesized RNAs. Poly(A) of RI [RI-poly(A),] however, is at least 200 nucleotides long and, therefore, larger than poly(A) of RI isolated from HeLa cells 4 h after infection. The crude membrane-bound replication complex contains a terminal adenylate transferase activity that is stimulated by Mn2+ and the addition of an (Ap)2AOH primer. This transferase activity is found also in extracts of mock-infected cells. Partial purificaiton of the replication complex in a stepwise sucrose gradient, in which the viral replicase is associated with the smooth cytoplasmic membrane fraction, does not remove the terminal transferase. However, when the partially purified replication complex is treated with deoxycholate and sedimented through a sucrose gradient, a soluble replication complex can be isolated that is free from terminal adenylate transferase. This soluble replication complex was found to synthesize viral RNA-linked poly(A) longer in chain length than that synthesized by the crude replication complex. Taking into account the 5'-terminal poly(U) in poliovirus minus strands, our data suggest that polyadenylation of poliovirus RNA occurs by transcription and not by end addition. When compared to other viral systems, poliovirus and, probably, all picornaviruses appear to be unique in that the poly(A) of their genome is genetically coded.

Both NS and L proteins are required for in vitro RNA synthesis by vesicular stomatitis virus

Vesicular stomatitis virions, Indiana serotype, were solubilized with high salt solubilizer and separated by ultracentrifugation into a supernatant fraction containing L, G, NS, and M proteins and pellet fraction containing the RNA complexed with N protein. NS protein was purified from the supernatnat fluid by sequential chromatography on phosphocellulose and diethylaminoethyl cellulose columns. The purified NS protein was assayed in a standard transcription system in combination with purified L protein and purified template (pellet fraction) prepared by renografin or CsCl banding. Results of the polymerase assays indicate that both L and NS proteins are required to reconstitute transcription activity with a highly purified template composed of only RNA and N protein. The NS protein polymerase activity is destroyed by trypsin but withstands 90 C temperatures for 10 min. Cytoplasmic NS protein can substitute for virion NS protein in the in vitro transcription assay.