Protamine--a potent inhibitor of vesicular stomatitis virus transcriptase in vitro

Sequential phosphorylation of the phosphoprotein of vesicular stomatitis virus by cellular and viral protein kinases is essential for transcription activation

The phosphoprotein (P) and the large protein (L) constitute the RNA-dependent RNA polymerase of vesicular stomatitis virus (VSV). We show that phosphate-free P protein expressed in bacteria is transcriptionally inactive when reconstituted with L protein and viral N-RNA template free of cellular protein kinase. Phosphorylation of P protein by a cellular kinase(s) was essential for transcription as well as for further phosphorylation by an L-associated kinase, the two kinases acting in a sequential (cascade) manner. Phosphate groups introduced by cell kinase were stable, whereas those due to L kinase underwent a turnover which was coupled to ongoing transcription. We present a model for the phosphorylation pathway of P protein and propose that continued phosphorylation and dephosphorylation of P protein may represent a transcriptional regulatory (on-off) switch of nonsegmented negative-strand RNA viruses.

Influence of polyions on the early steps of enterovirus infection

The influence of electric charged molecules on the early phases of enterovirus infection was studied in order to select antiviral compounds able to prevent viral attachment. The effect of different polyelectrolytes on the multiplication of coxsackie virus B3, echovirus 6 and hepatitis A virus was investigated in susceptible cells by adding the drug before, during or after the viral adsorption period. Among polyanions, the polysaccharides heparin and dextran sulfate inhibited viral infectivity, dextran sulfate being the most effective mainly towards hepatitis A virus infection. DEAE-dextran and protamine sulfate, generally recognized as enhancers of infectivity of naked and enveloped viruses, exhibited an inhibitory effect towards the three picornaviruses tested. Only in the case of hepatitis A did DEAE-dextran slightly improve viral antigen synthesis. The inhibitory effect shown by compounds belonging to positive and negative polyions suggests that the electric charge is not sufficient by itself to explain the antiviral activity of these drugs.

Inhibitory effects of atropine, protamine, and their combination on hepatitis A virus replication in PLC/PRF/5 cells

Atropine, protamine, and the combination of these drugs were tested for their effects on hepatitis A virus (HAV) replication in cell culture. PLC/PRF/5 hepatoma cells were treated simultaneously with nontoxic concentrations of these drugs and inoculated with HAV strain CF 53 at several multiplicities of infection. The yields of infectious HAV after 4 and 15 days were markedly reduced by each drug, especially at the lowest multiplicity of infection. The activities of each drug were irreversible. Atropine was active when it was added as late as 2 h after inoculation with HAV. An anti-HAV effect was also induced by treating cells with atropine prior to inoculation. Protamine was active as late as 6 h postinoculation. The combination of atropine and protamine resulted in an enhanced anti-HAV effect. We concluded that these drugs affect undetermined, but separate, steps in the HAV replication cycle.

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.

Phosphorylation within a specific domain of the phosphoprotein of vesicular stomatitis virus regulates transcription in vitro

We have investigated the functional significance of phosphoserine residues that lie in the L protein-binding domain between amino acids 213 and 247 of the phosphoprotein (NS) of vesicular stomatitis virus. A series of mutant NS proteins were made by cell-free translation of mRNAs transcribed from the cloned gene. Site-directed substitution of alanine for both serine 236 and serine 242 essentially abolished RNA synthesis catalyzed by the NS-L complex. Substitution of either of these serines reduced RNA synthesis by 75%. Serine 218 played no major role in RNA synthesis. Phosphorylation of NS by the L protein was abrogated by substitution of either serine 236 or serine 242. These results indicate that phosphorylation of serines 236 and 242 in the NS protein regulates its binding with the L protein and the N-RNA template and is essential for activation of viral RNA synthesis.

Effect of antiviral substances on hepatitis A virus replication in vitro

The effect of protamine, atropine, selenocystamine, taxifolin, and catechin on the infectivity and antigenicity of the cell culture-adapted hepatitis A virus (HAV) strain CF 53 was studied. The toxicity on uninfected PLC/PRF/5 cells was examined for each antiviral compound by morphological and biochemical methods, in order to determine concentrations without cytotoxic effect. At these concentrations, protamine and taxifolin, added to infected cells for a 15-day period, caused concentration-dependent reductions in the infectivity and antigenicity of HAV. Atropine also caused a concentration-dependent reduction of HAV infectivity but did not affect the antigenicity of the virus. At the highest concentration used, 50 micrograms/ml of protamine, 59 micrograms/ml of taxifolin, and 50 micrograms/ml of atropine, the infectious viral titer reduction was 1.56, 0.77, and 0.68 log10, respectively. Selenocystamine and catechin had no effect on HAV replication.

Identification of a domain within the phosphoprotein of vesicular stomatitis virus that is essential for transcription in vitro

A full-length cDNA copy of the phosphoprotein (NS) mRNA of vesicular stomatitis virus (New Jersey serotype) was inserted into pGEM4 vector downstream of the promoter for bacteriophage SP6 RNA polymerase. Transcription of the cDNA in vitro resulted in the synthesis of NS mRNA, which was subsequently translated into NS protein in a cell-free rabbit reticulocyte system. The biological activity of the expressed NS protein was demonstrated by in vitro synthesis of mRNA by transcription-reconstitution with purified viral L protein and N-RNA template. Deletion mapping of the NS gene defined a specific domain between amino acid residues 213 and 247, which was essential for in vitro transcription. Removal of the COOH-terminal 21 amino acids, on the other hand, did not have a significant effect on transcription. This domain appears to be involved in efficient binding of NS protein to the N protein-RNA template.

Phosphoprotein NS of vesicular stomatitis virus: phosphorylated states and transcriptional activities of intracellular and virion forms

The phosphorylation and transcriptional competence of the free cytoplasmic form and the virion form of NS protein of vesicular stomatitis virus (VSV-Indiana/Mudd-Summers) were compared. NS protein is known to exist in two distinct phosphorylated states, NS1 and NS2, that are resolvable by gel electrophoresis. In vitro phosphorylation of virion NS protein by the viral L protein-associated protein kinase resulted in the phosphorylation of both NS1 and NS2. However, in the presence of the N-RNA complex, the NS2 form was preferentially phosphorylated. A cellular protein kinase activity, found in cytoplasmic extracts from VSV-infected or uninfected cells, preferentially phosphorylated NS1, which did not undergo dephosphorylation by cellular phosphatase and also did not convert to NS2. In contrast, the virion or cellular NS2 which had been phosphorylated in vivo or in vitro could be rapidly dephosphorylated by a cellular phosphatase. Cytoplasmic NS protein was found to be fully capable of binding to the virion N-RNA template, and in conjunction with L protein, it participated in synthesis of the leader RNA and five mRNA species of VSV. Moreover, under these conditions, neither cellular phosphatase nor cellular ribonuclease was able to bind to reconstituted nucleocapsids. Binding of cytoplasmic NS to the virion N-RNA template in the presence of L protein resulted in a large and preferential enhancement of NS2 phosphorylation. A protein kinase activity, which phosphorylated NS protein in vitro, was found to be associated with the N-RNA template. This activity appeared to be very tightly bound to N-RNA and exhibited absolute specificity for NS protein of the homologous serotype.

Initiation of RNA synthesis in vitro by vesicular stomatitis virus: single internal initiation in the presence of aurintricarboxylic acid and vanadyl ribonucleoside complexes

In the presence of aurintricarboxylic acid (ATA) and vanadyl ribonucleoside complexes (VRC), we have isolated and characterized a small RNA, product of VSV in vitro transcription. This RNA is capped and lacks poly(A) at its 3'-end. Nucleotide sequence analysis revealed that this RNA corresponds to the 5'-terminal transcription product of the N-gene. The termination of the transcription occurs precisely at the 118th base from the 3'-end of the VSV genome. Analysis of the nucleotide sequence around this region reveals a potential secondary structure. Photoreaction of the VSV with 4'-substituted psoralen fails to inhibit the synthesis of the 68-mer RNA under conditions where full length mRNA synthesis is blocked, indicating that the psoralen binding site is located further into the N-gene. Since this RNA is the only in vitro transcription product synthesized under these conditions, the existence of two types of polymerase activities, one for the synthesis of leader RNA and one for mRNA, is suggested.