In vitro RNA synthesis by infectious pancreatic necrosis virus-associated RNA polymerase

The presence of an RNA-dependent RNA polymerase was demonstrated in purified infectious pancreatic necrosis virus (IPNV). The enzyme was active in vitro without any pretreatment of the virus. Optimum activity was shown at 30 degrees C, pH 8 and in the presence of 6 mM-magnesium ions. Approx. 50% of the polymerase product remained associated with the dsRNA template of the virions. The remainder was found as extravirion ssRNA broken down to 5S to 7S fragments by virus-associated RNase(s). Although the addition of bentonite considerably reduced the amount of RNA synthesized, it protected the ssRNA product from degradation. This, in turn, permitted the synthesis of small amounts of ssRNA, which when analysed by sucrose gradient centrifugation or polyacrylamide gel electrophoresis behaved identically to the 24S single-stranded virus mRNA produced in infected cells. The virion polymerase was not stimulated by S-adenosyl-L-methionine or the addition of cellular or capped reovirus ssRNA. Several other modifications of the assay system were tried in an attempt to increase 24S RNA synthesis, but with little success. When [3H]uridine-labelled virus was used in the polymerase reaction, some labelled 24S ssRNA was obtained, indicating that in vitro transcription may proceed by a semi-conservative (displacement) mechanism.

The plus-strand leader RNA of VSV inhibits DNA-dependent transcription of adenovirus and SV40 genes in a soluble whole-cell extract

In an attempt to determine the mechanism (or mechanisms) by which vesicular stomatitis virus (VSV) kills cells, products of VSV transcription were tested in a cell-free system for their capacity to inhibit transcription of SV40 DNA and plasmids containing adenovirus late promoter and adenovirus-associated RNA genes. VSV RNA transcripts and other RNAs were compared for their capacity to suppress transcription of these DNA templates by RNA polymerases and cofactors present in the HeLa-cell extract system. Relatively low concentrations of the plus-strand leader RNA made in vitro from the 3' end of the wild-type VSV genome were found to inhibit initiation of transcription catalyzed by both RNA polymerase II and RNA polymerase III. Polyadenylated VSV messengers and other natural and synthetic RNAs also caused some inhibitory effects on in vitro transcription from DNA templates, but only at extremely high concentrations. Compared with the wild-type plus-strand RNA leader, the leader RNA synthesized in vitro by defective-interfering VSV showed only limited capacity to inhibit RNA synthesis on adenovirus and SV40 DNA templates and only at concentrations at least 30 times greater than that of the wild-type leader. The existence of nucleotide sequences in wild-type leader RNA, not present in defective-interfering leader RNA, that could recognize and block promoters, polymerases or protein cofactors is discussed.

Interferon induction and macrophage activation by a mycovirus double-stranded RNA/tobramycin complex following treatment with human serum

Double-stranded RNA (dsRNA) molecules, generally effective inducers of interferon (IFN), have a weak potency in man apparently because of the presence of a serum RNAase which quickly inactivates extracellular dsRNA. We have discovered that tobramycin, an aminoglycoside, protects Penicillium chrysogenum mycovirus dsRNA (PCMdsRNA) from the degradative action of the nuclease. Exposure of the dsRNA/tobramycin complex to human serum results in some degradation, but still permits the production of significantly high titers of IFN upon injection into mice. Intraperitoneal (i.p.) treatment of CFI mice with both dsRNA and dsRNA/tobramycin complex activated macrophages to inhibit the growth of P815 mastocytoma target cells. Following in vitro treatment with human serum, free dsRNA failed to activate peritoneal macrophages in vivo under conditions where this activity of dsRNA/tobramycin complex was retained. By varying the ratio of moles of tobramycin (as free base) to the moles of RNA phosphorous, toxicity can be minimized, while retaining the biologic activities of dsRNA.

Enhancement of viral RNA-induced interferon production of L cells treated with insulin and amphotericin B methyl ester

A study was initiated to develop a more efficient method of producing high-titered L cell interferon. The induction of interferon by viral infectious RNA could be augmented by pretreating the cell cultures with insulin and infecting in the presence of Amphotericin B methyl ester (AmBME). L cells were treated for 24 hr with different concentrations of insulin and then challenged with MM virus RNA suspended in a balanced salt solution with and without AmBME. The fluids were collected 48 hr after infection and assayed for interferon activity. Interferon production was markedly increased in insulin-treated cultures and that the increase was dose-dependent.

Suppression of murine retrovirus polypeptide termination: effect of amber suppressor tRNA on the cell-free translation of Rauscher murine leukemia virus, Moloney murine leukemia virus, and Moloney murine sarcoma virus 124 RNA

The effect of suppressor tRNA's on the cell-free translation of several leukemia and sarcoma virus RNAs was examined. Yeast amber suppressor tRNA (amber tRNA) enhanced the synthesis of the Rauscher murine leukemia virus and clone 1 Moloney murine leukemia virus Pr200(gag-pol) polypeptides by 10- to 45-fold, but at the same time depressed the synthesis of Rauscher murine leukemia virus Pr65(gag) and Moloney murine leukemia virus Pr63(gag). Under suppressor-minus conditions, Moloney murine leukemia virus Pr70(gag) was present as a closely spaced doublet. Amber tRNA stimulated the synthesis of the "upper" Moloney murine leukemia virus Pr70(gag) polypeptide. Yeast ochre suppressor tRNA appeared to be ineffective. Quantitative analyses of the kinetics of viral precursor polypeptide accumulation in the presence of amber tRNA showed that during linear protein synthesis, the increase in accumulated Moloney murine leukemia virus Pr200(gag-pol) coincided closely with the molar loss of Pr63(gag). Enhancement of Pr200(gag-pol) and Pr70(gag) by amber tRNA persisted in the presence of pactamycin, a drug which blocks the initiation of protein synthesis, thus arguing for the addition of amino acids to the C terminus of Pr63(gag) as the mechanism behind the amber tRNA effect. Moloney murine sarcoma virus 124 30S RNA was translated into four major polypeptides, Pr63(gag), P42, P38, and P23. In the presence of amber tRNA, a new polypeptide, Pr67(gag), appeared, whereas Pr63(gag) synthesis was decreased. Quantitative estimates indicated that for every 1 mol of Pr67(gag) which appeared, 1 mol of Pr63(gag) was lost.

Base composition of rubella virus RNA. Brief report

The base composition of 32P-labelled RNA of rubella virus was shown to be; Gp:31.1, Ap:21.9, Cp:34.3 and Up:12.8 per 100 nucleotides. The result demonstrates that the virus is distinct from other members of family Togaviridae in that it possesses RNA with relatively high contents of Gp and Cp, and low content of Up. Viral RNA adsorbed to oligo (dT)-cellulose column was shown to be infectious, whereas no infectivity of RNA appearing in the void volume was found. This may indicate that viral RNA needs to carry a minimal length of poly(A) to be infectious.

Spontaneous cytotoxicity of murine cells treated with the interferon inducers BRL 5907 and BRL 10739

The effects of the polyribonucleotide interferon inducers, BRL 5907 and BRL 10739, on the spontaneous cytotoxicity of CBA mouse cells towards the allogeneic lymphoma EL-4, were investigated. Intravenous administration of BRL 5907 and BRL 10739 increased the cytotoxic activity of a non-adherent, theta-negative, surface immunoglobulin-negative cell present in the spleen, but had no effect on cells in the lymph nodes. Spleen cell cytotoxicity was established within 24 h of injection of the polyribonucleotides, but had disappeared by 4 days. In addition, injection of mice with BRL 10739 increased the spontaneous cytotoxicity of a nylon-wool-adherent, theta-positive spleen cell. Intraperitoneal injection of mice with BRL 5907 and BRL 10739 also enhanced the cytotoxic activity of a non-adherent peritoneal exudate cell.

Infective substructures of measles virus from acutely and persistently infected cells

Ribonucleoprotein from cells acutely or persistently infected with measles virus were shown to be infectious by the calcium phosphate technique. Very little or no infectivity was obtained when calcium phosphate precipitation was omitted. Electron microscopy showed that the majority of ribonucleoprotein structures isolated from acutely infected cells were folded, whereas those from persistently infected cells were linear in appearance.

Antiviral activity of virus-like particles from Lentinus edodes (Shiitake). Brief report

Interferon (IF) induction and antiviral activity by purified spherical (S) or filamentous (F) virus-like particles and S-derived RNA was studied. A single administration of S particles prior to virus challenge reduced significantly the mortality of mice infected with western equine encephalitis (WEE) virus.

Interferon induction by viruses. II. Sindbis virus: interferon induction requires one-quarter of the genome--genes G and A

We have measured the amounts of interferon formed by chick cells 'aged' in vitro in response to different amounts of infectious wild-type Sindbis virus. Our results suggest that one plaque-forming unit is enough to induce maximum interferon formation. With higher m.o.i. the yield of interferon is less. To inactivate the interferon-inducing activity of Sindbis virus, four times more u.v.-radiation was needed than to inactivate the infectivity of the virus. This suggests that only 25% of the virus genome need be intact in order to induce interferon. Temperature-sensitive Sindbis virus mutants from the three RNA+ complementation groups, C. D and E, gave rise to interferon in chick cells incubated at a non-permissive temperature, Similarly, mutants from two of the RNA- groups, B and F, gave rise to interferon, but not mutants from groups G and A. We conclude that no pre-formed inducer of interferon is present in Sindbis virus. It appears, however, that genes G and A represent a special one-quarter of the genome which must be functional in order to synthesize an interferon-inducing moiety. We suggest that this moiety is a double-stranded RNA molecule formed after synthesis of a segment of RNA complementary to the genome.

[Comparative antiviral and interferonogenic activity of natural and synthetic interferon inducers in vitro and in vivo]

Biological activities of the RNA replicative form of phage f2, a natural interferon inductor and poly-I -- poly-C, a synthetic polyribonucleotide complex were studied comparatively. Differences in the comparative interferonogenic and antiviral activity of the inductors were as dependent on the type of the cell system. It was shown that DEAE-dextran increased the interferon-inducing activity of RFf2 in the cell culture by 4 to 8 times. The dynamics of the interferonogenic and antiviral activity of RFf2 in the L-929 cell culture was studied. Interferon appeared in the culture fluid in 6--8 hours and reached its maximum titers (128 IU50/ml) by the 24th hour, the maximum protection of the cells being also developed by the 12th--24th hour, reaching on an average 51 g PFU/ml. It was shown in the experiments with green marmosets that administration of RFf2 in the form of aerosol in a dose of 2.3 mg/kg induced interferon production in the blood serum the titers of which amounted to 80--160 IU50/ml 24 hours after the administration.

Long-term culture of guinea pig tongue cells: a suitable interferon system

The interferon system was investigated in a long-term culture of guinea pig tongue (GPT) cells. Interferon synthesis was induced with Newcastle disease virus (B strain) and f2 phage double-stranded RNA. Guinea pig interferons were about 2 times more active in cell cultures established from guinea pig embryos than in the GPT cells. Human leukocyte and mouse peritoneal cell interferons were active in this cell system also.

Genomic RNA of the murine coronavirus JHM

Genomic RNA extracted from the purified murine coronavirus JHM sediments between 52S and 54S in aqueous sucrose gradients. The RNA is single-stranded and has an apparent mol. wt. of 5.4 to 6.5 X 10(6), as determined by electrophoresis in polyacrylamide agarose gels of different concentrations. The presence of polyadenylate sequences in the RNA is demonstrated by binding to oligo-)dT) cellulose and digestion with ribonucleases A and T1. The purified RNA does not dissociate into subunits at high temperatures or in high concentrations of DMSO and is infectious.

Reverse transcriptase-associated RNase H activity. II. Inhibition by natural and synthetic RNA

The RNase H activity associated with purified avian myeloblastosis virus and Rauscher murine leukemia virus DNA polymerases is inhibited by homopolymeric RNA molecules, although the efficiency of inhibition by each homopolymer appears enzyme specific. Formation of duplex RNA molecules abolished the inhibitory activity. In contrast to these results, DNA polymerase-independent RNase H activities, such as the RNase H-II from Rauscher murine leukemia virus and calf thymus RNase H, were unaffected by the addition of exogenous RNA molecules to reaction mixtures. These results support the concept (M. J. Modak and S. L. Marcus, J. Virol. 22:253--256, 1977) that the catalytic site of DNA polymerase-associated RNase H activity may be that which is also involved in template binding. Naturally occurring RNA molecules of oncornaviral, procaryotic, or eucaryotic origin also proved to be efficient inhibitors of avian myeloblastosis virus DNA polymerase-associated RNase H activity. In contrast to this result, naturally occurring RNA molecules, at concentrations which inhibited the avian myeloblastosis virus enzyme, did not inhibit Rauscher murine leukemia virus DNA polymerase-catalyzed RNase H activity. This finding represents a new biochemical distinction between the two reverse transcriptases, and may be indicative of differences in the relative affinities of these enzymes for natural RNA molecules.

Inhibition by RNA of RNase H activity associated with reverse transcriptase in Rauscher murine leukemia virus cores

We reported earlier that core preparations of Rauscher murine leukemia virus, when separated on an isopycnic sucrose gradient, did not contain detectable levels of RNase H activity, while retaining high levels of reverse transcriptase activity. We reexamined this phenomenon, and the earlier observation was found to be reproducible. However, when doubly banded preparations of viral cores were solubilized and reverse transcriptase was isolated by ion-exchange chromatography, a coincident peak of a nuclease activity with the specificity of RNase H was observed, which indicated that RNase H was selectively inhibited in the core fractions. By direct activity measurements using the purified reverse transcriptase-RNase H from cores, this endogenous inhibitor has been identified as the viral RNA. Viral 70S RNA strongly inhibited RNase H activity purified either from whole virions or from prefractionated cores. Other RNAs tested that had inhibitory effects were yeast tRNA, polyadenylic acid, and polyguanylic acid. Polyuridylic acid and polyadenylic acid were moderately inhibitory, and polycytidylic acid did not inhibit the RNase H. A rabbit anti-reverse transcriptase immunoglobulin G inhibited both the reverse transcriptase and RNase H activities of the enzyme purified from cores. These data provide a rational explanation for the failure to detect RNase H activity in core preparations of Rauscher murine leukemia virus. Furthermore, these data are consistent with the idea that the RNase H and reverse transcriptase activities purified from cores reside on the same protein molecule. Possible biological implications of the observed inhibition of RNase H by RNA is discussed.

[Interferonogenic and antiviral activity of the double-stranded replicative form of phage f2 RNA in tissue culture and on animals]

Biological activity of a new natural interferon inductor, the replicative RNA form of phage f2 (RFf2) was studied. A possibility of using RFf2 for production of highly active interferon under conditions of superinduction providing an increase in the interferon yield by to 256--512 times as compared to the control samples was shown. The protective interferonogenic and antiviral effect of RFf2 in mice infected with Semliki forest virus (SFV) and tickborne encephalitis virus (TBEV) was studied on administration of the inductor by various routes. It was found that intraperitoneal administration of RFf2 in a dose of 10 gamma per a mouse protected the infected animals from death. It was accompanied by production of up to 1280 units/ml of interferon in the blood serum of the animals. Maximum protection of the animals from death under conditions of the experiment (80 per cent on infection with SFV and 65 per cent on infection with TBEV) was observed when the preparation was administered twice: 4 hours after the infection. Combined use of RFf2 with chemotherapeutics (rimantadine) increased the protective effect both in the tissue culture and in vivo.

Ability of human polymorhonuclear blood cells to produce interferon after induction with phage double-stranded RNA

The ability of human peripheral blood leukocytes to produce interferon in response to phage double-stranded (ds) RNA was studied. Under the conditions used, interferon was produced not only by lymphocytes but also by polymorphs and monocytes. These "pure" cultures showed no marked differences in the degree of interferon production as compared with the mixed leukocyte culture. The involvement of polymorphs in the production of interferon induced by phage ds RNA is discussed.