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At least 19 recordsLinked to original sources
PubMed1978

Translation of ascites and mengovirus RNA in fractionated cell-free systems from uninfected and mengovirus-infected Ehrlich-ascites-tumor cells.

We have prepared homologous, fractionated, cell-free translational systems from uninfected and mengovirus-infected Ehrlich ascites tumor cells in order to determine what alterations occur following virus infection in the translational machinery of the host cell. Two major differences distinguish the system developed from infected cells. First, it has a 40% lower rate of protein synthesis, primarily a consequence of the rate of chain elongation, which is depressed to 60 amino acids/min from 90 amino acids/min in the system from uninfected cells. Second, at supraoptimal concentrations of Mg2+ and K+ the system from virus-infected cells supports the translation of mengovirus RNA but not host mRNA. These differences between the two systems may reflect specific changes which are responsible for the selective translation of mengovirus RNA in the infected cell. In both systems the optimal concentrations of polyamines, monovalent and divalent cations, mRNA, and ribosomal subunits are the same for the translation of either host or viral RNA. This uniformity is useful in experiments, designed to investigate the selective translation of viral RNA, where various components of the two systems are interchanged.

Animals↗
PubMed1978

Selective translation of mengovirus RNA over Host mRNA in homologous, fractionated, cell-free translational systems from Ehrlich-ascites-tumor cells.

The selective translation of viral RNA in mengovirus-infected Ehrlich ascites tumor cells was investigated using fractionated translational systems whose macromolecular components were derived entirely from uninfected or virus-infected cells. Both systems translate host mRNA from uninfected cells, host mRNA from virus-infected cells, and mengovirus RNA. In competition experiments, where viral RNA and host mRNA were translated together in systems from uninfected cells, the relative amounts of virus-specific and host-specific proteins synthesized were proportional to the relative concentrations of the RNA templates. In systems whose components were obtained from virus-infected cells, mengovirus RNA was preferentially translated. 70% of the selectivity found in the translational systems derived from infected cells was due to the initiation factor fraction, the remaining 30% to components of the pH 5 enzyme fraction. In addition, host mRNA isolated after virus infection is translated in vitro to a lower extent in the presence of mengovirus RNA than is host mRNA from uninfected cells.

Animals↗
PubMed1976

Protein synthesis in postnuclear supernatants from mengovirus-infected Ehrlich ascites tumor cells.

The effect of mengovirus infection on the protein synthetic capacity of Ehrlich ascites tumor cells cultured in vitro was studied in vivo and in vitro employing postnuclear supernatants prepared at various times post-infection in the absence and in the presence of 1% Triton X-100. The amino acid incorporating activities of extracts obtained in the presence of the detergent were reduced by about 30% compared with the capacities of the corresponding postnuclear supernatants prepared in the absence of Triton X-100; but the course of the activity vs. time curve was not influenced by the detergent. Under the conditions employed, the postnuclear supernatants were unable to reinitiate protein synthesis once elongation of nascent polypeptide chains concomitant with ribosome runoff was completed. After mengovirus infection, a gradual disappearance of polysomes from postnuclear supernatants and a simultaneous accumulation of monosomes was observed. The protein-synthesizing activities of normal and infected cells were inversely proportional to the monosome concentrations of their corresponding extracts. Qualitatively, protein synthesis in intact cells and in postnuclear supernatants responded similarly to mengovirus infection. In both cases an initial reduction of host-specific amino acid incorporation was followed by a burst of viral protein synthesis. However, the two activity vs. time curves showed the following significant differences: 1) The activities of extracts from control cells and from mengovirus-infected cells nearly in the infectious cycle were low compared with the activities observed in vivo. 2) In the middle of the infectious cycle, the peak of viral protein synthesis occurred later and the activity was higher in vitro. 3) Finally, in the late period of the infectious cycle the postnuclear supernatants had considerable protein synthesizing activity, at a time when protein synthesis in vivo was nil.

Animals↗
PubMed1977

An investigation of the stability of messenger RNAs in cell-free, translational systems from uninfected and mengovirus-infected Ehrlich ascites tumor cells.

The stabilities and translation of Ehrlich ascites tumor cell poly(A)-containing mRNA and mengovirus RNA in fractionated cell-free protein synthesizing systems from uninfected and mengovirus-infected Ehrlich ascites tumor cells were studied. During incubation of the systems about 20% of the input RNA is reduced in size and associated with ribosomes engaged in polypeptide synthesis; the remainder is rapidly degraded by RNases. At the end of active translation, both mRNA and nascent proteins are bound to polysomes which are of the same size as those formed during active protein synthesis. The kinetics of protein synthesis closely follow those of RNA hydrolysis. The stabilities of mengovirus RNA and poly(A)-containing mRNA from Ehrlich ascites tumor cells are the same in both systems.

Animals↗
PubMed1978

Purification of mengovirus by freon extraction and chromatography on protein-coated controlled pore glass.

Mengovirus, extracted from infected L-cell cultures with Freon 113 and concentrated from the aqueous phase with polyethyleneglycol, was chromatographed on protein-coated controlled pore glass (CPG). The covalent binding of protein to CPG is described. Further purification and concentration of mengovirus was achieved by isopycnic density gradient centrifugation in solutions of either CsCl or salts of iodinated benzoic acid derivatives. The described procedure is superior to conventional methods for the isolation and purification of large quantities of mengovirus. It yields highly purified virus preparations within a short time and a recovery of more than 50% of the starting infectivity.

Chemical Precipitation↗
PubMed1977

Effects of pyrimidine derivatives on RNA-dependent RNA polymerase of mengovirus-infected Fogh and Lund (FL) cells.

Two newly synthesized pyrimidine derivatives were found to possess antiviral activity against Mengovirus in Fogh and Lund (FL) cells and in a cell-free system. The inhibitory effect on RNA-dependent RNA polymerase of Mengovirus-infected FL cells was assayed using 14C-UTP as precursor. Addition of 50 or 100 muM of the inhibitors in a cell-free system of crude enzyme and nucleoside triphosphate medium for 60 min incubation at 37 degrees C resulted in about 40 to 60% lower counting rates for drug-treated reaction mixtures. The analysis of the polymerase synthesis product (virus RNA extracted from the cell-free reaction mixture and deproteinized by the phenol-SDS method) was carried out by means of agarose-acrylamide gel electrophoresis. The main finding was a reduction of single-stranded Mengovirus RNA (RNase-sensitive and LiCl-precipitable). The rates of synthesis of the replicative intermediate (LiCl-precipitable) and the replicative form of RNA (LiCl-soluble) were not significantly influenced.

Antiviral Agents↗
PubMed1977

Fate of histone messenger RNA in mengovirus-infected Ehrlich ascites tumor cells.

Histone mRNA was isolated from mengovirus-infected Ehrlich ascites tumor cells at various times postinfection and quantitated in a reticulocyte cell-free protein-synthesizing system. The amount of translatable histone mRNA decreases during the first hour postinfection by 30%, rises during the following 1-1.5 h by 10-15%, drops progressively in the further course of infection, and reaches 20% of the control at the end of the infectious cycle (8-9 h postinfection). On the basis of the relative histone mRNA contents, the histone-synthesizing potentials of mengovirus-infected Ehrlich ascites tumor cells are substantially higher throughout infection than actually expressed in vivo. This result indicates that the virus-induced shutoff of histone synthesis is not directly the consequence of inactivation or degradation of histone mRNA. Most of the histone mRNA recovered from mengovirus-infected Ehrlich ascites tumor cells is bound to ribosomes. Late in infection, certain mRNAs are co-isolated with histone mRNAs, very likely due to loss or shortening of poly(A) occurring after release of the mRNAs from polyribosomes.

Animals↗
PubMed1975

Host-dependent restriction of mengovirus replication. II. Effect of host restriction on late viral RNA synthesis and viral maturation.

Restricted mengovirus replication in Mandin-Darby bovine kidney (MDBK) cells is characterized by a 400-fold reduction in infectious virus yield and a 40-fold increase in the production of noninfectious virus. Using conditions which insure that all MDBK cells are infected, virus-specific RNA and protein synthesis were measured in the restrictive host and in a permissive host for mengovirus, HeLa cells. Labeling kinetics and sucrose gradient analysis of mengovirus-specific RNA from MDBK cells show a reduction of 10-fold in virion RNA, 5-fold in double-stranded RNA, and 12.5-fold in single-stranded RNA. The viral RNA biosynthetic processes which occur late in the replicative cycle and result in the production of 90% of the single-stranded viral RNA that is packaged into capsid proteins in the permissive host are absent in restrictive MDBK cells. Viral protein synthesis as measured by labeled viral-specific polysome is decreased, and there is an accumulation of 80S subviral particles in the restricted host. It is suggested that restriction may act at a number of stages of viral replication and maturation.

Amino Acids↗
PubMed1976

Cellular protein synthesis shutoff by mengovirus: translation of nonviral and viral mRNA's in extracts from uninfected and infected Ehrlich ascites tumor cells.

The mechanism whereby picornaviruses inhibit host protein synthesis while their own synthetic processes proceed unabated has remained elusive. One of our approaches to this problem was to study the ability of cell-free extracts derived from uninfected and mengovirus-infected Ehrlich ascites tumor cells to translate viral and nonviral mRNA's under various conditions of incubation. Our results indicate that viral messengers (from mengovirus and encephalomyocarditis virus) and cellular messengers [L cell and Ehrlich ascites tumor poly(A)-containing mRNA's, rabbit globin mRNA, and chicken embryo lens crystallin mRNA] are translated equally well in both extracts. We also examined the simultaneous translation of viral and nonviral mRNA's in extracts from uninfected Ehrlich ascites tumor cells. Our results indicate that under certain conditions mengovirus RNA can suppress completely the translation of globin mRNA. The significance of these results in terms of the shutoff of host protein synthesis is discussed.

Animals↗
PubMed1977

Factors affecting composition and thermostability of mengovirus virions.

The composition of mengovirus virions produced by infected cells varies with the incubation temperature. Virons produced at 37.0 or 39.5 degrees contain four major polypeptides (alpha, beta, gamma, and delta) and one minor polypeptide (beta'). Virons produced at 31.5 degrees C contain two additional polypeptides (D1 and E). The virions of two temperature-sensitive (ts) and thermolabile mutants of mengovirus (ts25 and ts88) contain an increased amount of polypeptide beta', with a corresponding decrease in polypeptide beta when compared with the wild-type mengovirus.

Mengovirus↗
PubMed1978

Enhanced phosphorylation of ribosomal protein s6 and other cytoplasmic proteins after mengovirus infection of Ehrlich ascites tumor cells.

After mengovirus infection of Ehrlich ascites tumor cells, an increased incorporation of radioactive phosphate into ribosomal protein S6 was detected. As judged from the shape of the radioautography spot and the location of the modified protein on the two-dimensional polyacrylamide gel, it must be concluded that more than one phosphate group was incorporated into ribosomal protein S6. Concomitantly, multiple cytoplasmic proteins, particularly those with high affinity for ribosomes, were phosphorylated. Compared with the controls (mock infection), mengovirus infection induced only a slight additional phosphorylation of the proteins of the ribosome-free supernatant. Employing the radio isotope dilution test with 3', 5'-cyclic AMP-binding protein, no enhancement of the intracellular concentration of 3', 5'-cyclic AMP in response to mengovirus infection could be deomonstrated.

Animals↗
PubMed1977

Shutoff of histone synthesis by Mengovirus infection of Ehrlich ascites tumor cells.

The histone synthesizing capacity of mengovirus-infected Ehrlich ascites tumor cells and of their corresponding postnuclear supernatants was investigated as a funcion of time post-infection. In addition, histone synthesis was compared with the synthesis of other basic host proteins under identical conditions. In the scope of mengovirus infection of Ehrlich ascites tumor cells the less complex fraction comprising basic protein, separated from the acidic proteins by carboxymethyl cellulose chromatography, can be regarded as a representative of total host protein. Histones and the remaining basic host proteins therefore are well suited as easily identifiable indicators of the host protein synthesizing potential of mengovirus-infected Ehrlich ascites tumor cells. The cessation of histone synthesis proceeds faster than the arrest of the synthesis of other basic host protein.

Animals↗
PubMed1977

Coding capacity of poly(A)+mRNA isolated from mengovirus-infected Ehrlich ascites tumor cells.

Total poly (A)+mRNA was isolated from mengovirus-infected Ehrlich ascites tumor cells at various times postinfection and quantitated in a cell-free system derived from uninfected ascites cells. Basic proteins were separated from acidic proteins by carboxymethyl cellulose chromatography. At the end of the infectious cycle, 8h postinfection, the cellular contents of most mRNAs coding for basic ribosomal proteins are still between 70 and 90 percent of those measured at the beginning of infection or in uninfected cells. On the basis of this result, the rapid shutoff of host protein synthesis after mengovirus infection of Ehrlich ascites tumor cells cannot be the consequence of the inactivation of host template RNA.

Animals↗
PubMed1978

Localization of host poly(A)+ mRNA in the ribosome profile of mengovirus-infected Ehrlich ascites tumor cells.

The distribution of poly(A)+ mRNA among polysomes, monosomes, and ribosome-free supernatant fractions after mengovirus infection of Ehrlich ascites tumor (EAT) cells was investigated employing sucrose gradient centrifugation of their corresponding postnuclear supernatants. Poly(A)+ mRNA was isolated from sucrose gradient fractions and quantitated in a cell-free protein synthesizing system from uninfected EAT cells. It was also localized by annealing [3H]-poly(U) to the poly(A)-tracts of mRNA present in the sucrose gradient fractions. Both experiments revealed a gradual shift of host poly(A)+ mRNA from large to small polysomes and monosomes, respectively, with the time postinfection. The greatest part of host template RNA appears to remain ribosome-bound and only a fraction seems to be detached from the ribosomes in the course of mengovirus infection. At the end of the infectious cycle, 8 h postinfection, approximately 70% of the poly(A)+ mRNA detected in uninfected cells is still biologically active, but not translated in vivo, in agreement with data from the [3H]poly(U)hybridization experiment.

Animals↗
PubMed1978

Dephosphorylation of histone H1 after mengovirus infection of Ehrlich ascites tumor cells.

The effect of mengovirus infection on the extent of phosphorylation of histone H1 was studied in Ehrlich ascites tumor cells. After prelabeling of the nuclear protein with [32P] orthophosphate, the excorporation of radioactivity was followed as a function of time postinfection. Employing high-resolution polyacrylamide gradient slab gel electrophoresis and autoradiography, it was found that, compared to a relatively slow turnover of phosphate groups in histone H1 in mock-infected cells, in mengovirus-infected cells the excorporation of radiolabel from histone H1 was significantly enhanced. In the latter case, the decrease of histone-bound radioactivity was paralleled by a reduction of the band multiplicity in the histone H1 region of the electrophoresis profile. It was also shown that the microheterogeneity in the histone H1 complements isolated at various times postinfection was reduced to the same basal 3-band level by incubation of the nuclear protein fractions in the presence of alkaline phosphatase. After this treatment, the band multiplicity equaled that found in histone H1 from stationary cells.

Animals↗
PubMed1976

Considerations on structure-activity relationships with mengovirus of substituted 5-amino-4-cyanopyrazoles.

In a screening program using the agar diffusion-plaque inhibition test, 22 out of 27 substituted aminopyrazoles tested showed marked antiviral activity against mengovirus in FL cell cultures. The efficacy of the different derivatives was compared by determining their effect on the yield of infectious virus after a one-step growth cycle. The antiviral activity against mengovirus correlated with the chain length of the substituents and increased or decreased according to the position of the side chain.

Antiviral Agents↗
PubMed1975

Physiological characterization of temperature-sensitive mutants of mengovirus.

Twenty-four temperature-sensitive mutants of mengovirus were characterized physiologically with respect to phenotype. The mutants were separated into four classes on the basis of viral RNA synthesis. L-67-S cells infected with five of the mutants synthesized little viral RNA at 39.5 C. These mutants are designated RNA-. One mutant is designated RNA* since its RNA synthesis is altered at both 39.5 and 31.5 C. The other mutants were divided into two groups, RNA plus or minus (25 TO 49% of wild-type RNA synthesis) and RNA plus (50 to 100% of wild-type RNA synthesis). The time of expression of the mutation in the RNA- mutants was estimated from the results of reciprocal temperature-shift experiments. The mutatation in ts12 appears to be expressed at the time RNA synthesis normally begins. The defect in three of the mutants was expressed 1 to 2 h before RNA synthesis is normally detectable. Protein synthesis is required before RNA synthesis begins when the cells are shifted from 39.5 to 31.5 C. The RNA polymerase synthesized by cells infected with these RNA- mutants at 31.5 C was stable and fully active when assayed at 39.5 C in vitro. The sedimentation profiles of the viral RNA synthesized by cells infected with RNA plus and RNA plus or minus mutants are similar to wild-type profiles with the exception of ts148. Cells infected with this RNA plus or minus mutant synthesize RNA that sediments in a sucrose gradient like replicative-intermediate RNA, but little mature viral RNA is evident. The results of step-up experiments indicate that the temperature-sensitive period for the majority of the RNA plus and RNA plus and minus mutants extends through most of the replicative cycle. The temperature-sensitive defect of four of the mutants, however, was expressed in the first hour, suggesting that some undefined early function is required for the eventual maturation of mengovirus. The virions of three of the RNA- mutants were more thermolabile than wild-type virions. Five of the RNA plus and RNA plus or minus mutants were also thermolabile. Genetic complementation at a significant level was not detectable in mixed infections of the mutants described.

Animals↗