Translation of RNA from encephalomyocarditis virus in a mammalian cell-free system

Isolation and characterization of alpha-amylase messenger RNA from bank vole parotid glands. Evidence for two separate messenger RNAs coding for amylase and an amylase-related protein

Bank vole saliva contains two glycogen-precipitable proteins, both of which show affinity for the alpha-amylase inhibitor cycloheptaamylose. One of these proteins, amylase, has a molecular weight of 55,000, judged from dodecylsulphate/acrylamide gel electrophoresis. The other has an apparent molecular weight of 59,000 and has no amylase activity. We report here that tryptic peptide maps as well as amino-acid composition analyses indicate extensive homology between the two proteins. We have also isolated total poly(A)-containing mRNA from amylase-rich bank vole parotid glands. These mRNAs were translated in the presence of [35S]methionine in an mRNA-dependent cell-free translation system from rabbit reticulocyte lysate. The radioactive translation products were examined by dodecylsulphate/polyacrylamide gel electrophoresis. Two major translation products with apparent molecular weights of approximately 56,500 and 60,500, respectively, were further characterized by tryptic peptide analyses. Our data indicate that the 56,500-Mr product is the biosynthetic precursor of amylase, whereas the 60,500-Mr translation product is a precursor of the 59,000-Mr amylase-like protein. Both precursors appear to contain extra peptide material, presumably as amino-terminal 'pre' or 'signal' peptides, in analogy with that found for other precursors of secretory proteins. Thus, amylase and the 59,000-Mr protein, although very similar, are translated from two separate mRNAs. These two messengers sediment in a sucrose gradient at about 17-S, corresponding to lengths of about 1,800 nucleotides.

Translation of encephalomyocarditis virus RNA in vitro yields an active proteolytic processing enzyme

In contrast to other cell-free translation systems, the mRNA-dependent reticulocyte lysate can translate encephalomyocarditis virus RNA efficiently and completely when supplemented with heterologous tRNA. Cleavage of the nascent polypeptide chain occurs, and one of the translation products appears to be a specific proteolytic enzyme which correctly processes the primary products. The identity of the proteins made in vitro was verified by comparison with infected cell proteins on dodecylsulphate/polyacrylamide gels, and by mapping their coding sequences on the viral genome.

The purification and properties of two low-molecular-weight proteins required for the initiation of translation in ascites tumour cells

A fractionated cell-free protein-synthesising system from Krebs II ascites tumour cells is described. It is dependent on the addition of exogenous mRNA. In this system the translation of natural mRNAs requires the presence of four initiation factors: the high-molecular-weight complex IF-M3, IFEMC and two low-molecular-weight proteins IF-Malpha and IF-Mbeta. None of these factors are required for the translation of the synthetic messenger poly(A,U,G). The purification of IF-Malpha and IF-Mbeta was achieved by the use of gel and ion-exchange chromatography. Analysis of the purified proteins by sodium dodecyl sulphate/polyacrylamide gel electrophoresis showed that the molecular weight of IF-Malpha is 19,000 and that of IF-Mbeta is 15,000. The initiation factor IF-E1 isolated from rabbit reticulocytes can substitute for IF-Mbeta in the translation of encephalomyocarditis virus RNA. IF-Malpha does not correspond to any previously recognised eukaryotic initiation factor.

Procollagen biosynthesis by embryonic-chick-bone polysomes. Estimation of the relative numbers of active proalpha1 and proalpha2 messenger ribonucleic acids

Both total polysomes and polysomes of different size classes isolated from embryonic chick cranial bones were allowed to complete their nascent polypeptide chains in a cell-free system containing rabbit reticulocyte post-ribosomal supernatant fraction. In this system, no de novo initiation of polypeptide synthesis occurred. The product was analysed for relative content of proalpha1 and proalpha2, the precursors of the alpha chains of collagen, by dodecylsulphate-acrylamide gel electrophoresis as well as by paper electrophoresis following tryptic digestion. The results showed that the products of polysome protein synthesis contained proalpha1 and proalpha2 in the 2:1 ratio in which the corresponding alpha chains are present in native collagen, and that proalpha1 and proalpha2 synthesising polysomes are of the same size. These findings, in conjunction with results from a previous report (Vuust, J. and Piez, K.A. (1972) J. Biol. Chem. 247, 856-862) suggest that active messenger ribonucleic acids for the proalpha1 and proalpha2 chains, respectively, are present in the cells in a ratio of 2:1, and that the rates of initiation, elongation, termination and release from polysomes are all identical for the two chains.

A transfer RNA-dependent protein synthesizing system from Ehrlich ascites extracts

An homologous cell-free system from Ehrlich ascites cells was made tRNA dependent by passing both the ribosomes and the ammonium sulfate fraction through DEAE-cellulose columns in 0.30 M KCl. Protein synthesis was routinely stimulated 20-50 fold by the addition of 100 mug/ml of ascites cell tRNA in the presence of oviduct mRNA, ascites mRNA, or encephalomyocarditis RNA.

Cell-free synthesis of rat growth hormone

Growth hormone has been synthesized in a cell-free system derived from Krebs II ascites cells, under the direction of RNA prepared from rat pituitary tumor (GC) cells. Growth hormone synthesized in the cell-free system was identified by precipitation with antiserum against growth hormone developed in baboon, followed by electrophoretic analysis of the dissolved precipitate on sodium dodecyl sulfate-polyacrylamide gels. RNA from both the membrane and the post-membrane fractions of the cytoplasm of GC cells stimulated protein synthesis in the cell-free system, but only RNA from the membrane fraction was found to direct the synthesis of growth hormone.

In vitro translation of oogenetic messenger RNA of sea urchin eggs and picornavirus RNA with a cell-free system from sarcoma 180

A cell-free protein-synthesizing system prepared from mouse sarcoma 180 was characterized by use of RNA from mengo virus and sea urchin egg. In the presence of exogenous mammalian transfer RNA, total sea urchin egg RNA and mengo RNA direct incorporation of [(3)H]leucine into acid-insoluble material. The system is extremely efficient in that a stimulation of 100-times over background can be obtained. Studies with formylmethionyl-transfer RNA, as well as with inhibitors of initiation, indicate that multiple initiation occurs; further, 85-90% of all chains made in vitro are subsequently released from ribosomes. An average translation time of 3.5 min was determined with messenger RNA of sea urchin egg, and product analysis indicates that high-molecular-weight products (greater than 50,000 molecular weight) are being made in vitro. Sequences of sea urchin egg RNA containing poly(A) act as messenger RNA.

Methionine transfer ribonucleic acids of avian myeloblastosis virus

Chick-embryo cells contain four isoaccepting species of methionine transfer RNA (I-IV). One species (I) is the initiator, tRNA(f) (Met), and the others (II, III, and IV) are the donors of internal methionyl residues (tRNA(m) (Met)). Over 85% of the tRNA(Met) in purified avian myeloblastosis virus consists of one tRNA(m) (Met) species, which resembles host-cell tRNA(Met) IV with respect to chromatographic properties on RPC-5, electrophoretic mobility of the terminal methionyl-oligonucleotide, and activity in cell-free protein synthesis in response to synthetic and natural messenger RNAs. Thus, tRNA(Met) IV of avian myeloblastosis virus is structurally indistinguishable from the corresponding host-cell species, and, although not involved in initiation of viral protein synthesis, is able to function in peptide-chain elongation.

Cell-free translation of maternal messenger RNA from sea urchin eggs

The template activity of RNA extracted from unfertilized sea urchin eggs was demonstrated in a cell-free translation system, and, for the first time, specific proteins were identified among the products. All messenger RNA activity is recovered, under the conditions used, from the postribosomal supernatant. Histones, among many other proteins, were identified specifically as products of this "maternal" messenger RNA.

Translation of encephalomyocarditis viral RNA in oocytes of Xenopus laevis

RNA from encephalomyocarditis virus was injected into oocytes of Xenopus laevis. After incubation of the oocytes in [(35)S]methionine, polyacrylamide gel electrophoresis showed that a new series of polypeptides had been synthesized. They were identical in size to the polypeptides that appeared in ascites cells after infection with this virus. Electrophoretic and chromatographic analysis of the methionine-containing tryptic peptides from three of the induced polypeptides confirmed that they were virus-specific. All of the bands that appeared in ascites cells after infection also appeared in oocytes after injection of RNA from the virus. We conclude that Xenopus oocytes translate a mammalian viral mRNA faithfully and extensively, and perform normal post-translational modifications.

Translation of reovirus messenger RNAs synthetesized in vitro into reovirus polypeptides by several mammalian cell-free extracts

Single-stranded reovirus RNA, synthesized in vitro by reovirus cores, functioned as messenger RNA in cell-free extracts prepared from several mammalian cells: Krebs II mouse ascites cells, mouse L cells, Chinese hamster ovary cells, HeLa cells, and rabbit reticulocytes. As shown by acrylamide gel electrophoresis, all eight polypeptides known to be specified by reovirus were synthesized in the reticulocyte system. In the other extracts, from 5 to 7 complete virus proteins were made.

Characterization of the polypeptides formed in response to encephalomyocarditis virus ribonucleic acid in a cell-free system from mouse ascites tumor cells

The polypeptide products synthesized at different times in a cell-free system from Krebs mouse ascites tumor cells in response to the addition of encephalomyocarditis (EMC) virus ribonucleic acid (RNA) were characterized by electrophoresis on polyacrylamide gels and fingerprint analysis of their tryptic peptides. Translation of the EMC RNA genome with time occurred in a nonrandom fashion in these systems, to yield products containing sequences characteristic of both virion capsid polypeptides and EMC-specific polypeptides present only in the infected cell. The molecular weights of the products fell in a series from 20,000 to 140,000 daltons, although occasionally traces of larger polypeptides were also observed. All of the major polypeptides appeared to arise from partial or complete translation of about 60% of the EMC RNA genome. They were not formed by cleavage of a large precursor molecule. It is suggested that they are artifacts generated by premature "termination" of nascent polypeptide chains at preferred sites.

Purification of biologically active globin messenger RNA by chromatography on oligothymidylic acid-cellulose

A convenient technique for the partial purification of large quantities of functional, poly(adenylic acid)-rich mRNA is described. The method depends upon annealing poly(adenylic acid)-rich mRNA to oligothymidylic acid-cellulose columns and its elution with buffers of low ionic strength. Biologically active rabbit globin mRNA has been purified by this procedure and assayed for its ability to direct the synthesis of rabbit globin in a cell-free extract of ascites tumor. Inasmuch as various mammalian mRNAs appear to be rich in poly(adenylic acid) and can likely be translated in the ascites cell-free extract, this approach should prove generally useful as an initial step in the isolation of specific mRNAs.

Simple method for the isolation of encephalomyocarditis virus ribonucleic acid

A simple purification procedure for encephalomyocarditis virus is described, yielding material suitable for extraction of viral ribonucleic acid for use as messenger in animal cell-free systems.

Synthesis of and chains of rabbit hemoglobin in a cell-free extract from Krebs II ascites cells

An RNA sedimenting at 10 S, with a molecular weight of 2.3 x 10(5), was isolated from rabbit reticylocyte polyribosomes. When this RNA is added to a cell-free extract from Krebs II ascites cells, both alpha and beta chains of rabbit hemoglobin are synthesized; beta chains are made in about 50% excess over alpha chains.

Synthesis of capsid and noncapsid viral proteins in response to encephalomyocarditis virus ribonucleic acid in animal cell-free systems

The polypeptide products formed in two cell-free protein-synthetic systems programmed with encephalomyocarditis (EMC) virus ribonucleic acid (RNA) have been compared with the virus-specific proteins found in EMC-infected cells and with the capsid proteins of the purified virion. Tryptic peptides of (35)S-methioninelabeled proteins from these three sources were compared by co-chromatography and electrophoresis and by isoelectric focussing. Fifty-two methionine-containing peptides were resolved in digests of material from infected cells, of which about one-third were also clearly present in digests of the virion capsid proteins. The product formed in response to EMC RNA in cell-free systems from Krebs mouse ascites tumor cells yielded 26 to 29 such peptides. Most of these peptides were shown to behave identically with virus-specific peptides from infected cells, whereas just under half of them appeared to be identical with peptides from the virion capsid proteins. The product formed in response to EMC RNA in the L-cell cell-free system was similar, whereas six additional EMC-specific peptides were detected in mixed Krebs L-cell systems. The results indicate that the EMC RNA genome is partially translated in the mouse cell-free systems used to yield products containing both virion capsid and virus-specific noncapsid polypeptides.

Protein synthesis directed by encephalomyocarditis virus RNA: properties of a transfer RNA-dependent system

Small amounts of encephalomyocarditis virus RNA direct a 50-fold increase in amino acid incorporation, in appropriately supplemented ascites tumor cell extracts, under conditions that give rise to authentic viral polypeptides. Incorporation in these crude extracts has a novel characteristic, namely, that it is almost entirely dependent upon the addition of exogenous tRNA. Further, this incorporation is restricted in that tRNA derived from ascites tumor cells or from rat liver permits translation of viral RNA, whereas tRNA from yeast or Escherichia coli does not. These translational barriers are due, at least in part, to an incompatibility between the tRNA of yeast and E. coli and the aminoacyl-tRNA synthetases of the ascites tumor cell. A more extensive basis for this incompatibility is suggested, however, by the failure of the E. coli aminoacyl-tRNA synthetases to restore viral RNA-directed protein synthesis in the presence of tRNA from E. coli, although the coli synthetases fully restore the poly(U)-directed synthesis of polyphenyl-alanine. The possible role that unique or favored codon classes might play in this restriction is considered, together with the implications of the observed requirement for tRNA.

Virus protein synthesis in animal cell-free systems: nature of the products synthesized in resonse to ribonucleic acid of encephalomyocarditis virus

Ribonucleic acid (RNA) from encephalomyocarditis (EMC) virus stimulates the incorporation of amino acids into protein in cell-free protein-synthetic systems derived from Krebs mouse ascites tumor cells and chick embryo fibroblasts; the mouse system is the more responsive to the viral RNA. The greater part of this difference in activity can be ascribed to the cell sap, but the origin of the ribosomes also has a marked effect. The nature of the polypeptides formed in these cell-free systems was investigated by electrophoresis on polyacrylamide gels and by fingerprint analysis of tryptic digests. The same product in part appears to be synthesized in response to the EMC RNA in both systems. It was not detected if the EMC RNA was partly degraded (</=4S) or replaced by other species of RNA, including that from influenza virus. The results suggest that EMC RNA is partially translated in these systems to yield virus-specific polypeptides.

Protein synthesis in cell-free systems: an effect of interferon

The activity of ribosome and cell-sap fractions from interferon-treated and control chick embryo fibroblasts was compared in mixed chick-mouse and purely chick cell-free systems capable of the synthesis of viral polypeptide(s) in response to viral ribonucleic acid (RNA). Interferon treatment of cells did not affect the intrinsic amino acid incorporation activity of these systems or their response to polyuridylic acid. With encephalomyocarditis (EMC) virus RNA as messenger, however, a fraction of the ribosomes from interferon-treated cells appeared less active than parallel controls. The results obtained with the corresponding cell-sap fractions were variable. Although competition between endogenous and added messengers cannot be excluded in these systems, a reduced level of translation of EMC RNA with interferon-treated cell ribosomes was also suggested by the results of analyses of tryptic digests of the products formed in response to the RNA. In addition, these analyses showed that this reduced activity must reflect a reduction in the rate or frequency of translation rather than a decrease in the length of the EMC RNA translated, for the same polypeptides were synthesized in response to the RNA with material from interferon-treated and control cells. Interferon added directly to the cell-free system was without effect. Although suggestive, these results do not provide definitive evidence for or against the hypothesis that virus protein synthesis is inhibited at the translational level in the interferon-treated cell. Possible alternative interpretations of the data are discussed.