Protein Synthesis Directed by an Arbovirus

In contrast to chick embryo fibroblast protein synthesis, the bulk of the protein synthesis directed by Semliki Forest virus is carried out on membranes. Under conditions where more than 95% of cell protein synthesis was inhibited, viral polysomes could be demonstrated. Viral protein appeared to be produced on polysomes associated with nascent ribonucleic acid strands still attached to the base-paired, double-stranded replicative form of the virus. Very rapid incorporation of virus protein into 140S virus core particles was also demonstrated.     

Inhibition of Protein Synthesis by RA-VII

The antitumor natural product RA-VII has been evaluated as an inhibitor of protein synthesis in vitro. Complete inhibition of protein synthesis in rabbit reticulocyte lysates is observed with 5 μM RA-VII. Mechanistic studies using purified elongation factors and ribosomes identify RA-VII as a peptidyltransferase inhibitor. Thus, similar to the related natural products bouvardin and RA-XII, RA-VII appears to function by binding to eukaryotic ribosomes.     

Inhibition by Thiopeptin of Bacterial Protein Synthesis

Thiopeptin, a sulfur-containing antibiotic, was found to inhibit protein synthesis in a bacterial ribosomal system. The pretreatment of ribosomal subunits with the antibiotic revealed that thiopeptin may act on the 50 S ribosomal subunit. The elongation of peptide chain on the ribosome is more profoundly blocked by the antibiotic than the initiation of protein synthesis. It was demonstrated that thiopeptin inhibits elongation factor (EF)-Tu-dependent GTP hydrolysis and binding of aminoacyl-tRNA to the ribosome. The peptidyl transferase-catalyzed puromycin reaction is not significantly affected by the antibiotic. Thiopeptin inhibits EF-G-associated GTPase reaction, and translocation of peptidyl-tRNA and mRNA from the acceptor site to the donor site. Protein synthesis in ribosomal systems, obtained from rat liver and rabbit reticulocytes are insensitive to the antibiotic.     

Inhibition of Cell-Free Protein Synthesis by Hydrostatic Pressure

Pressure inhibition of cell-free polypeptide synthesis is manifested in the same manner as that observed in the intact cell: (i) starting at approximately 200 atm, there is a progressive inhibition with increasing pressures; (ii) there is complete inhibition at 680 atm; (iii) incorporation into polypeptide is instantaneously reversible after pressure release and proceeds at a rate parallel to an atmospheric control; and (iv) the volume change of activation (DeltaV*) is 100 cm(3)/mole. Peptide bond formation per se can occur at a pressure level which is totally inhibitory to polypeptide synthesis. The one investigated step in translation that is inhibited in an identical manner is the binding of aminoacyl-transfer ribonucleic acid (AA-tRNA) to the ribosome-messenger RNA (mRNA) complex. The volume change of activation (DeltaV*) calculated for the binding reaction is also 100 cm(3)/mole. Thus, the inability of AA-tRNA to bind to ribosomes and mRNA under pressure, possibly in conjunction with translocation, appears to be responsible for the observed inhibition of the translational mechanism.     

Inhibition of Protein Synthesis by Antiviral Protein from Yucca recurvifolia Leaves

We analyzed 18S and 26S rRNA partial base sequences [positions 1451–1618 (168 bases) of 18S rRNA and positions 1611–1835 (225 bases) and 493–622 (130 bases) of 26S rRNA] of a total of three strains of Pichia jadinii and Candida utilis. The three strains had identical base sequences with the type strain of P. jadinii (IFO 0987) in the 18S rRNA partial base sequencings. In the 26S rRNA partial base sequencings, there were partial base sequences similar to each other (1–0 base difference and 87–95 percent similarities). The sequence data obtained are discussed taxonomically and phylogenetically, especially in connection with Williopsis saturnus, the type species of the genus Williopsis ZENDER.     

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.     

Inhibition of Plant Viruses by Human Gamma Interferon

In order to evaluate the inhibitory effect induced by gamma interferon (Hu g IFN) on plant viruses, pre-inoculation treatments (brushing the leaves) were carried out in two different plant-virus systems: D. stramonium* TMV and G. globosa* PVX. Results showed that Hu g IFN induced a higher inhibitory effect (IP = 90%) in D. stramonium* TMV system (Table 1). Comparing the antiviral effect of the three IFNs: gamma, alpha and beta-like interferons, it was verified that Hu g IFN was more effective than the other two (Table 2). Hu g IFN was also used for post-inoculation treatments (incubation of tobacco leaf-discs) and using different dilutions a dose response curve could be obtained (Fig. 1). Hu g IFN inhibitory effect was confirmed by the neutralization of its inhibitory effect using monoclonal antibody (Table 3). Results suggest that although the three IFNs differ in their composition, they present similarities in their biological activities probably triggering an antiviral state in plants.     

Membrane Binding of Input Arbovirus Ribonucleic Acid: Effect of Interferon or Cycloheximide

By 1 hr after infection, 36% of input Semliki Forest virus ribonucleic acid (RNA) which was cell associated was found in a membrane structure. This structure had many similarities to the membrane-associated replication complex (MRC) which had previously been identified in arbovirus infections. Interferon treatment did not affect the association of viral RNA with the MRC structure, but cycloheximide treatment inhibited it.     

Induction of Colicin Production by High Temperature or Inhibition of Protein Synthesis

Escherichia coli K-12 colicinogenic for ColE1 yielded mutants that appeared to produce colicin at 43 C but not at 30 or 37. These mutants proved to have the mutation recA⁻ Further study revealed that both recA⁻ and recA⁺ bacteria, when carrying ColE1 or ColE2, produce more colicin during growth at higher temperatures or after brief exposure to temperatures beyond the growth range. Counts of lacunae demonstrated that the increase of colicin production is due to an increase in the number of cells that yield colicin. Heat treatment causes lacunae to increase by the same factor in recA⁺ and recA⁻ cells, although recA⁻ bacteria produce 500 times fewer lacunae than recA⁺. Inhibition of protein synthesis, notably by chloramphenicol, also induces colicin production in as much as 90% of the cells after removal of inhibition (to permit colicin synthesis). Induction of colicin production by chloramphenicol requires that ribonucleic acid synthesis continue during the period of inhibition. These results are discussed in relation to the regulation of colicin production.     

Inhibition of Macrophage Migration by Virus-Induced Interferon Preparations1

It was found that a preparation of mouse L cell interferon induced by Newcastle disease virus (NDV) possessed not only interferon activity but also inhibitory activity upon migration of guinea pig peritoneal macrophages (MIF activity). These activities were also observed in a preparation of human leukocyte interferon induced by NDV. The interferon and MIF activities shared common characteristics in the dose response, time course of in vitro production, thermal stability, sensitivity to trypsin and periodate, and elution pattern in CM-Sephadex column chromatography. However, gel filtration pattern with Sephadex G-100 showed two separate peaks. Fractions collected from the first peak, corresponding to a molecular weight of about 45 000, had only the MIF activity, while those collected from the second peak, corresponding to a molecular weight of about 30 000, had both the interferon and MIF activities. A preparation of mouse brain interferon induced by Japanese encephalitis virus had a much weaker MIF activity than the L cell interferon, although these preparations were equal in interferon activity (5000 units/ml).     

Inhibition of Host-Cell Protein and Ribonucleic Acid Synthesis by Newcastle Disease Virus

The mechanisms of Newcastle disease virus-(NDV) induced inhibition of cell protein and ribonucleic acid (RNA) synthesis were investigated. It was observed that the ability of NDV to inhibit cell RNA synthesis is dependent on the virus strain. The inhibitors, azauridine and cycloheximide, were added to cell cultures at different times after infection to study the roles of protein and RNA synthesis in the viral inhibition process. Viral inhibition of cell RNA synthesis and viral inhibition of cell protein synthesis become resistant to cycloheximide at a different time after infection than that in which they become resistant to azauridine. The results indicate that the inhibition of cell RNA synthesis by the Texas strain involves the synthesis of inhibitory proteins which are coded by the viral genome. The Texas and Beaudette strains of NDV appear to employ different mechanisms for the inhibition of host-cell protein synthesis. Viral inhibition of cell protein synthesis does not appear to cause, or be the result of, viral inhibition of cell RNA synthesis.     

核糖体单链失活蛋白在无细胞体系中的活性

核糖体单链失活蛋白是一类广泛分布于植物中的蛋白质,它能使真核细胞核糖体60S亚基失活。本文报道了一些核糖体单链失活蛋白的制备、纯化以及在兔网织红细胞裂解液中对蛋白质生物合成的抑制活性及它们对完整细胞的毒性。其中多数的核糖体单链失活蛋白是首次被分离纯化并对其毒性进行研究的。     

Optimization of the Interferon Assay Using Inhibition of Semliki Forest Virus-Ribonucleic Acid Synthesis

The method for assaying chicken interferon by its inhibition of viral ribonucleic acid (RNA) synthesis was optimized for the chicken embryo fibroblast-Semliki Forest virus (SFV) system, with respect to time, multiplicity of infection, and addition of actinomycin D and (3)H-uridine. Incorporation of (3)H into viral RNA is reproducible, and amounts to 10(4) to 2 x 10(4) counts per min per uninhibited culture per 1 muCi per 6 hr. The assay may be carried out in less than 1 day and is sensitive (0.05 units/ml) and exact (+/-20% of the mean titers on different days); it can be used for purification procedures as well.     

Inhibition of Polyuridylic Acid-Directed Protein Synthesis by Aurintricarboxylate in Extracts of Escherichia coli

Aurintricarboxylic acid (ATA) inhibits protein synthesis directed by polyuridylic acid. All steps tested are inhibited by ATA. We conclude that inhibition of polyphenylalanine formation is an additive effect of inhibition of various steps in the protein synthetic machinery.     

Inhibition of Host Deoxyribonucleic Acid Synthesis by T4 Bacteriophage in the Absence of Protein Synthesis

The requirement for phage protein synthesis for the inhibition of host deoxyribonucleic acid synthesis has been investigated by using a phage mutant unable to catalyze the production of any phage deoxyribonucleic acid. It has been concluded that the major pathway whereby phage inhibit host syntheses requires protein synthesis. The inhibition of host syntheses by phage ghosts is not affected by inhibitors of protein synthesis.     

Inhibition by Chloramphenicol of Chlorophyll and Protein Synthesis and Growth in Euglena gracilis

SYNOPSIS. Chloramphenicol inhibits growth of Euglena gracilis. It also interferes in the greening process by inhibiting protein synthesis (measured by leucine uptake), but RNA synthesis is essentially unafiected. The antibiotic acts on all cell fractions, but prefermtially inhibits the synthesis of plastid protein. Inhibition of chlorophyll synthesis is transitory and does not affect the self-reproduction system for chloroplast formation.     

Inhibition of Host Protein Synthesis During Infection of Escherichi coli by Bacteriophage T4: III. Inhibition by Ghosts

Deoxyribonucleic acid (DNA)-less T2 "ghosts" were prepared by osmotic shock and purified by KBr density gradient centrifugation. Escherichia coli B was treated with these ghosts in inorganic salts-glycerol medium to see which features of phage infection could be elicited by ghosts. At a multiplicity that was just sufficient to block induction of beta-galactosidase (EC 3.2.1.23), 89% of the bacteria were killed and the rates of ribonucleic acid (RNA) and DNA synthesis were about 10 to 15% of normal. However, protein synthesis was almost completely blocked but resumed after 30 min. During this period, it was possible to induce messenger RNA (mRNA) from the lactose operon, although this mRNA could not be translated into active beta-galactosidase. These results suggest to us that the viable cells surviving ghost infection synthesize nucleic acids at close to a normal rate but are temporarily blocked in protein synthesis. The continued formation of untranslated host mRNA mimics the pattern of bacterial synthesis just after whole-phage infection, and is consistent with the interpretation that the immediate block in the initiation of host translation by these viruses is due to their attachment.