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J M Ravel

Publications and source records attributed to J M Ravel.

At least 37 records · Page 2Linked to original sources
PubMed1986

ATPase activities of wheat germ initiation factors 4A, 4B, and 4F.

Eukaryotic initiation factors (eIF)-4A, -4B, and -4F isolated from wheat germ were tested for their ability to catalyze ATP hydrolysis in the absence and presence of RNA. We find that eIF-4B or eIF-4F alone exhibit ATPase activity in the presence of poly(U), satellite tobacco necrosis virus (STNV) RNA, or globin mRNA but not in the absence of RNA. eIF-4A alone exhibits ATPase activity in the absence of RNA, but this activity is not stimulated by the addition of RNA. eIF-4A does, however, enhance RNA-dependent ATP hydrolysis in the presence of either eIF-4B or eIF-4F. The RNA-dependent ATPase activities of eIF-4B and eIF-4F are additive, not synergistic. At saturating concentrations of eIF-4F, little or no stimulation of ATP hydrolysis is obtained upon the addition of eIF-4B and at saturating concentrations of eIF-4B little or no stimulation is obtained upon the addition of eIF-4F. This observation is in agreement with our previous finding (Lax, S., Fritz, W., Browning, K., and Ravel, J. (1985) Proc. Natl. Acad. Sci. U.S.A. 82, 330-333) that initiation of polypeptide synthesis is obtained in vitro with either eIF-4F or eIF-4B.

Adenine Nucleotides↗
PubMed1986

Interaction of turnip yellow mosaic virus Val-RNA with eukaryotic elongation factor EF-1 [alpha]. Search for a function.

The 3'-terminal tRNA-like structure in turnip yellow mosaic virus (TYMV) RNA can be adenylated by tRNA nucleotidyltransferase and subsequently aminoacylated by valyl-tRNA synthetase. Here we present evidence that TYMV Val-RNA can form a stable complex with eukaryotic wheat germ elongation factor EF-1alpha and GTP: the Val-RNA is protected by EF-1alpha.. GTP against digestion by RNase A. By affinity chromatography of TYMV Val-RNA fragments on immobilized EF-1alpha . GTP, it has been established that the valylated aminoacyl RNA domain, which in TYMV RNA is formed by the 3' half of the tRNA-like region, is sufficient for complex formation with EF-1alpha . GTP. The aminoacyl RNA domain is equivalent in tRNAs to the continuous helix formed by the acceptor stem and the T stem and loop. In line with these results, the aminoacyl RNA domain in TYMV Val-RNA complexed to EF-1 alpha . GTP is resistant to digestion by RNase A. It is also shown that the TYMV RNA replicase (RNA-dependent RNA polymerase) isolated from TYMV-infected Chinese cabbage leaves does not contain tRNA nucleotidyltransferase, valyl-tRNA synthetase or EF-1alpha. This suggests that interaction of TYMV RNA with EF-1alpha is not mandatory for replicase activity.

Base Sequence↗
PubMed1985

Characterization of initiation factor 3 from wheat germ. 1. Effects of proteolysis on activity and subunit composition.

Wheat germ initiation factor 3 (eIF-3) is a large (15 S) particle containing 10 subunits with molecular weights ranging from 28 000 to 116 000. Two forms of wheat germ eIF-3 which differ in ability to support polypeptide synthesis in vitro have been obtained by chromatography on carboxymethyl-Sephadex (CM-Sephadex). The less active form is not retained on CM-Sephadex in 50 mM KCl and contains lower amounts of two subunits, the 116 000-dalton polypeptide (pp116) and the 36 000-dalton polypeptide (pp36). The more active form is retained on CM-Sephadex in 50 mM KCl and is eluted by 150 mM KCl. Treatment of the more active form with small amounts of trypsin results in a rapid degradation of four of the subunits (pp116, pp107, pp87, and pp36) and in a rapid loss in the ability to support polypeptide synthesis. Trypsin treatment also diminishes the ability of eIF-3 to support the binding of mRNA to 40S ribosomal subunits. These findings indicate that pp116, pp107, pp87, and pp36 are in exposed positions in the eIF-3 particle and that pp116 and/or pp36 are essential for activity.

Eukaryotic Initiation Factor-3↗
PubMed1985

Characterization of initiation factor 3 from wheat germ. 2. Effects of polyclonal and monoclonal antibodies on activity.

Rabbit polyclonal antibodies to wheat germ initiation factor 3 (eIF-3) were obtained and were shown to react strongly with 4 of the 10 subunits of eIF-3 (pp116, pp87, pp56, and pp36). Two mouse monoclonal antibodies were obtained, one of which reacts specifically with pp87 and one of which reacts specifically with pp36. Highly purified anti-pp87 has no effect on the activity of eIF-3. Highly purified polyclonal antibodies and anti-pp36 inhibit the ability of eIF-3 to support polypeptide synthesis in vitro and the ability of eIF-3 to support mRNA binding to 40S ribosomal subunits. These results provide additional evidence that pp116, pp87, and pp36 are in exposed positions in the eIF-3 particle and that pp36 is essential for activity.

Antibodies↗
PubMed1985

Phosphorylation of wheat germ initiation factors and ribosomal proteins.

The ability of the wheat germ initiation factors and ribosomes to serve as substrates for a wheat germ protein kinase (Yan and Tao 1982 J Biol Chem 257: 7037-7043) has been investigated. The wheat germ kinase catalyzes the phosphorylation of the 42,000 dalton subunit of eukaryotic initiation factor (eIF)-2 and the 107,000 dalton subunit of eIF-3. Other initiation factors, eIF-4B and eIF-4A, and elongation factors, EF-1 and EF-2, are not phosphorylated by the kinase. Quantitative analysis indicates that the kinase catalyzes the incorporation of about 0.5 to 0.6 mole of phosphate per mole of the 42,000 dalton subunit of eIF-2 and about 6 moles of phosphate per mole of the 107,000 dalton subunit of eIF-3. Three proteins (M(r) = 38,000, 14,800, and 12,600) of the 60S ribosomal subunit are phosphorylated by the kinase, but none of the 40S ribosomal proteins are substrates of the kinase. No effects of phosphorylation on the activities of eIF-2, eIF-3, or 60S ribosomal subunits could be demonstrated in vitro.

Journal Article↗
PubMed1984

Purification and characterization of three elongation factors, EF-1 alpha, EF-1 beta gamma, and EF-2, from wheat germ.

Three elongation factors, EF-1 alpha, EF-1 beta gamma and EF-2, have been isolated from wheat germ. EF-1 alpha and EF-2 are single polypeptides with molecular weights of approximately 52,000 and 102,000, respectively. The most highly purified preparations of EF-1 beta gamma contain four polypeptides with molecular weights of approximately 48,000, 46,000 and 36,000, 34,000. EF-1 alpha supports poly(U)-directed binding of Phe-tRNA to wheat germ ribosomes and catalyzes the hydrolysis of GTP in the presence of ribosomes, poly(U), and Phe-tRNA. EF-2 catalyzes the hydrolysis of GTP in the presence of ribosomes alone and is ADP-ribosylated by diphtheria toxin to the extent of 0.95 mol of ADP-ribose/mol of EF-2. EF-1 beta gamma decreases the amount of EF-1 alpha required for polyphenylalanine synthesis about 20-fold. EF-1 beta gamma enhances the ability to EF-1 alpha to support the binding of Phe-tRNA to the ribosomes and enhances the GTPase activity of EF-1 alpha. Wheat germ EF-1 alpha, EF-1 beta gamma, and EF-2 support polyphenylalanine synthesis on rabbit reticulocyte ribosomes as well as on yeast ribosomes.

Kinetics↗
PubMed1983

Factors from wheat germ that enhance the activity of eukaryotic initiation factor eIF-2. Isolation and characterization of Co-eIF-2 alpha.

Two factors have been isolated from wheat germ that enhance the ability of initiation factor 2(eIF-2) to form a ternary complex with GTP and Met-tRNAf. One of these factors, Co-eIF-2 beta, is a monomeric protein with a molecular weight of approximately 83,000 (Lax, S. R., Osterhout, J.J., and Ravel, J.M. (1982) J. Biol. Chem. 257, 8233-8237). The purification and properties of Co-eIF-2 alpha are described in this report. The most highly purified preparations of Co-eIF-2 alpha contain two polypeptides with molecular weights of 21,000 and 19,000. Both Co-eIF-2 alpha and Co-eIF-2 beta are heat-stable factors that stimulate ternary complex formation in the presence and absence of Mg2+ and overcome the inhibitory effect of aurintricarboxylic acid. Co-eIF-2 alpha differs from Co-eIF-2 beta in that Co-eIF-2 beta stimulates the formation of a binary complex between eIF-2 and GDP and Co-eIF-2 alpha does not. Also. The stimulatory effects of Co-eIF-2 alpha and Co-eIF-2 beta on the ternary complex formation are close to additive, strongly suggesting that the two factors function independently. Neither Co-eIF-2 alpha nor Co-eIF-2 beta enhances the rate of exchange between GDP bound to eIF-2 and free GDP, indicating that neither factor functions as a guanine nucleotide exchange factor.

Eukaryotic Initiation Factor-2↗
PubMed1982

Factors from wheat germ that enhance the activity of eukaryotic initiation factor eIF-2. Isolation and characterization of Co-eIF-2 beta.

A factor has been isolated from wheat germ that enhances the ability of initiation factor 2 (eIF-2) to form a ternary complex with GTP and Met-tRNAf and enhances the binding of Met-tRNAf to 40 s ribosomal subunits. This factor, designated Co-eIF2 beta, is a monomeric protein with a molecular weight of approximately 83,000. Wheat germ eIF-2 forms a stable binary complex with GDP but not with GTP. Co-eIF-2 beta enhances the formation of an eIF-2 . GDP complex, but does not enable eIF-2 to form a stable complex with GTP.

Eukaryotic Initiation Factor-2↗
PubMed1981

Characterization of initiation factor eIF-3 from wheat germ.

Initiation factor eIF-3 has been isolated from the 120 mM KCl postribosomal supernatant of wheat germ by chromatography on DEAE-cellulose and phosphocellulose. Glycerol gradient centrifugation and polyacrylamide gel electrophoresis under nondenaturing conditions indicate that the eIF-3 prepared in this manner is at least 85% pure. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate shows that the wheat germ eIF-3 contains 11 polypeptides, ranging in molecular weight from about 25,000 to 120,000. Eight of the polypeptides are present in equimolar amounts; two of the polypeptides are present at molar ratios of about 0.5; and one is present at a molar ratio of about 0.3. The highly purified wheat germ eIF-3 does not prevent the association of wheat germ 40S and 60 S ribosomal subunits to a significant extent. Wheat germ eIF-3 does not increase appreciably the ability of eIF-2 to form a ternary complex with Met-tRNAf and GTP. It does, however, enhance the binding of Met-tRNAf to 40 S ribosomal subunits in the presence of eIF-2 and GTP.

Eukaryotic Initiation Factor-3↗
PubMed1977

Repression of the tyrosine, lysine, and methionine biosynthetic pathways in a hisT mutant of Salmonella typhimurium.

A comparison was made of the repressibility of certain enzymes in the tyrosine, methionine, and lysine biosynthetic pathways in wild-type Salmonella typhimurium and a hisT mutant. The results show that (i) tyrosine represses the synthesis of the tyrosine-sensitive 3-deoxy-D-arabino-heptulsonic acid 7-phosphate synthetase and the tyrosine aminotransferase to the same extent in a hisT mutant as in wild type and (ii) there is no detectable alteration in the extent to which methionine represses O-succinylhomoserine synthetase or in the extent to which lysine represses the lysine-sensitive beta-aspartokinase as a result of the hisT mutation.

2-Isopropylmalate Synthase↗
PubMed1976

Evidence for an extrinsic immunogen in effective ribosomal vaccines from Salmonella typhimurium.

Previous work has indicated that ribosomes isolated from Salmonella typhimurium were highly immunogenic and afforded excellent protection against homologous challenge. Effective protection was obtained also when ribonucleic acid ( RNA) extracted from these ribosomes was used as a vaccine. In this investigation ribosomes prepared by another method and washed repeatedly in 1 M NH1Cl lost much of their prophylactic potency and yielded poorly protective RNA. The high-salt wash of the ribosomes was immunogenic. The RNA and the protein isolated from the salt wash of the ribosomes were effective vaccines. No intrinsic component of the ribosomes was removed by the NH4Cl wash, since the ability of both "crude" and "clean" ribosomes to function equally well in an in vitro protein synthesizing system was demonstrated. The presence of a component with toxic properties similar to those of endotoxin was found in active vaccines but not in weak ones. This was shown by the ability of effective vaccines to kill lead acetate-sensitized mice and to induce tolerance to endotoxin.

Animals↗