Changes in form of elongation factor during development of Artemia salina

eEF1B: At the dawn of the 21st century

Translational regulation of gene expression in eukaryotes can rapidly and accurately control cell activity in response to stimuli or when rapidly dividing. There is increasing evidence for a key role of the elongation step in this process. Elongation factor-1 (eEF1), which is responsible for aminoacyl-tRNA transfer on the ribosome, is comprised of two entities: a G-protein named eEF1A and a nucleotide exchange factor, eEF1B. The multifunctional nature of eEF1A, as well as its oncogenic potential, is currently the subject of a number of studies. Until recently, less work has been done on eEF1B. This review describes the macromolecular complexity of eEF1B, its multiple phosphorylation sites and numerous cellular partners, which lead us to suggest an essential role for the factor in the control of gene expression, particularly during the cell cycle.

Eukaryotic translation elongation factor 1 alpha: structure, expression, functions, and possible role in aminoacyl-tRNA channeling

This review offers a comprehensive analysis of eukaryotic translation elongation factor 1 (eEF-1 alpha) in comparison with its bacterial counterpart EF-Tu. Altogether, the data presented indicate some variances in the elongation process in prokaryotes and eukaryotes. The differences may be attributed to translational channeling and compartmentalization of protein synthesis in higher eukaryotic cells. The functional importance of the EF-1 multisubunit complex and expression of its subunits under miscellaneous cellular conditions are reviewed. A number of novel functions of EF-1 alpha, which may contribute to the coordinate regulation of multiple cellular processes including growth, division, and transformation, are characterized.

Valyl-tRNA synthetase from Artemia. Purification and association with elongation factor 1

Two components of the protein biosynthetic machinery, valyl-transfer RNA synthetase (VRS) and elongation factor 1 (EF-1), have been isolated as a complex from several mammalian tissues. However, yeast VRS, which lacks an amino-terminal extension, does not associated with EF-1. We purified VRS from the brine shrimp Artemia and investigated its interaction with EF-1. Western blotting of crude Artemia extracts revealed the presence of two forms of VRS, differing in size and capacity to associate with EF-1. About 80% of the total VRS corresponds to a polypeptide of 130 kDa which behaves as a monomer upon gel filtration. Only the larger form of 140 kDa coelutes, cosediments and co-immunoprecipitates with the EF-1 alpha 2 beta gamma delta complex. The ratio of the two forms of VRS remains constant throughout early development. The possible origin and mode of expression of the two forms of VRS present in Artemia are discussed.

Peptide-chain elongation in eukaryotes

The elongation phase of translation leads to the decoding of the mRNA and the synthesis of the corresponding polypeptide chain. In most eukaryotes, two distinct protein elongation factors (eEF-1 and eEF-2) are required for elongation. Each is active as a complex with GTP. eEF-1 is a multimer and mediates the binding of the cognate aminoacyl-tRNA to the ribosome, while eEF-2, a monomer, catalyses the movement of the ribosome relative to the mRNA. Recent work showing that bacterial ribosomes possess three sites for tRNA binding and that during elongation tRNAs may occupy 'hybrid' sites is incorporated into a model of eukaryotic elongation. In fungi, elongation also requires a third factor, eEF-3. A number of mechanisms exist to promote the accuracy or 'fidelity' of elongation: eEF-3 may play a role here. cDNAs for this and the other elongation factors have been cloned and sequenced, and the structural and functional properties of the elongation factors are discussed. eEF-1 and eEF-2 can be regulated by phosphorylation, and this may serve to control rates of elongation in vivo.

Elongation factor 1 beta gamma from Artemia. Purification and properties of its subunits

The guanine nucleotide exchange factor, elongation factor 1 beta gamma (EF-1 beta gamma) has been purified from Artemia cysts using an improved method. The protein consists of two distinct polypeptides with relative molecular masses of 26,000 (EF-1 beta) and 46,000 (EF-1 gamma). A nucleoside diphosphate phosphotransferase activity often found in EF-1 beta gamma preparations has been completely separated from the actual guanine nucleotide exchange stimulatory activity of EF-1 beta gamma, thus indicating that nucleotide diphosphate phosphotransferase is not an intrinsic property of EF-1 beta. Both EF-1 beta gamma and EF-1 beta have been shown to stimulate the following three reactions to a comparable degree: (a) exchange of GDP bound to EF-1 alpha with exogenous GDP; (b) EF-1 alpha-dependent binding of Phe-tRNA to ribosomes; (c) poly(U)-dependent poly(phenylalanine) synthesis. However, a significantly higher nucleotide exchange rate was observed in the presence of EF-1 beta gamma compared to EF-1 beta alone. Concerning elongation factor 1 gamma (EF-1 gamma) the following observations were made. In contrast to EF-1 beta, pure EF-1 gamma is rather insoluble in aqueous buffers, but the tendency to precipitate can be partially suppressed by the addition of detergents. In particular, EF-1 gamma partitions solely into the detergent phase of Triton X-114 solutions. EF-1 gamma is also more susceptible to spontaneous, specific fragmentation. It is remarkably that about 5% of the cellular pool of EF-1 beta gamma was found to be present in membrane fractions, under conditions where no EF-1 alpha was detectable in these fractions. Furthermore it was noted that EF-1 beta gamma copurified strongly with tubulin on DEAE-cellulose. Moreover, it was observed that from a mixture of EF-1 beta gamma and tubulin, EF-1 gamma coprecipitates with tubulin using a non-denaturating immunoprecipitation technique. These findings suggest that EF-1 gamma has a hydrophobic domain and interacts with membrane and cytoskeleton structures in the cell.

Characterization of the elongation factors from calf brain. 2. Functional properties of EF-1 alpha, the action of physiological ligands and kirromycin

The properties of EF-1 alpha from calf brain have been investigated and compared with those of EF-Tu. EF-1 alpha binds GDP and GTP in a 1:1 stoichiometry, showing the same affinity for both nucleotides (K'd = 2-4 microM). EF-1 beta strongly enhances the dissociation rate of the EF-1 alpha X GDP complex and to a lesser extent of the EF-1 alpha X GTP complex. Aminoacyl-tRNA (aa-tRNA) stabilized EF-1 alpha X GTP much less efficiently than the EF-Tu X GTP complex. Unlike EF-Tu, EF-1 alpha sustains the binding of aa-tRNA to the ribosome also in the presence of GDP or in the absence of any nucleotide, though to a lesser degree than with GTP. Kirromycin enhances the dissociation rate of both EF-1 alpha X GTP and EF-1 alpha X GDP but especially that of the latter. This effect results in an increase of the exchange rate of the EF-1 alpha-bound nucleotide with free nucleotides. Although in this regard the effect of kirromycin mimics that of EF-1 beta, the antibiotic is incapable of increasing the EF-1 alpha X GDP/GTP exchange rate when aa-tRNA and ribosomes are present. Therefore, unlike EF-1 beta, kirromycin cannot enhance the rate of poly(Phe) synthesis. On the other hand, the failure of kirromycin to induce a GTP-like conformation of EF-1 alpha X GDP, as in the case of EF-Tu X GDP, explains its inability to inhibit peptide bond formation in the eukaryotic system.

Influence of fasting and refeeding on the elongation step of protein synthesis in rat liver of young (3M) and aging (18M) animals

The in vitro binding capacity for AA-tRNA of ribosomes, catalysed by EF1 enzyme, was studied in livers of rats, which had been starved for 5 days and re-fed for 3, 9, and 24 hours. The experiments were carried out with 3 and 18-month-old rats. The results were compared to those obtained with normally fed rats of the same ages. For both age groups, there was a similar change in the binding capacity, including a return to normal values after 24 hours of refeeding. When ribosomes of old control animals were treated with different enzymes, we obtained lower binding activities for all the experimental groups than in homologous cell-free systems (ribosomes and EF1 isolated from the same group). The ribosomes of young animals, tested in the presence of different enzymes, display an increased binding capacity, when the enzymes used were those of old (control and re-fed) animals. The recovery of the catalytic activity of EF1 on the binding process was observed after 9 hours in old animals, whereas it was not seen for young re-fed animals at that time of refeeding. EF1 seems to play an important role in the adaptation of older animals to fasting and refeeding.

Purification of various forms of elongation factor 1 from rabbit reticulocytes

Previous studies have indicated that the high-molecular-weight form of elongation factor 1 (EF-1H) contained four subunits (alpha, beta, gamma, and delta). Using the conventional methods of gel-filtration and ion-exchange chromatography, various forms of elongation factor 1 (EF-1 alpha, EF-1 beta delta, EF-1 beta gamma delta) have been purified from rabbit reticulocyte lysate. The procedure described allows one to purify these factors from a single batch of lysate in sufficient amounts for physical and biochemical studies. EF-1 alpha is a single polypeptide of Mr 52,000, and has an isoelectric point of 9.1. EF-1 beta delta and EF-1 beta gamma delta are composed of two and three nonidentical polypeptides, respectively, as judged by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Both proteins can form stable aggregates in native conditions that can reach more than 2,000,000 Da. The isoelectric point for each polypeptide was determined; 5.8 for EF-1 beta, 5.5 for EF-1 gamma, and 4.8 for EF-1 delta. The activity of both proteins was compared on a molecular basis by their ability to stimulate EF-1 alpha in the poly(U)-directed synthesis of polyphenylalanine. On the basis of this assay EF-1 beta gamma delta is slightly more active than EF-1 beta delta. The similarity of the amino acid composition of EF-1 gamma and EF-1 delta and the molar ratio of alpha: beta: gamma: delta in EF-1H of approximately 1:1:0.5:0.5 have led to the conclusion that EF-1 delta is probably a breakdown product of EF-1 gamma, and that the native form of EF-1H probably contains only the alpha, beta, and gamma subunits.

Changes in form of elongation factor 1 during germination of wheat seeds

Two forms of EF-1 are present in the high-speed supernatant fraction from wheat embryo homogenate. In embryos from dry seeds EF-1H is 55% of the total amount of EF-1, while after 40 h of germination this form completely disappears. When germination and protein synthesis are accelerated by means of 6-benzyladenine, the rate of conversion of EF-1H is increased. On the other hand, the block of germination and of the evolution of protein synthesis by abscisic acid, block this conversion; the block of water uptake, that stops germination and causes a decrease in protein synthesis, reverses the conversion of EF-1H to EF-1L, increasing EF-1H from 15% to 40% of the total.

Methylation of elongation factor 1 alpha in mouse 3T3B and 3T3B/SV40 cells

Two-dimensional gel electrophoretic (NEPHGE) analysis of proteins from mouse 3T3B and 3T3B/SV40 cells labelled with [methyl-3H]methionine in the presence of cycloheximide have revealed that the elongation factor 1 alpha (EF-1 alpha) in these cells is methylated and that the extent of methylation is higher in the SV40 transformed cell type. It is suggested that methylation may account for differences in growth properties for the different cell types.

A poly(U)-binding factor stimulating EF-1 activity in the wheat-germ soluble fraction

A poly(U)-binding activity is present in the high-speed supernatant fraction of embryo homogenates from wheat seeds. The factor responsible for such activity was found to have a stimulatory effect on the elongation factor 1 (EF-1). It copurifies with EF-1L, the lighter form of EF-1, through Sephadex G-200, DEAE-cellulose, hydroxyapatite and poly(U)-Sepharose 4B column chromatography. The two factors could be separated only through a heating step which destroyed EF-1 activity whilst leaving most of the poly(U)-binding activity unaltered.

Sequence homology between EF-1 alpha, the alpha-chain of elongation factor 1 from Artemia salina and elongation factor EF-Tu from Escherichia coli

In the course of a structural analysis of the alpha-chain of elongation factor 1 from Artemia salina cysts, we present four amino acid sequences comprising together half of the polypeptide chain. A comparison of these sequences with the primary structure of elongation factor EF-Tu from Escherichia coli reveals a clear correspondence between the eukaryotic and prokaryotic protein throughout their polypeptide chains. The results support a basic conservation of the structure of the aminoacyl-tRNA carrying enzyme in evolution. The occurrence, in the eukaryotic factor, of several epsilon-trimethyllysine residues, is remarkable.

Polypeptide elongation factors of the developing chick brain

The polypeptide elongation factors (EF-1L, EF-1H, and EF-2) of the developing chick brain were separated and purified by means of a combination of gel chromatographic methods. The molecular weight of EF-1H of the chick brain ranged from 5 to 10 x 10(5), and was different from that of the chick liver (about 7 x 10(5). The molecular weight of other purified factors was about 5 x 10(4) for EF-1L and 9.4 x 10(4) for EF-2. High activities of polyphenylalanine (poly-Phe) synthesis per mg protein in the developing chick brain were observed between the 3rd embryonic week and the 1st post-hatch week and declined afterwards. On the other hand, the levels of both EF-1 and EF-2 per mg protein in the brain were observed to be high in an early embryonic stage, gradually declining afterwards to the adult level. The brain EF-1L was a major component of EF-1 in an early embryonic stage, while EF-1H became recognizable in the 3rd embryonic week. Moreover, the EF-1H activities were found to be more than double with regard to the binding reaction and to be more than 10-fold as active in respect to poly-Phe synthesis in comparison with the activities of EF-1L. It is proposed that the brain EF-1H could be due to aggregates consisting of Ef-1L, a stimulatory factor, and other components.

Partial purification of the messenger RNA for eukaryotic elongation factor Tu from Artemia salina

Polyadenylated RNA from developing Artemia salina cysts was fractionated by centrifugation through a sucrose gradient containing methylmercuric hydroxide (CH3HgOH). Aliquots of each fraction were directly added to a rabbit reticulocyte lysate to program protein synthesis in vitro. The translation products were assayed for eukaryotic elongation factor Tu (eEF-Tu) by immunoprecipitation with an antibody raised in rabbits and purified by affinity chromatography. The immunoprecipitated radioactivity was analyzed by polyacrylamide gel electrophoresis in the presence of sodium dodecylsulphate. Sequences coding for eEF-Tu sediment in the 20-S region of the gradient and form a major component of the poly(A)-containing RNA. The mRNA of the 20-S region, comprising about 10% of the poly(a)-containing RNA fractionated on the gradient, has been translated in vitro and 30% of the translation products represent immunoprecipitable eEF-Tu protein chains with an Mr of 50000.

Role of elongation factor 1 in the translational control of rodent brain protein synthesis

The translational control of protein synthesis during early postnatal neural development and aging was examined in the mouse and the rat. The activity of brain elongation factor 1 (bEF-1) was found to decrease exponentially with age and to decline parallel to the age-dependent decrease in total protein synthesis in both rodents. This decrement in bEF-1 activity fell within the range of reported age-related decreases in protein synthesis in in vitro systems. The factor was present in multiple forms; the lighter species predominated in older animals, whereas the young light form apparently disappeared with increasing age, and was replaced by other arising from the heavy form. Elongation factor 1 derived from young brains functioned as a rate-limiting component in polypeptide synthesis in previously saturated adult systems. The data suggest that bEF-1 has an important modulatory effect on total brain protein synthesis.

Interrelationships between water and cellular metabolism in Artemia cysts. VI. RNA and protein synthesis

Using 14CO2 as a labelled precursor the relationship between the initiation of protein and RNA synthesis, and water concentration, has been examined in cysts (encysted embryos) of the brine shrimp, Artemia salina. Although incorporation of radioactivity into amino acids and nucleotides occurred in cysts at hydrations as low as 0.3 g H2O/g dried cysts, incorporation into proteins and RNA was not measurable until the cysts had achieved a hydration in the range of 0.6-0.6 g/g. In no case was radioactivity detected in DNA of unemerged cysts. Fully hydrated cysts (about 1.3 g/g) that were actively synthesizing proteins and RNA, stopped doing so when dehydrated to levels below the same hydration range: thus, the hydration dependence does not involve appreciable hysteresis. The hydration range required to initiate synthesis of these macromolecules is essentially the same as that previously shown to initiate embryonic development.

The translation in vitro of mRNA from developing cysts of Artemia salina

Successive stages in the development of the brine shrimp cyst were used as a model for studying differentiation at the level of mRNA transcription and translation. The poly (A)-containing mRNA from dormant cysts and free-swimming larvae (nauplii) was found to be efficiently translated in a wheat-germ cell-free system, and electrophoretic patterns of translation products in vitro resembled those of the endogenous proteins extracted from the equivalent developmental stages. Each stage, however, exhibits a characteristic protein pattern. Two low-molecular-weight proteins prominent in the cyst disappeared almost completely in the nauplius stage, whereas the proportion of actin increased 3-fold. Parallel patterns were observed upon translation in vitro of the respective mRNA preparations. The percentage of the acidic protein, tubulin, decreased somewhat during development.

Regeneration of renal proximal tubules after mercuric chloride injury is accompanied by increased binding of aminoacyl-transfer ribonucleic acid

Homogenates of rat kidney cortex obtained 1,3 or 14 days after a single injection of HgCl2 were used to prepare the post-microsomal pH5 supernatant fraction. The activity of this fraction for peptide synthesis from [14C]phenylalanyl-tRNA was significantly increased at 1 and 3 days, at which time the proximal tubules are regenerating [Cuppage & Tate (1967) Am. J. Pathol. 51, 405-429]. This increased activity could not be attributed to a decreased inhibitory activity, but was due to an increased aminoacyl-tRNA binding, i.e. elongation-factor-1 activity, in the supernatant fraction.

Functional identity of the monomeric and multiple forms of elongation-factor 1 from Krebs-II mouse ascites-tumor cells

Highly purified 3H-labelled elongation factor 1 (EF-1) from Krebs II mouse ascites tumour cells was separated into biologically active monomeric and aggregate forms of the enzyme by either gradient centrifugation or gel filtration. When corrected for their content of inactive enzyme both forms of the factor were found to be equally active whether tested in the binding or synthesis reaction. The only form of the enzyme found bound to ribosomes was the monomer; it was therefore concluded that the aggregate form of the enzyme must first dissociate before it reacts with the ribosome. The stoichiometry of the aminoacyl-tRNA binding reaction to ribosomes in the presence of guanosine nucleotides was also studied. It was found that one molecule of aminoacyl-tRNA and of Guo-5'-P2-CH2-P is bound per molecule of EF-1 bound to the ribosome. Following interaction with a release from, the ribosomes, EF-1 was found to be predominantly monomeric.

Protein synthesis in dystrophic muscle. Activity of the pH 5 supernatant fraction of muscle in dystrophic mice

The pH 5 supernatant fractions prepared from homogenates of tissues of normal and dystrophic mice were used to study the incorporation of [14C]phenylalanyl-tRNA into peptide. The incorpoation was markedly reduced using the muscle pH 5 supernatant fraction from dystrophic animals but no reduction was seen with brain, liver or heart preparations from dystrophic mice. The lower incorporation with dystrophic muscle pH 5 supernatant was not due to altered activity of ribonuclease, elongation factors, proteolytic enzymes, GTP or sulfhydryl reagents, but was attributable to the presence of activity that was inhibitory to protein synthesis.

Elongation factor 1 from Artemia salina: properties and disaggregation of the enzyme

Elongation factor 1 has been purified from undeveloped embryos of Artemia salina. The purified enzyme appears to be an aggregate (molecular weight approximately to 200 000) which on sodium dodecylsulfate gels shows the presence of two major protein bands whose estimated molecular weights are 52 000 and 47 000. Lipid material appears to be associated with the purified protein. In aminoacyl-tRNA binding to ribosomes, there is only a limited turnover of the enzyme, but the protein acts catalytically in amino acid polymerization. The enzyme is disaggregated by a partially purified phospholipase C preparation, elastase and under certain conditions, by guanosine nucleotides. The significance of these results is discussed with respect to the overall role of elongation faction 1 in aminoacyl-tRNA binding to ribosomes.