The heavy form of elongation factor 1 in artemia salina embryos is functionally analogous to a complex of bacterial factors EF-Tu and EF-Ts

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.

Evidence for regulation of protein synthesis at the elongation step by CDK1/cyclin B phosphorylation

Eukaryotic elongation factor 1 (eEF-1) contains the guanine nucleotide exchange factor eEF-1B that loads the G protein eEF-1A with GTP after each cycle of elongation during protein synthesis. Two features of eEF-1B have not yet been elucidated: (i) the presence of the unique valyl-tRNA synthetase; (ii) the significance of target sites for the cell cycle protein kinase CDK1/cyclin B. The roles of these two features were addressed by elongation measurements in vitro using cell-free extracts. A poly(GUA) template RNA was generated to support both poly(valine) and poly(serine) synthesis and poly(phenylalanine) synthesis was driven by a poly(uridylic acid) template. Elongation rates were in the order phenylalanine > valine > serine. Addition of CDK1/cyclin B decreased the elongation rate for valine whereas the rate for serine and phenylalanine elongation was increased. This effect was correlated with phosphorylation of the eEF-1delta and eEF-1gamma subunits of eEF-1B. Our results demonstrate specific regulation of elongation by CDK1/cyclin B phosphorylation.

The elongation factor-1delta (EF-1delta) originates from gene duplication of an EF-1beta ancestor and fusion with a protein-binding domain

The molecular evolution of two components of elongation factor-1 (EF-1), EF-1beta and EF-1delta was analysed using the distance matrix, the maximum parsimony and the maximum likelihood methods, after careful alignment of protein and cDNA sequences. The topology of the phylogenetic trees obtained supports monophyly of plant EF-1beta and EF-1beta' sequences, and monophyly of higher eukaryotic animal EF-1beta and EF-1delta sequences. EF-1beta and EF-1delta are homologous in their C-terminal domain. EF-1delta, which emerged before arthropods, originates from a beta-type ancestor gene and fusion with a leucine zipper N-terminal motif. Plant EF-1beta and EF-1beta' correspond to paralogous genes whose ancestor was most likely duplicated before the emergence of monocotyledons and dicotyledons.

Biological characterization of various forms of elongation factor 1 from rabbit reticulocytes

Two forms of elongation factor 1 (EF-1) have been tested for a variety of biological functions. One form, EF-1H, is a high-molecular-weight aggregate (Mr greater than 500,000) containing four distinct polypeptides (alpha, beta, gamma, delta). The other form, EF-1 alpha, consists of a single polypeptide which is the same as the alpha subunit of EF-1H. Both EF-1 alpha and EF-1H function catalytically in binding Phe-tRNA to ribosomes, and in poly(U)-directed polyphenylalanine synthesis. The activity of EF-1 alpha is enhanced in polyphenylalanine synthesis by a complementary component, EF-1 beta delta. It is also shown that EF-1 beta delta can facilitate an exchange of EF-1 alpha-bound GDP for GTP. The EF-1 alpha dissociation constants for GDP and GTP were 0.47 and 0.55 microM respectively, while the EF-1H dissociation constants for GDP and GTP were 2.0 and 1.6 microM, respectively. Thus, while EF-1 alpha and EF-1H had approximately the same affinities for GDP and GTP, the EF-1 alpha dissociation constants were about fourfold lower than the EF-1H dissociation constants. Attempts to isolate complexes of EF-1 alpha or EF-1H with GTP and Phe-tRNA or with GTP, Phe-tRNA, and ribosomes were unsuccessful using either Millipore filters, gel filtration, or sucrose density gradients. The results presented in this report, along with studies from other laboratories, strengthen the hypothesis that the general mechanism of the elongation cycle is similar in eucaryotes and procaryotes.

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.

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.

Functional and structural studies on a tryptic fragment of eucaryotic elongation factor Tu from rabbit reticulocytes

Treatment of eucaryotic elongation factor Tu (eEF-Tu; Mr 53 000) with trypsin results in cleavage of the factor at at least two sites, one and probably both of which are located near the amino-terminal end of the polypeptide chain. The products after exposure of eEF-Tu to trypsin for 2 h is a single polypeptide of 43 000 daltons (eEF-Tut) and as yet unidentified polypeptides of Mr less than or equal to 5000. The presence of high glycerol concentrations of GDP in the reaction mixture markedly retards the rate of tryptic cleavage, while GTP has little effect. When eEF-Tu is bound to eucaryotic elongation factor Ts in an eEF-T complex, it is much more resistant to the action of trypsin. The loss of factor activity during tryptic digestion (as measured by its ability to bind aminoacyl-tRNA to 80S (ribosomes) is much slower than the rate of eEF-Tut formation, and 2-h digests containing only eEF-Tut are about 30% as active as the native enzyme. However, no ribosome-dependent activity is detectable after purification of eEF-Tut by ion-exchange chromatography, followed by gel filtration. Purified eEF-Tut binds guanine nucleotides, although with diminished activity compared with that of eEF-Tu. Amino-terminal sequence analyses of eEF-Tut reveal a striking sequence homology with the functionally related factor from Escherichia coli (EF-Tu). The first four residues of eEF-Tut, Gly-Ile-Thr-Ile, are identical with the first four residues of a 37 000-dalton tryptic fragment of E. coli EF-Tu, and other homologies are evident in the first twelve amino-terminal residues of the corresponding tryptic fragments.

Protein synthesis in artemia salina. Eucaryotic elongation factor eEF-Ts is a transphosphorylase

It is thought that eucaryotic elongation factor eEF-Ts catalyzes the replacement of GDP for GTP on eucaryotic elongation factor eEF-Tu. We have found that eEF-Ts displays a strong nucleoside diphosphate phosphotransferase activity. This transferase activity resides in a dimer molecule of a subunit molecular weight close to 30,000. The transfosforylating activity of eEF-Ts results in a stimulatory effect of ATP, GTP, UTP and CTP on protein synthesis provided that GDP is present. The specificity for guanine nucleotides in protein synthesis resides only in eEF-Tu.

Eucaryotic elongation factors Ts is an integral component of rabbit reticulocyte elongation factor 1

Elongation factor 1 (EF-1) was purified from rabbit reticulocytes and found to contain at least two distinct polypeptides: one of Mr 53 000 and one of Mr 30 000. The 30 000-Mr polypeptide was purified from EF-1 by treatment of the factor with 5.4 M guanidine . HCl and subsequent chromatography on DEAE-BioGel A in the presence of 5 M urea. By a number of functional criteria, the 30 000-Mr polypeptide was found to be the eucaryotic elongation factor Ts (eEF-Ts). These criteria include the ability of the polypeptide to stimulate Artemia salina eEF-Tu-dependent binding of aminoacyl-tRNA to 80-S ribosomes as well as eEF-Tu + EF-2-dependent polyphenylalanine synthesis. The reticulocyte factor also markedly increased the rate of exchange of eEF-Tu . gdp complexes with free GTP. Furthermore, rabbit antibodies to EF-1 from A. salina which was previously shown to contain eEF-Ts [Slobin, L. I. and Möller, W. (1978) Eur. J. Biochem. 84, 69--77] were found to cross-react with reticulocyte eEF-Ts, suggesting extensive structural homology between brine shrimp and rabbit eEF-Ts. The demonstration that eEF-Ts is and integral component of EF-1 from such diverse sources as brine shrimp and rabbit reticulocytes supports the conclusion that the factor is universally present in eucaryotic EF-1.

The role of guanine nucleotides in the interaction between aminoacyl-tRNA and elongation factor 1 of Artemia salina

The low-molecular-weight form of elongation factor 1 (EF-1L) of the cysts of the brine shrimp Artemia salina and [3H]phenylalanyl-tRNA are able to form a stable complex which can be isolated on a Sephacryl S200 column. The formation of this complex is inhibited by increasing concentrations of magnesium acetate and KCl. Furthermore, the formation of this complex is independent of the presence of guanine nucleotides. Complex formation between EF-1L and phenylalanyl-tRNA appears to be specific, since acylation of the tRNA is a necessity for this interaction. Although EF-1L alone binds GDP somewhat more strongly than GTP, the complex between EF-1L and phenylalanyl-tRNA binds GTP exclusively. Our results support the idea that complex formation between EF-1L and aminoacyl-tRNA precedes the enzymatic binding of aminoacyl-tRNA to the 80-S ribosome. Subsequently to this binding, release of EF-1L from the ribosome occurs.

Binding of reticulocyte elongation factor 1 to ribosomes and nucleic acids

The present study has examined the requirements for the binding of rabbit reticulocyte elongation factor 1 (EF-1) to ribosomes under different assay conditions. When a centrifugation procedure was used to separate the ribosome EF-1 complex, the binding of EF-1 to ribosomes required GTP and Phe-tRNA, but not poly(U). The results suggested that undr these conditions a ternary complex, EF-1 . GTP . aminoacyl-tRNA, is necessary for the formation of a ribosome . EF-1 complex. However, when gel filtration was used to isolate the ribosome . EF-1 complex, only template and tRNA were required. These studie emphasize the fact that the procedure used to isolate the ribosome . EF-1 complex determines the requirements for stable complex formation. EF-1 can also interact with nucleic acids such as 28 S and 18 S rRNA, messenger RNA and DNA. In contrast to the binding to ribosomes, EF-1 binding to nucleic acids requires only Mg2+.

Further evidence that elongation factor 1 remains bound to ribosomes during peptide chain elongation

This paper describes three types of experiments which indicate that the binding sites for elongation factor 1 (EF-1) and elongation factor 2 (EF-2) on ascites cell ribosomes are not identical and perhaps not even overlapping. The experimental evidence presented includes direct competitive binding of labeled elongation factors to ribosomes as well as the influence of pokeweed antiviral protein and Escherichia coli anti L7/L12 proteins on the binding and function of the two factors. It is further shown that EF-1beta from Artemia salina does not function in displacing EF-1 from mouse ascites tumor cell ribosomes. These results also support our recently proposed model that EF-1 remains bound to the ribosome during the peptide chain elongation cycle.