Elongation factor 1 from the silk gland of silkworm. Purification and some properties of its gamma subunit having EF-1b activity

Toxicity of two type II ribosome-inactivating proteins (cinnamomin and ricin) to domestic silkworm larvae

Cinnamomin and ricin are two type II ribosome-inactivating proteins. They exhibited a different toxicity to domestic silkworm (Bombyx mori) larvae by oral feeding bioassay. The LC50 of ricin to the silkworm larvae at third instar was much lower than that of cinnamomin. When the isolated 80S ribosome from domestic silkworm pupae was treated separately with the reduced cinnamomin or the reduced ricin, a specific RNA fragment (R-fragment) was produced as characterized by 8 M urea-denatured polyacrylamide gel (3.5%) electrophoresis. The purified A-chains of both cinnamomin and ricin showed a slightly different RNA N-glycosidase activity to the domestic silkworm pupal ribosome. It was proposed that the difference of their toxicity to domestic silkworm larvae was not related to their A-chains but to the properties of their B-chains. It was also found that the vomit obtained from the midgut of domestic silkworm larvae could hydrolyze these two proteins apparently to a similar extent.

Detection and characterization of glutathione S-transferase activity in rice EF-1betabeta'gamma and EF-1gamma expressed in Escherichia coli

Plant elongation factor EF-1 consists of four subunits (EF-1alphabetabeta'gamma). EF-1alpha. GTP catalyses the binding of aminoacyl-tRNA to the ribosome. EF-1beta and EF-1beta' catalyze the GDP/GTP exchange on EF-1alpha. GDP. However, the function of EF-1gamma, a subunit detected in eukaryotes, but not in prokaryotes remained unknown. This report demonstrates that rice EF-1betabeta'gamma and recombinant EF-1gamma possess glutathione S-transferase (GST) activity. The EF-1betabeta'gamma- or EF-1gamma-dependent GST activity is about one-fiftieth of the rice GST activity. The Km values of EF-1betabeta'gamma, EF-1gamma, and rice GST for glutathione and 1-chloro-2,4-dinitrobenzene are of about the same order. Although recombinant EF-1gamma is heat labile, active EF-1gamma was obtained by purifying it in the presence of 20% glycerol.

Interactions among four subunits of elongation factor 1 from rice embryo

To establish the subunit construction of elongation factor EF-1, interactions among four non-identical subunits of rice embryo EF-1 (alpha, beta, beta', and gamma) were analyzed with polyacrylamide gel electrophoresis. Complexes beta beta', alpha beta, alpha beta', and beta gamma were formed by mixing the two respective subunits. However, no complex was formed between EF-1 beta' and EF-1 gamma. Complexes containing three subunits like alpha beta beta', alpha beta gamma, and beta beta' gamma, were formed by mixing the three respective subunits. EF-1 was reconstructed when each subunit was added in the following order, beta, beta', gamma, and alpha. The affinity of EF-1 alpha for other subunits was as follows, beta beta' gamma > beta beta' > beta not equal to beta'. Likewise, the affinity of EF-1 gamma for other subunits was: beta beta' gamma > beta >> beta'. Phe-tRNA binding activity of the reconstructed EF-1 was about 90% of that of the native EF-1. From these results, we concluded that rice embryo EF-1 is constructed of equimolar amount of four subunits, alpha, beta, beta' and gamma.

Intracellular messengers and the control of protein synthesis

The molecular events responsible for controlling cell growth and development, as well as their coordinate interaction is only beginning to be revealed. At the basis of these controlling events are hormones, growth factors and mitogens which, through transmembrane signalling trigger an array of cellular responses, initiated by receptor-associated tyrosine kinases, which in turn either directly or indirectly mediate their effects through serine/threonine protein kinases. Utilizing the obligatory response of activation of protein synthesis in cell growth and development, we describe efforts to work backwards along the regulatory pathway to the receptor, identifying those molecular components involved in modulating the rate of translation. We begin by describing the components and steps of protein synthesis and then discuss in detail the regulatory pathways involved in the mitogenic response of eukaryotic cells and during meiotic maturation of oocytes. Finally we discuss possible future work which will further our understanding of these systems.

Effect of cyclic AMP and cyclic GMP on the autophosphorylation of elongation factor 1 from wheat embryos

Extensively purified EF-1H (EF-1 alpha beta beta' gamma) from wheat embryos had a protein kinase activity and phosphorylated EF-1 beta which is one of the two EF-Ts-like factors (EF-1 beta and EF-1 beta'). In this reaction ATP and GTP were equally effective as phosphate donors, and threonine residue was phosphorylated. At 10(-7)M, 3', 5' cyclic GMP stimulated both the phosphorylation and phe-tRNA binding reactions, whereas 3', 5' cyclic AMP inhibited both reactions. These findings indicate that phosphorylation of EF-1H may play an important role in the translational control of protein biosynthesis at the elongation step.

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.

Genes for elongation factor EF-1 alpha in the brine shrimp Artemia

A plasmid carrying a cDNA sequence coding for elongation factor EF-1 alpha from Artemia was used to probe blots of mRNA and chromosomal DNA from Artemia. A messenger length for EF-1 alpha corresponding to 1850 nucleotides was found. Southern blots pointed to a limited number (1-4) of genes, coding for EF-1 alpha. From an Artemia gene library a recombinant phage was isolated, which contains genomic sequences of EF-1 alpha. S1-nuclease mapping indicated the presence of intervening sequences within this cloned gene.

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.

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.

A new purification scheme for elongation factor 1 from rabbit reticulocytes and investigation of the homology of the subunits with those of initiation factor 2

The aim of this work was to compare the subunits of the elongation factor EF-1 and the initiation factor eIF-2 from rabbit reticulocytes. We devised a simple procedure for the purification of EF-1: stepwise chromatography on heparin-Sepharose, separation of the heavy form by sucrose gradient centrifugation, and a final step of stepwise chromatography on RNA-Sepharose. The heparin-Sepharose column also clearly separated EF-1 and EF-2 within one chromatographic step. The EF-1 was 350-fold puried and the yield was 10%. This preparation showed after electrophoresis on polyacylamide gels in the presence of sodium dodecyl sulfate three bands corresponding to those described by others as the subunits, with Mr of 54000, 49000 and 29200. An additional band of Mr 34000 was present but no others. The 49000-Mr and 34000-Mr bands corresponded exactly in molecular weight to two of three subunits of eIF-2. A more detailed comparison was therefore made of all subunits of EF-1 and eIF-2. This was done by examination of chymotryptic fingerprints on polyacrylamide gel electrophoresis. No evidence for homology between EF-1 and eIF-2 was found. However, the two larger subunits of eIF-2 had a majority of chymotryptic fragments in common, thus indicating some homology between these polypeptides.

The isolation and characterization of elongation factor eEF-Ts from Krebs-II mouse-ascites-tumor cells and its role in the elongation process

A factor having activity similar to that described in other systems for the eukaryotic elongation factor eEF-Ts was isolated from the heavy, aggregate form of eEF-TH (formally named EF-1H). This protein has a molecular weight of 52000 under native conditions and of 25500 under denaturing conditions. It has been shown to stimulate eEF-Tu-dependent aminoacyl-tRNA binding to ribosomes and therefore eEF-Tu/eEF-G-dependent polyphenylalanine synthesis by ribosomes and was found to stimulate GDP-GTP exchange in eEF-Tu . GDP complexes. In the course of this work, it was also demonstrated that the removal of deacylated tRNA from the ribosome is a GTP-dependent process. This report, therefore, adds further support to the concept that a third elongation factor, eEF-Ts, may be common to all systems in the eukaryotic domain.