Molecular cloning of Xenopus elongation factor 1 gamma, major M-phase promoting factor substrate

Drosophila translational elongation factor-1gamma is modified in response to DOA kinase activity and is essential for cellular viability

Drosophila translational elongation factor-1gamma (EF1gamma) interacts in the yeast two-hybrid system with DOA, the LAMMER protein kinase of Drosophila. Analysis of mutant EF1gamma alleles reveals that the locus encodes a structurally conserved protein essential for both organismal and cellular survival. Although no genetic interactions were detected in combinations with mutations in EF1alpha, an EF1gamma allele enhanced mutant phenotypes of Doa alleles. A predicted LAMMER kinase phosphorylation site conserved near the C terminus of all EF1gamma orthologs is a phosphorylation site in vitro for both Drosophila DOA and tobacco PK12 LAMMER kinases. EF1gamma protein derived from Doa mutant flies migrates with altered mobility on SDS gels, consistent with it being an in vivo substrate of DOA kinase. However, the aberrant mobility appears to be due to a secondary protein modification, since the mobility of EF1gamma protein obtained from wild-type Drosophila is unaltered following treatment with several nonspecific phosphatases. Expression of a construct expressing a serine-to-alanine substitution in the LAMMER kinase phosphorylation site into the fly germline rescued null EF1gamma alleles but at reduced efficiency compared to a wild-type construct. Our data suggest that EF1gamma functions in vital cellular processes in addition to translational elongation and is a LAMMER kinase substrate in vivo.

Phosphorylation of threonine 204 of DEAD-box RNA helicase DDX3 by cyclin B/cdc2 in vitro

DDX3 is a DEAD-box RNA helicase involved in human immunodeficiency virus mRNA export and translation. Previously, we reported that DDX3 is required for cyclin A expression. To examine whether DDX3 is regulated at the post-transcriptional level, we determined the phosphorylation sites of hamster DDX3 in vitro. Threonine 204 (Thr204) is a conserved amino acid residue of DDX3 homologues in yeast, frog, hamster, and human that is located within motif Q of DEAD-box RNA helicases. A Thr204 to Glu204 DDX3 mutant protein lost its function, suggesting that phosphorylation at Thr204 affects DDX3 function. Thr204 was phosphorylated by cyclin B/cdc2. Thr323 in motif Ib was also phosphorylated by cyclin B/cdc2 kinase. We propose a novel function of cyclin B/cdc2 kinase in mitosis, which is to cause a loss of DDX3 function to repress cyclin A expression and to decrease ribosome biogenesis and translation during mitosis.

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.

Mitotic regulation of ribosomal S6 kinase 1 involves Ser/Thr, Pro phosphorylation of consensus and non-consensus sites by Cdc2

During mitosis, the cyclin-dependent kinase, Cdc2, signals the inactivation of major anabolic processes such as transcription, mRNA processing, translation, and ribosome biogenesis, thereby providing energy needed for the radical and energetically costly structural reorganization of the cell. This is accomplished by phosphorylation and inactivation of several key anabolic elements, including TFIIIB, TFIID, RNA polymerase II, poly(A) polymerase, and translation elongation factor 1gamma. We report here that ribosomal S6 kinase 1 (S6K1), a protein kinase linked to the translation of ribosomal protein mRNAs, is also subject to regulation by Cdc2 in mitosis. In mitotic HeLa cells, when the activity of Cdc2 is high, S6K1 is phosphorylated at multiple Ser/Thr, Pro (S/TP) sites, including Ser(371), Ser(411), Thr(421), and Ser(424). Concomitant with this, the phosphorylation of the hydrophobic motif site, Thr(389), is reduced resulting in a decrease in the specific activity of S6K1. The mitotic S/TP phosphorylation sites are readily phosphorylated by Cdc2.cyclin B in vitro. These proline-directed phosphorylations are sensitive to chemical inhibitors of Cdc2 but not to inhibitors of mammalian target of rapamycin, phosphatidylinositol 3-kinase, MEK1/2, or p38. In murine FT210 cells arrested in mitosis, conditional inactivation of Cdc2 reduces phosphorylation of S6K1 at S/TP sites while simultaneously increasing phosphorylation of Thr(389) and of the S6K1 substrate, RPS6. A physical interaction exists between Cdc2 and S6K1, and this interaction is enhanced in mitotic cells. These results suggest that Cdc2 provides a signal that triggers inactivation of S6K1 in mitosis, presumably serving to spare energy for costly mitotic processes at the expense of ribosomal protein synthesis.

Screening for sequence-specific RNA-BPs by comprehensive UV crosslinking

BACKGROUND

Specific cis-elements and the associated trans-acting factors have been implicated in the post-transcriptional regulation of gene expression. In the era of genome wide analyses identifying novel trans-acting factors and cis-regulatory elements is a step towards understanding coordinated gene expression. UV-crosslink analysis is a standard method used to identify RNA-binding proteins. Uridine is traditionally used to radiolabel substrate RNAs, however, proteins binding to cis-elements particularly uridine poor will be weakly or not detected. We evaluate here the possibility of using UV-crosslinking with RNA substrates radiolabeled with each of the four ribonucleotides as an approach for screening for novel sequence specific RNA-binding proteins.

RESULTS

The radiolabeled RNA substrates were derived from the 3'UTRs of the cloned Eg and c-mos Xenopus laevis maternal mRNAs. Specific, but not identical, uv-crosslinking signals were obtained, some of which corresponded to already identified proteins. A signal for a novel 90 kDa protein was observed with the c-mos 3'UTR radiolabeled with both CTP and GTP but not with UTP. The binding site of the 90 kDa RNA-binding protein was localised to a 59-nucleotide portion of the c-mos 3'UTR.

CONCLUSION

That the 90 kDa signal was detected with RNAs radiolabeled with CTP or GTP but not UTP illustrates the advantage of radiolabeling all four nucleotides in a UV-crosslink based screen. This method can be used for both long and short RNAs and does not require knowledge of the cis-acting sequence. It should be amenable to high throughput screening for RNA binding proteins.

Isolation and characterization of Leishmania infantum cDNA encoding a protein homologous to eukaryotic elongation factor 1 gamma

This paper reports the isolation and characterization of a complementary deoxyribonucleic acid clone showing sequence homology with genes coding for the eukaryotic elongation factor 1 gamma (EF-1 gamma). The clone encodes an open reading frame of 404 amino acids corresponding to a deduced molecular mass of 46.2 kDa. Database searches revealed 30-64% sequence identity between the Leishmania infantum EF-1 gamma and several eukaryotic homologues. Southern blot analysis indicated that 2 genes tandemly organized were present in the L. infantum genome. The 3' untranslated regions of these 2 genes differed in size. Southern hybridization and pulsed field gel electrophoresis showed that EF-1 gamma genes are highly conserved among members of the Leishmania genus and must be clustered in a single chromosomal locus.

A large-scale insertional mutagenesis screen in zebrafish

It is estimated that approximately 2500 genes are essential for the normal development of a zebrafish embryo. A mutation in any one of these genes can result in a visible developmental defect, usually followed by the death of the embryo or larva by days 5-7 of age. We are performing a large-scale insertional mutagenesis screen in the zebrafish with the goal of isolating approximately 1000 embryonic mutations. We plan to clone a significant fraction of the mutated genes, as these are the genes important for normal embryogenesis of a vertebrate. To achieve this goal, we prepared approximately 36, 000 founder fish by injecting blastula-stage embryos with one of two pseudotyped retroviruses. We estimate that together these fish harbor between 500,000-1,000,000 proviral insertions in their germ lines. The protocol we have devised and the size of our facility allow us to breed approximately 80,000-150,000 of these insertions to homozygosity within 2 years. Because a pilot screen conducted earlier in our laboratory revealed that the frequency of mutations obtained with this type of insertional mutagen is 1 embryonic lethal mutation per 70-100 proviral insertions, screening 100,000 insertions should yield at least 1000 mutants. Here we describe the protocol for the screen and initial results with the first of the two retroviral vectors used, a virus designated F(5). We screened an estimated 760 insertions among F(3) progeny from 92 F(2) families and obtained 9 recessive embryonic lethal mutations. Thus, the efficiency of mutagenesis with this viral vector is approximately one-ninth that observed with the chemical mutagen ENU in zebrafish. We have also obtained two dominant mutations, one of which is described here. As expected, mutated genes can be readily identified. So far, genes mutated in four of the nine recessive mutants and one of the two dominant mutants have been cloned. Further improvements to this technology could make large-scale insertional mutagenesis screening and rapid gene cloning accessible to relatively small zebrafish laboratories.

Isolation and characterization of a rice cDNA encoding the gamma-subunit of translation elongation factor 1B (eEF1Bgamma)

We isolated a rice cDNA clone (refg) encoding the gamma-subunit of translation elongation factor 1B (eEF-1B gamma; the old designation was EF-1 gamma). The refg encodes an open reading frame of 419 amino acids which shows a similarity to the equivalent sequences from animals and yeast. Complex formation analysis, which showed the recombinant protein of refg (His-eEF1B gamma) and formed a complex with GST-eEF-1Bbeta, indicated that the refg encodes rice eEF1B gamma of the eEF1B alphabeta gamma complex. Expression analysis showed that refg mRNA is very abundant in suspension-cultured cells during the exponential phase of growth. A DNA blot analysis indicated that refg is located at a single locus in the rice genome.

Phosphorylation of elongation factor-1 (EF-1) by cdc2 kinase

Elongation factor-1 (EF-1) is a major substrate for cdc2 kinase in Xenopus oocytes. The guanine-nucleotide exchange factor EF-1 beta gamma delta, appears to have a highly complex macromolecular structure containing several GTP/GDP exchange proteins, valyl-tRNA synthetase, and a putative anchoring protein EF-1 gamma. During meiotic cell division, the factor becomes phosphorylated by cdc2 kinase, not only on EF-1 gamma, but also on two different phospho-acceptors on EF-1 delta. Phosphorylation is concomitant with changes in protein synthesis in vivo. Xenopus oocytes, and potentially all cells, contain a multitude of heteromeric forms of the complex which postulates that EF-1 beta gamma delta is not a "house keeping" factor but a sophisticated regulatory element.

Recombinant subunits of mammalian elongation factor 1 expressed in Escherichia coli. Subunit interactions, elongation activity, and phosphorylation by protein kinase CKII

The first step in elongation requires two different activities; elongation factor (EF)-1alpha transfers aminoacyl-tRNA to the ribosome and is released upon hydrolysis of GTP, EF-1betagammadelta catalyzes exchange of GDP on EF-1alpha with GTP. To analyze the role of the individual subunits of EF-1 in elongation, the cDNAs for the beta, gamma, and delta subunits of EF-1 from rabbit were cloned, and proteins of 225, 437, and 280 amino acids, respectively, were expressed in Escherichia coli. The purified recombinant beta subunit migrates as a dimer and the gamma subunit as a trimer upon gel filtration, whereas the delta subunit forms a large aggregate. Complexes of betagamma, gammadelta and betagammadelta were formed by self-association and eluted with a molecular mass of approximately 160, 530, and 670 kDa, respectively; no interaction was observed between beta and delta. The activity of the recombinant subunits was determined with native EF-1alpha by measuring stimulation of the rate of elongation by poly(U)-directed polyphenylalanine synthesis. Recombinant beta and delta alone stimulated the rate of elongation by 10-fold, with a ratio of 5alpha:2beta or delta. The betagammadelta complex stimulated EF-1alpha activity up to 10-fold with a ratio of 20alpha to 1betagammadelta. Phosphorylation of the beta and delta subunits alone or in betagammadelta by protein kinase CKII had no effect on the rate of elongation.

XMAP310: a Xenopus rescue-promoting factor localized to the mitotic spindle

To understand the role of microtubule-associated proteins (MAPs) in the regulation of microtubule (MT) dynamics we have characterized MAPs prepared from Xenopus laevis eggs (Andersen, S.S.L., B. Buendia, J.E. Domínguez, A. Sawyer, and E. Karsenti. 1994. J. Cell Biol. 127:1289-1299). Here we report on the purification and characterization of a 310-kD MAP (XMAP310) that localizes to the nucleus in interphase and to mitotic spindle MTs in mitosis. XMAP310 is present in eggs, oocytes, a Xenopus tissue culture cell line, testis, and brain. We have purified XMAP310 to homogeneity from egg extracts. The purified protein cross-links pure MTs. Analysis of the effect of this protein on MT dynamics by time-lapse video microscopy has shown that it increases the rescue frequency 5-10-fold and decreases the shrinkage rate twofold. It has no effect on the growth rate or the catastrophe frequency. Microsequencing data suggest that XMAP230 and XMAP310 are novel MAPs. Although the three Xenopus MAPs characterized so far, XMAP215 (Vasquez, R.J., D.L. Gard, and L. Cassimeris. 1994. J. Cell Biol. 127:985-993), XMAP230, and XMAP310 are localized to the mitotic spindle, they have distinct effects on MT dynamics. While XMAP215 promotes rapid MT growth, XMAP230 decreases the catastrophe frequency and XMAP310 increases the rescue frequency. This may have important implications for the regulation of MT dynamics during spindle morphogenesis and chromosome segregation.

Genomic structure and sequence analysis of the valyl-tRNA synthetase gene of the Japanese pufferfish, Fugu rubripes

The genomic sequence and exon-intron organisation of the valyl-tRNA synthetase gene in the Japanese pufferfish, Fugu rubripes, have been determined. This single-copy Fugu gene spans 8.5 kb, about 2.5 times smaller than that in man (21 kb). It contains 29 exons, with the largest intron being 1008 bp. The predicted polypeptide consists of 1217 amino acids, with a molecular weight of 138 kD and an isoelectric point of 7.27. It shares 40% identity in the overlapping region with its homolog in bacteria, 47% with yeast, and 67% with man. The Fugu gene has an additional N-terminal sequence which shows strong similarity to elongation factory-1gamma, a feature it shares only with the human sequence, but not with any other lower eukaryote or prokaryote studied so far. This N-terminal segment is encoded in the first six exons, suggesting their capture by a translocation through introns. Indeed, the acquisition of extra domains to perform related functions in RNA splicing and translation of polypeptides has already been observed in other aminoacyl-tRNA synthetases. Two cDNA sequences of human valyl-tRNA synthetase have been published, with discrepancies between them. Aided by comparisons with the Fugu gene, three of these discrepancies have been resolved, involving the elucidation of the sequence and positions of two introns. This compact vertebrate genome has demonstrated its value as a tool for the analysis of genes at the genomic level.

Expression of recombinant elongation factor 1 beta from rabbit in Escherichia coli. Phosphorylation by casein kinase II

The beta subunit of eukaryotic elongation factor 1 (EF-1) catalyzes the GDP/GTP exchange activity on EF-1 alpha. In these studies, two cDNAs for the beta subunit of EF-1 from rabbit are cloned and sequenced. The cDNAs consist of 808 and 798 bp and are identical except for the 5' leader sequences of 67 and 57 bp. Both cDNAs code for a protein of 225 amino acids. Using the pT7-7 expression vector, EF-1 beta was expressed in Escherichia coli and purified to apparent homogeneity by chromatography on DEAE-cellulose and FPLC on Superose 12 and Mono Q. EF-1 beta was highly phosphorylated by casein kinase II, with up to 1.3 mol of phosphate incorporated per mol protein. From microsequence analysis and manual Edman degradation, the majority of the phosphate was shown to be present in serine 106 in the peptide DLFGS106DDEEES112EEA. Serine 112 was also phosphorylated by casein kinase II, but to a lesser extent. Previously, little phosphorylation of the beta subunit by casein kinase II was observed in native EF-1 unless GDP was bound to the alpha subunit (Palen, E., Venema, R.C., Chang, Y-W.E. and Traugh, J.A. (1994) Biochemistry, 8515-8520). In contrast, purified recombinant EF-1 beta was highly and specifically phosphorylated by casein kinase II; GDP and polylysine had little effect on the rate of phosphorylation of the purified subunit.

The overexpression of elongation factor 1 gamma mRNA in gastric carcinoma

BACKGROUND

Elongation factor 1 gamma (EF1 gamma) has been isolated from a pancreatic cancer cell line, while the overexpression of EF1 gamma has also been observed in colorectal carcinomas and adenomas. There is, however, still little information on the expression of EF1 gamma in gastric carcinoma.

METHODS

The authors examined the expression of EF1 gamma mRNA in 30 gastric carcinomas and their corresponding paired adjacent normal mucosae obtained during surgery while also examining 10 human digestive tract carcinoma cell lines using Northern blot hybridization.

RESULTS

An overexpression was observed in 22 (73%) of 30 gastric carcinomas, relative to the corresponding normal tissue. In a clinicopathologic study, no relationship was observed between the overexpression of EF1 gamma mRNA and the histologic grading or depth of tumor invasion. However, 15 (68%) of 22 overexpressed cases were positive for vascular permeation, whereas only 1 of 8 nonoverexpressed cases was positive for vascular permeation, and the difference was significant (P < 0.05). Nine (90%) of 10 with more than a 10-fold overexpression relative to the corresponding normal tissue showed severe vascular permeation in the histologic specimens. Conversely, the expression of EF1 gamma was observed not only in the pancreatic and gastric carcinoma cell lines, but also in the hepatic, ileocecal, duodenal, and colon carcinoma cell lines.

CONCLUSIONS

The overexpression of EF1 gamma mRNA was observed in both the gastric carcinoma tissue and in all the other cell lines examined. This probable correlation with vascular permeation in gastric carcinoma is thus considered to provide another piece of useful pathologic information.

The leucine-zipper in elongation factor EF-1 delta, a guanine-nucleotide exchange protein, is conserved in Artemia and Xenopus

Elongation factor 1, a complex involved in protein biosynthesis, contains two guanine-nucleotide-exchange proteins EF-1 beta and EF-1 delta. The sequence of EF-1 delta of Artemia was determined with the purified protein. When compared to EF-1 delta from Xenopus, a high degree of identify (80%) was found in the C-terminal domains of the proteins, which contain the guanine-nucleotide-exchange activity. The N-terminal domains share only 23% of the amino acids at identical positions, and therefore they were further analysed for less obvious types of homology. To this end, a published approach for sequence analysis, which can detect peculiar amino acid patterns in proteins was applied. In this way, a weak albeit unmistakable similarity between the two EF-1 delta proteins was demonstrated in the region of the leucine-zippers, apart from the leucine repeat itself. Apparently, they display a common structural pattern in their N-terminal domains, which so far has been observed mainly in transcription factors.

Multiple genes encode the translation elongation factor EF-1 gamma in Saccharomyces cerevisiae

A gene encoding a yeast homologue of translation elongation factor 1 gamma (EF-1 gamma), TEF3, was isolated as a gene dosage extragenic suppressor of the cold-sensitive phenotype of the Saccharomyces cerevisiae drs2 mutant. The drs2 mutant is deficient in the assembly of 40S ribosomal subunits. We have identified a second gene, TEF4, that encodes a protein highly related to both the Tef3p protein (Tef3p), and EF-1 gamma isolated from other organisms. In contrast to TEF3, the TEF4 gene contains an intron. Gene disruptions showed that neither gene is required for mitotic growth. Haploid spores containing disruptions of both genes are viable and have no defects in ribosomal subunit composition or polyribosomes. Unlike TEF3, extra copies of TEF4 do not suppress the cold-sensitive 40S ribosomal subunit deficiency of a drs2 strain. Low-stringency genomic Southern hybridization analysis indicates there may be additional yeast genes related to TEF3 and TEF4.

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.

DRS1 to DRS7, novel genes required for ribosome assembly and function in Saccharomyces cerevisiae

To identify Saccharomyces cerevisiae mutants defective in assembly or function of ribosomes, a collection of cold-sensitive strains generated by treatment with ethyl methanesulfonate was screened by sucrose gradient analysis for altered ratios of free 40S to 60S ribosomal subunits or qualitative changes in polyribosome profiles. Mutations defining seven complementation groups deficient in ribosomal subunits, drs1 to drs7, were identified. We have previously shown that DRS1 encodes a putative ATP-dependent RNA helicase necessary for assembly of 60S ribosomal subunits (T. L. Ripmaster, G. P. Vaughn, and J. L. Woolford, Jr., Proc. Natl. Acad. Sci. USA 89:11131-11135, 1992). Strains bearing the drs2 mutation process the 20S precursor of the mature 18S rRNA slowly and are deficient in 40S ribosomal subunits. Cloning and sequencing of the DRS2 gene revealed that it encodes a protein similar to membrane-spanning Ca2+ ATPases. The predicted amino acid sequence encoded by DRS2 contains seven transmembrane domains, a phosphate-binding loop found in ATP- or GTP-binding proteins, and a seven-amino-acid sequence detected in all classes of P-type ATPases. The cold-sensitive phenotype of drs2 is suppressed by extra copies of the TEF3 gene, which encodes a yeast homolog of eukaryotic translation elongation factor EF-1 gamma. Identification of gene products affecting ribosome assembly and function among the DNAs complementing the drs mutations validates the feasibility of this approach.

DRS1 to DRS7, novel genes required for ribosome assembly and function in Saccharomyces cerevisiae

To identify Saccharomyces cerevisiae mutants defective in assembly or function of ribosomes, a collection of cold-sensitive strains generated by treatment with ethyl methanesulfonate was screened by sucrose gradient analysis for altered ratios of free 40S to 60S ribosomal subunits or qualitative changes in polyribosome profiles. Mutations defining seven complementation groups deficient in ribosomal subunits, drs1 to drs7, were identified. We have previously shown that DRS1 encodes a putative ATP-dependent RNA helicase necessary for assembly of 60S ribosomal subunits (T. L. Ripmaster, G. P. Vaughn, and J. L. Woolford, Jr., Proc. Natl. Acad. Sci. USA 89:11131-11135, 1992). Strains bearing the drs2 mutation process the 20S precursor of the mature 18S rRNA slowly and are deficient in 40S ribosomal subunits. Cloning and sequencing of the DRS2 gene revealed that it encodes a protein similar to membrane-spanning Ca2+ ATPases. The predicted amino acid sequence encoded by DRS2 contains seven transmembrane domains, a phosphate-binding loop found in ATP- or GTP-binding proteins, and a seven-amino-acid sequence detected in all classes of P-type ATPases. The cold-sensitive phenotype of drs2 is suppressed by extra copies of the TEF3 gene, which encodes a yeast homolog of eukaryotic translation elongation factor EF-1 gamma. Identification of gene products affecting ribosome assembly and function among the DNAs complementing the drs mutations validates the feasibility of this approach.

Sequence of a fission yeast gene encoding a protein with extensive homology to eukaryotic elongation factor-1 gamma

A polypeptide with an apparent molecular mass of 23 kDa was identified, that exhibited an affinity to a 491-bp DNA derived from one of the Schizosaccharomyces pombe centromeric DNAs (cen1). After determining its N-terminal amino acid (aa) sequence, a Sz. pombe genomic DNA encompassing the coding sequence of the isolated protein was cloned, and a 2.3-kb genomic DNA region sequenced. Further sequence analysis of cDNA clones, originating from this particular genomic region, confirmed the existence of an open reading frame with a short intron, which encodes a 409-aa protein with striking homology to eukaryotic elongation factor-1 gamma.

Expression of elongation factor 1 alpha (EF-1 alpha) and 1 beta gamma (EF-1 beta gamma) are uncoupled in early Xenopus embryos

In the amphibian Xenopus laevis, the elongation factor 1 alpha proteins (EF-1 alpha) synthesised in oocytes and somatic cells correspond to distinct gene products. Furthermore, the somatic EF-1 alpha gene (EF-1 alpha S) produces one of the most highly expressed early zygotic transcripts in the embryo. The functional recycling of EF-1 alpha (conversion of EF-1 alpha-GDP to EF-1 alpha-GTP) is assured by the EF-1 beta gamma complex. We show here that in Xenopus laevis embryos, contrary to the situation for EF-1 alpha, EF-1 beta, and EF-1 gamma mRNAs are transcribed from the same genes in oocytes and somatic cells. In addition, the onset of transcription of the EF-1 beta and EF-1 gamma genes from the zygotic genome occurs several hours after that of the somatic EF-1 alpha S gene. Therefore, during early Xenopus development the expression of these three elongation factors is not co-ordinated at the transcriptional level. The consequences of this uncoupling on the efficiency of translational elongation in the early Xenopus embryo are discussed.

Elongation factor-1 messenger-RNA levels in cultured cells are high compared to tissue and are not drastically affected further by oncogenic transformation

Copy-DNA clones covering the complete coding sequence of human Elongation Factor-1 gamma mRNA have been isolated and characterized. The expression of Elongation Factor-1 in a variety of cell lines and a number of tissues shows a large increase in Elongation Factor-1 mRNA going from tissue to cultured cells (20-fold). Messenger-RNA levels for Elongation Factor-1 alpha, -1 beta and -1 gamma increase in parallel suggesting coordinate regulation of the expression of these genes. Oncogenic transformation in vitro does not strongly affect Elongation Factor-1 mRNA levels.

Phosphorylation of Xenopus elongation factor-1 gamma by cdc2 protein kinase: identification of the phosphorylation site

The cdc2 protein kinase phosphorylates elongation factor-1 gamma (EF-1 gamma) during meiotic maturation of Xenopus oocytes. A synthetic peptide P2: PKKETPKKEKPA matching the cDNA-deduced sequence of EF-1 gamma was an in vitro substrate for cdc2 protein kinase and inhibited phosphorylation of EF-1 gamma. Tryptic hydrolysis of EF-1 gamma and the P2 peptide, both phosphorylated by cdc2 protein kinase, resulted in multiple partial digestion products generated by the presence of barely hydrolysable bonds. The two peptides obtained from the hydrolysis of EF-1 gamma comigrated exactly in two-dimensional separation with two of the P2 peptide hydrolysates. EF-1 gamma therefore contains one unique phosphoacceptor for cdc2 protein kinase, identified as threonine-230.

Human cDNAs encoding elongation factor 1 gamma and the ribosomal protein L19

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