Regulation of protein synthesis factor EF-1 alpha in Mucor racemosus

Methylation of Elongation Factor 1A: Where, Who, and Why?

Eukaryotic elongation factor 1A (eEF1A) is an essential and highly conserved protein involved in diverse cellular processes, including translation, cytoskeleton organisation, nuclear export, and proteasomal degradation. Recently, nine novel and site-specific methyltransferases were discovered that target eEF1A, five in yeast and four in human, making it the eukaryotic protein with the highest number of independent methyltransferases. Some of these methyltransferases show striking evolutionary conservation. Yet, they come from diverse methyltransferase families, indicating they confer competitive advantage through independent origins. As might be expected, the first functional studies of specific methylation sites found them to have distinct effects, notably on eEF1A-related processes of translation and tRNA aminoacylation. Further functional studies of sites will likely reveal other unique roles for this interesting modification.

Saccharomyces cerevisiae Eukaryotic Elongation Factor 1A (eEF1A) Is Methylated at Lys-390 by a METTL21-Like Methyltransferase

The human methyltransferases (MTases) METTL21A and VCP-KMT (METTL21D) were recently shown to methylate single lysine residues in Hsp70 proteins and in VCP, respectively. The yet uncharacterized MTase encoded by the YNL024C gene in Saccharomyces cerevisiae shows high sequence similarity to METTL21A and VCP-KMT, as well as to their uncharacterized paralogues METTL21B and METTL21C. Despite being most similar to METTL21A, the Ynl024c protein does not methylate yeast Hsp70 proteins, which were found to be unmethylated on the relevant lysine residue. Eukaryotic translation elongation factor eEF1A in yeast has been reported to contain four methylated lysine residues (Lys30, Lys79, Lys318 and Lys390), and we here show that the YNL024C gene is required for methylation of eEF1A at Lys390, the only of these methylations for which the responsible MTase has not yet been identified. Lys390 was found in a partially monomethylated state in wild-type yeast cells but was exclusively unmethylated in a ynl024cΔ strain, and over-expression of Ynl024c caused a dramatic increase in Lys390 methylation, with trimethylation becoming the predominant state. Our results demonstrate that Ynl024c is the enzyme responsible for methylation of eEF1A at Lys390, and in accordance with prior naming of similar enzymes, we suggest that Ynl024c is renamed to Efm6 (Elongation factor MTase 6).

The more basic isoform of eEF1A relates to tumour cell phenotype and is modulated by hyper-proliferative/differentiating stimuli in normal lymphocytes and CCRF-CEM T-lymphoblasts

The elongation factor 1A proteins (eEF1A1/A2) are known to play a role in tumours. We previously found that a more basic isoform of eEF1A (MBI-eEF1A) is present in the cytoskeletal/nuclear-enriched extracts of CCRF-CEM T-lymphoblasts but not in those of normal lymphocytes. To obtain deeper knowledge about MBI-eEF1A biology, we investigate from which of the eEF1A proteins, eEF1A1 or eEF1A2, MBI-eEF1A originates and the possibility that its appearance can be modulated by the differentiated or proliferative cell status. CCRF-CEM T-lymphoblasts and normal lymphocytes were cultured with or without differentiation/pro-proliferative stimuli (Phorbol 12-Myristate 13-Acetate (PMA) alone or the combination of phytohaemagglutinin (PHA) with PMA, respectively), and the presence of MBI-eEF1A evaluated together with that of the eEF1A1/A2 mRNAs. Our data indicate that the MBI-eEF1A may derive from eEF1A1 as eEF1A2 is not expressed in CCRF-CEM and normal lymphocytes. Moreover, MBI-eEF1A is inducible in normal lymphocytes upon hyper-proliferative stimuli application; in CCRF-CEM, its presence can be abrogated by PMA-induced differentiation. Finally, MBI-eEF1A may have a functional role in hyper-proliferating/tumour cells as its disappearance reduces the growth of CCRF-CEM and that of PHA/PMA-stimulated lymphocytes. The presented data suggest that MBI-eEF1A may be related to oncogenic cell phenotype, rising the possibility to use MBI-eEF1A as target for novel therapeutic strategies.

Methylation of translation-associated proteins in Saccharomyces cerevisiae: Identification of methylated lysines and their methyltransferases

This study aimed to identify sites of lysine methylation in Saccharomyces cerevisiae and the associated methyltransferases. Hexapeptide ligand affinity chromatography was used to normalize the abundance levels of proteins in whole cell lysate. MS/MS, in association with antibody-based detection, was then used to identify lysine methylated proteins and the precise sites of modification. Lysine methylation was found on the proteins elongation factor (EF) 1-α, 2, and 3A, as well as ribosomal proteins 40S S18-A/B, 60S L11-A/B, L18-A/B, and L42-A/B. Precise sites were mapped in all cases. Single-gene knockouts of known and putative methyltransferase(s), in association with MS/MS, showed that EF1-α is monomethylated by Efm1 at lysin 30 and dimethylated by See1 at lysine 316. Methyltransferase Rkm1 was found to monomethylate 40S ribosomal protein S18-A/B at lysine 48. Knockout analysis also revealed that putative methyltransferase YBR271W affects the methylation of proteins EF2 and 3A; this was detected by Western blotting and immunodetection. This methyltransferase shows strong interspecies conservation and a tryptophan-containing motif associated with its active site. We suggest that enzyme YBR271W is named EF methyltransferase 2 (Efm2), in line with the recent naming of YHL039W as Efm1.

Ethanolamine phosphoglycerol attachment to eEF1A is not essential for normal growth of Trypanosoma brucei

Eukaryotic elongation factor 1A (eEF1A) is the only protein modified by ethanolamine phosphoglycerol (EPG). In mammals and plants, EPG is attached to conserved glutamate residues located in eEF1A domains II and III, whereas in the unicellular eukaryote, Trypanosoma brucei, a single EPG moiety is attached to domain III. A biosynthetic precursor of EPG and structural requirements for EPG attachment to T. brucei eEF1A have been reported, but the role of this unique protein modification in cellular growth and eEF1A function has remained elusive. Here we report, for the first time in a eukaryotic cell, a model system to study potential roles of EPG. By down-regulation of EF1A expression and subsequent complementation of eEF1A function using conditionally expressed exogenous eEF1A (mutant) proteins, we show that eEF1A lacking EPG complements trypanosomes deficient in endogenous eEF1A, demonstrating that EPG attachment is not essential for normal growth of T. brucei in culture.

A cytoplasm-specific activity encoded by the Trithorax-like ATX1 gene

Eukaryotes produce multiple products from a single gene locus by alternative splicing, translation or promoter usage as mechanisms expanding the complexity of their proteome. Trithorax proteins, including the Arabidopsis Trithorax-like protein ATX1, are histone modifiers regulating gene activity. Here, we report that a novel member of the Trithorax family has a role unrelated to chromatin. It is encoded from an internal promoter in the ATX1 locus as an isoform containing only the SET domain (soloSET). It is located exclusively in the cytoplasm and its substrate is the elongation factor 1A (EF1A). Loss of SET, but not of the histone modifying ATX1-SET activity, affects cytoskeletal actin bundling illustrating that the two isoforms have distinct functions in Arabidopsis cells.

Methylation of proteins involved in translation

Methylation is one of the most common protein modifications. Many different prokaryotic and eukaryotic proteins are methylated, including proteins involved in translation, including ribosomal proteins (RPs) and translation factors (TFs). Positions of the methylated residues in six Escherichia coli RPs and two Saccharomyces cerevisiae RPs have been determined. At least two RPs, L3 and L12, are methylated in both organisms. Both prokaryotic and eukaryotic elongation TFs (EF1A) are methylated at lysine residues, while both release factors are methylated at glutamine residues. The enzymes catalysing methylation reactions, protein methyltransferases (MTases), generally use S-adenosylmethionine as the methyl donor to add one to three methyl groups that, in case of arginine, can be asymetrically positioned. The biological significance of RP and TF methylation is poorly understood, and deletions of the MTase genes usually do not cause major phenotypes. Apparently methylation modulates intra- or intermolecular interactions of the target proteins or affects their affinity for RNA, and, thus, influences various cell processes, including transcriptional regulation, RNA processing, ribosome assembly, translation accuracy, protein nuclear trafficking and metabolism, and cellular signalling. Differential methylation of specific RPs and TFs in a number of organisms at different physiological states indicates that this modification may play a regulatory role.

eEF1A isoforms change in abundance and actin-binding activity during maize endosperm development

Eukaryotic elongation factor 1A (eEF1A) appears to be a multifunctional protein because several biochemical activities have been described for this protein, in addition to its role in protein synthesis. In maize (Zea mays) endosperm, the synthesis of eEF1A is increased in o2 (opaque2) mutants, and its concentration is highly correlated with the protein-bound lysine content. To understand the basis of this relationship, we purified eEF1A isoforms from developing endosperm and investigated their accumulation and their functional and structural properties. Formation of three isoforms appears to be developmentally regulated and independent of the o2 mutation, although one isoform predominated in one high lysine o2 inbred. The purified proteins differ in their ability to bind F-actin in vitro, suggesting that they are functionally distinct. However, they share similar aminoacyl-tRNA-binding activities. Tandem mass spectrometry revealed that each isoform is composed of the four same gene products, which are modified posttranslationally by methylation and phosphorylation. The chemical differences that account for their different actin-binding activities could not be determined.

Identification of different isoforms of eEF1A in the nuclear fraction of human T-lymphoblastic cancer cell line specifically binding to aptameric cytotoxic GT oligomers

GT oligomers, showing a dose-dependent cytotoxic effect on a variety of human cancer cell lines, but not on normal human lymphocytes, recognize and form complexes with nuclear proteins. By working with human T-lymphoblastic CCRF-CEM cells and by using MS and SouthWestern blotting, we identified eukaryotic elongation factor 1 alpha (eEF1A) as the main nuclear protein that specifically recognizes these oligonucleotides. Western blotting and supershift assays confirmed the nature of this protein and its involvement in forming a cytotoxicity-related complex (CRC). On the contrary, normal human lymphocytes did not show nuclear proteins able to produce CRC in a SouthWestern blot. Comparative bidimensional PAGE and Western-blotting analysis for eEF1A revealed the presence of a specific cluster of spots, focusing at more basic pH, in nuclear extracts of cancer cells but absent in those of normal lymphocytes. Moreover, a bidimensional PAGE SouthWestern blot demonstrated that cytotoxic GT oligomers selectively recognized the more basic eEF1A isoform expressed only in cancer cells. These results suggest the involvement of eEF1A, associated with the nuclear-enriched fraction, in the growth and maintenance of tumour cells, possibly modulated by post-translational processing of the polypeptide chain.

The eEFIA gene family is differentially expressed in maize endosperm

eEF1A appears to be a multifunctional protein in eukaryotes, where it serves as a protein synthesis factor as well as a cytoskeletal protein. In maize endosperm, the eEF1A concentration is highly correlated with lysine content, and eEF1A synthesis is increased in opaque2 mutants compared to wild type. To investigate the basis for the increased synthesis of eEF1A in opaque2, we characterized the genes encoding this protein and measured their relative level of expression in endosperm and other tissues. Maize contains 10 to 15 eEF1A genes that are nearly identical in nucleotide and amino acid sequences. However, these genes can be distinguished based on their 3' non-coding sequences, which are less conserved. By screening endosperm and seedling cDNA libraries, we show that most of the maize eEF1A genes are expressed, and the relative level of their transcripts varies in different tissues. At least five genes are transcribed in the endosperm, and two account for ca. 80% of the RNA transcripts. The expression of several genes is enhanced in opaque2 endosperm, although the significance of this is unclear.

Phosphoglycerylethanolamine posttranslational modification of plant eukaryotic elongation factor 1alpha

Eukaryotic elongation factor 1alpha (eEF-1A) is a multifunctional protein. There are three known posttranslational modifications of eEF-1A that could potentially affect its function. Except for phosphorylation, the other posttranslational modifications have not been demonstrated in plants. Using matrix-assisted laser desorption/ionization-mass spectrometry and peptide mass mapping, we show that carrot (Daucus carota L.) eEF-1A contains a phosphoglycerylethanolamine (PGE) posttranslational modification. eEF-1A was the only protein labeled with [14C]ethanolamine in carrot cells and was the predominant ethanolamine-labeled protein in Arabidopsis seedlings and tobacco (Nicotiana tabacum L.) cell cultures. In vivo-labeling studies using [3H]glycerol, [32P]Pi, [14C]myristic acid, and [14C]linoleic acid indicated that the entire phospholipid phosphatidylethanolamine is covalently attached to the protein. The PGE lipid modification did not affect the partitioning of eEF-1A in Triton X-114 or its actin-binding activity in in vitro assays. Our in vitro data indicate that this newly characterized posttranslational modification alone does not affect the function of eEF-1A. Therefore, the PGE lipid modification may work in combination with other posttranslational modifications to affect the distribution and the function of eEF-1A within the cell.

Site-directed mutants of post-translationally modified sites of yeast eEF1A using a shuttle vector containing a chromogenic switch

Eukaryotic elongation factor 1A (eEF1A, formerly eEF-1 alpha) carries aminoacyl-tRNAs into the A-site of the ribosome in a GTP-dependent manner. In order to probe the structure/function relationships of eEF1A, we have generated site-directed mutants using a modification of a highly versatile yeast shuttle vector, which consists of the insertion of a 66 base long synthetic DNA fragment in the vector's polylinker. Via oligonucleotide-directed mutagenesis, the modification permits the identification of mutant clones based on a chromogenic screen of beta-galactosidase activity. Mutagenesis reactions are performed with two or more oligonucleotides, one introducing the chromogenic shift, and the other(s) introducing the mutation(s) of interest in eEF1A. Several rounds of chromogenic shifts and additional mutations can be performed in succession on the same vector. To address the possible function of the methylated lysines in yeast eEF1A, we have changed the post-translationally modified lysines (residue 30, 79, 316 and 390) to arginines using the above methodology. Yeast with eEF1A mutants that substitute arginine in all four sites do not show any phenotypic change. There is also an apparent equivalency of wild-type and mutant yeast eEF1A in in vitro assays. It is concluded that the post-translational modifications of eEF1A are not of major importance for eEF1A's role in translation.

Gene expression inMucordimorphism

An ongoing dialectic has concerned the relative importance of differential gene expression versus the pattern of new wall deposition in Mucor dimorphism. Numerous physiological processes and enzyme activities have been observed in flux during morphogenesis, but a causal link to dimorphism has been infrequently demonstrated. Very few of the proteins that are conspicuous in two-dimensional polyacrylamide gel electrophoresis are specific to cell morphology or significantly change in amount during morphogenesis. Cyclic AMP, putrescine, S-adenosylmethionine, and enzymes governing their intracellular concentrations show patterns of change that consistently correlate with morphogenesis. The expression of RAS proteins and translation elongation factor-1α activity during morphogenesis are regulated at the level of transcription and post-translational methylation, respectively. Wall chemistry is very similar in both morphologies, but wall deposition is isodiametric in yeasts and vectorial in hyphae. Electron microscopy shows patterns of apparent exocytosis that are generalized in the former and apical in the latter. Research on other dimorphic fungi, including Saccharomyces cerevisiae, suggests an involvement of cytoskeletal proteins and a family of GTP-linked protein kinases in directing polar growth. Some of these elements, which may be controlled quite distal from the genes encoding them, have been demonstrated in Mucor spp., while others are the subject of ongoing investigations. Key words: Mucor, dimorphism, morphogenesis, gene expression, yeasts, hyphae.

Characterization of yeast EF-1 alpha: non-conservation of post-translational modifications

Elongation factor 1 alpha (EF-1 alpha) is an abundant cellular protein and its amino-acid sequence has been inferred from numerous organisms, including bacteria, archaebacteria, plants and animals. In large measure, it would appear that the overall structure has probably been maintained given the 33% identity and 56% similarity of Escherichia coli EF-Tu with human EF-1 alpha. Chemical sequencing of EF-Tu and EF-1 alpha has revealed that these proteins are post-translationally modified. In order to assess the possible function of these modifications, we have chemically sequenced the EF-1 alpha from the lower eukaryote Saccharomyces cerevisiae (yeast). To our surprise, the methylation pattern of yeast EF-1 alpha was quite different from either rabbit or brine shrimp EF-1 alpha with only the trimethyllysine at position 79 conserved although the yeast protein is 81% identical to rabbit EF-1 alpha. A dimethyllysine was observed at position 316 which corresponds to a trimethyllysine in brine shrimp and rabbit EF-1 alpha. The other positions in yeast EF-1 alpha which were methylated were unrelated to the other six possible positions for modification observed in brine shrimp or rabbit EF-1 alpha. In addition, the unique glyceryl-phosphorylethanolamine observed in mammalian EF-1 alpha and suspected in brine shrimp EF-1 alpha was not found in yeast EF-1 alpha.

Regulation of protein synthesis at the elongation stage. New insights into the control of gene expression in eukaryotes

There are many reports which demonstrate that the rate of protein biosynthesis at the elongation stage is actively regulated in eukaryotic cells. Possible physiological roles for this type of regulation are: the coordination of translation of mRNA with different initiation rate constants; regulation of transition between different physiological states of a cell, such as transition between stages of the cell cycle; and in general, any situation where the maintenance of a particular physiological state is dependent on continuous protein synthesis. A number of covalent modifications of elongation factors offer potential mechanisms for such regulation. Among the various modifications of elongation factors, phosphorylation of eEF-2 by the specific Ca2+calmodulin-dependent eEF-2 kinase is the best studied and perhaps the most important mechanism of regulation of elongation rate. Since this phosphorylation is strictly Ca(2+)-dependent, and makes eEF-2 inactive in translation, this mechanism could explain how changes in the intracellular free Ca2+ concentration may regulate elongation rate. We also discuss some recent findings concerning elongation factors, such as the discovery of developmental stage-specific elongation factors and the regulated binding of eEF-1 alpha to cytoskeletal elements. Together, these observations underline the importance of the elongation stage of translation in the regulation of the cellular processes essential for normal cell life.

Developmental analysis of elongation factor-1 alpha expression in transgenic tobacco

The developmental regulation of the translational elongation factor EF-1 alpha has been analyzed in tobacco. A gene fusion was constructed consisting of the 5' and 3' regions of the tomato genomic clone LeEF-A from the EF-1 alpha gene family and the beta-glucuronidase coding region. Analysis of the transgenic plants containing this chimeric gene demonstrated that the tomato LeEF-A flanking sequences were sufficient to confer expression patterns similar to those of the endogenous tobacco EF-1 alpha gene. The patterns of beta-glucuronidase activity in this system indicated that during plant growth and development EF-1 alpha is regulated with increased expression corresponding to regions of high protein synthesis, including meristems, rapidly growing tissues, and developing gametophytes. In addition, EF-1 alpha expression responds rapidly to changes in growth patterns induced by hormone treatment. Our results are in agreement with studies in animals indicating that EF-1 alpha expression may be rate limiting for protein synthesis and demonstrate that the analysis of EF-1 alpha is of value for studying interrelationships between protein synthesis and developmental control.

Compartmentalization and actin binding properties of ABP-50: the elongation factor-1 alpha of Dictyostelium

ABP-50 is the elongation factor-1 alpha (EF-1 alpha) of Dictyostelium discoideum (Yang et al.: Nature 347:494-496, 1990). ABP-50 is also an actin filament binding and bundling protein (Demma et al.: J. Biol. Chem. 265:2286-2291, 1990). In the present study we have investigated the compartmentalization of ABP-50 in both resting and stimulated cells. Immunofluorescence microscopy shows that in addition to being colocalized with F-actin in surface extensions in unstimulated cells, ABP-50 exhibits a diffuse distribution throughout the cytosol. Upon addition of cAMP, a chemoattractant, ABP-50 becomes localized in the filopodia that are extended as a response to stimulation. Quantification of ABP-50 in Triton-insoluble and -soluble fractions of resting cells indicates that 10% of the total ABP-50 is recovered in the Triton cytoskeleton, while the remainder is in the soluble cytosolic fraction. Stimulation with cAMP increases the incorporation of ABP-50 into the Triton cytoskeleton. The peak of incorporation of ABP-50 at 90 sec is concomitant with filopod extension. Immunoprecipitation of the cytosolic ABP-50 from unstimulated cells using affinity-purified polyclonal anti ABP-50 results in the coprecipitation of non-filamentous actin with ABP-50. Purified ABP-50 binds to G-actin with a Kd of approximately 0.09 microM. The interaction between ABP-50 and G-actin is inhibited by GTP but not by GDP, while the bundling of F-actin by ABP-50 is unaffected by guanine nucleotides. We conclude that a significant amount of ABP-50 is bound to either G- or F-actin in vivo and that the interaction between ABP-50 and F-actin in the cytoskeleton is regulated by chemotactic stimulation.

Functional properties of phosphorylated elongation factor 2

The effect of phosphorylation on the functional activity of eukaryotic elongation factor 2 (eEF-2) was studied using a purified phosphorylated factor. The modified factor was unable to stimulate protein synthesis in an eEF-2-dependent rabbit reticulocyte lysate. The functional alteration was further analyzed by measuring the effects of phosphorylation on the ability of the factor to catalyse the ribosome-dependent hydrolysis of GTP. Kinetic analysis showed that both phosphorylated and unmodified factor was able to hydrolyse GTP with approximately the same maximum rate, indicating that the rate of nucleotide exchange was not impaired by the modification. However, the phosphorylated factor showed a marked reduction in the second-order rate constant, suggesting that the phosphorylation interfered with ribosome.eEF-2 complex formation by reducing the affinity of eEF-2 for the ribosome. This assumption was confirmed by direct measurements of the dissociation constants for the ribosomal complexes containing unmodified and phosphorylated eEF-2.

Role of lysine methylation in the activities of elongation factor 1 alpha

Previous work in our laboratory has demonstrated that 19% of the lysine residues in the protein synthesis elongation factor (EF-1 alpha) are methylated when the factor is purified from the mycelial form of the fungus Mucor racemosus. However, the same factor, when purified from spores of M. racemosus, is largely unmethylated. Despite its wide-spread occurrence in a great number of basic proteins, the functional significance of lysine N-methylation remains poorly understood. Spore and mycelial forms of EF-1 alpha were therefore compared in a series of assays to determine their relative affinities for various substrates and cofactors known to interact with the factor during the elongation cycle. The results suggested that hypomethylated and fully methylated EF-1 alpha had equal affinities for GTP, aminoacyl-tRNA, and ribosomes. Also, methylation did not appear to affect the accuracy of translation in an in vitro system. However, experiments did suggest that methylation may affect the ability of the factor to form complexes with other subunits (EF-1 beta gamma) which are known to enhance the overall rate of protein synthesis.

Heat shock-related decline in activity and amounts of active elongation factor 1 alpha in ageing and immortal human cells

A significant decline in amount of active elongation factor, EF-1 alpha, and in its catalytic activity was observed in cell-free extracts prepared from normal human diploid fibroblasts (MRC-5) and their SV40-transformed counterparts, after subjecting the cells to 60 min heat shock at different temperatures. Old MRC-5 cells which had become senescent on serial passaging were more sensitive to heat shock-related changes in activity and amounts of active EF-1 alpha than were rapidly proliferating normal and transformed cells.

Effect of acclimation temperature on the elongation step of protein synthesis in different organs of rainbow trout

Cytosolic extracts of liver, kidney, spleen, gill, red and white muscle from rainbow trout acclimated to 4 and 17 degrees C, respectively, have been investigated in vitro with respect to their enzymic activity in stimulating the growth of nascent peptide chains (labelled polyphenylalanine) at assay temperatures from 5 to 25 degrees C using polyuracil as messenger RNA. The elongation step of protein synthesis is characterized by a Q10 value of about 2.4 (range 10-25 degrees C) in all organs from both, 4 and 17 degrees C acclimated fish. Except for the red muscle, the organs of cold acclimated trout, however, exhibit significantly higher specific elongation rates (mol phenylalanine polymerized/(g wet weight X h)) at any experimental temperature than those of warm acclimated fish. This increase of the elongation rates varies between the organs and ranges from +29% (liver) to +60% in the gill. The specific acylation rate (mol phenylalanyl-tRNA formed/(g wet weight X h] surpasses the specific elongation rate by a factor of at least 8.5. Moreover, the specific acylation rate per mg protein is independent of acclimation temperature. It is concluded that the increased specific elongation rates in 4 degrees C acclimated trout are not due to altered pool sizes of the precursor phenylalanyl-tRNA, but reflect an effective enhancement of enzymic elongation factor activities. In accordance with data taken from literature, this finding suggests a compensatory enhancement of in vivo protein synthesis to occur in trout during cold acclimation.

Changes in activity and amount of active elongation factor 1 alpha in aging and immortal human fibroblast cultures

Stoichiometrically estimated amounts of active elongation factor, EF-1 alpha, remain constant in serially passaged Phase II cultures of human fibroblasts, MRC-5, but decrease by 45% towards the end (Phase III) of their lifespan. Catalytic activity of EF-1 alpha is also reduced by 35% in Phase III old cells. The SV40 transformed immortal cell line MRC-5V2 has 30% higher levels of active EF-1 alpha without significant increase in its catalytic activity. Low-serum-associated G1 arrest of normal and transformed cells reduces amounts of active EF-1 alpha by 35% and 20%, respectively. Catalytic activity, however, is reduced rapidly only in G1 arrested normal cells and not in transformed cells. Even though the cell cycle-related changes are reversible both in normal and transformed cells, the age-related decline in amounts of active EF-1 alpha and its activity are irreversible and, most probably, crucial.

In vitro methylation of the elongation factor EF-Tu from Escherichia coli

The in vitro methylation of the elongation factor EF-Tu from Escherichia coli was investigated. The methylation of newly synthesized EF-Tu was obtained using lambda rifd 18 DNA as template and S-adenosyl [methyl-3H]methionine as methyl donor. About 3 mol methyl residues were incorporated for every 10 mol EF-Tu synthesized. Analysis of the nature of the methyl-containing residues by protein hydrolysis followed by paper chromatography showed that both mono- and dimethyllysine were present. The methylation of EF-Tu was also studied separately from its synthesis by using cell-free systems with artificially undermethylated components.