Polypeptide elongation factors of the developing chick brain

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.

Two genes encode related cytoplasmic elongation factors 1 alpha (EF-1 alpha) in Drosophila melanogaster with continuous and stage specific expression

We have characterized two previously cloned genes, F1 and F2 (1) that code for elongation factor EF - 1 alpha of Drosophila melanogaster. Genomic Southern blot hybridization revealed that they are the only gene copies present. We isolated cDNA clones of both transcripts from embryonal and pupal stage of development that cover the entire transcription unit. The 5' ends of both genes have been determined by primer extension and for F1 also by RNA sequencing. These start sites have been shown to be used consistently during development. Comparison of cDNA and genomic sequences revealed that EF - 1 alpha,F1 consists of two and EF - 1 alpha,F2 of five exons. The two described elongation factor genes exhibit several regions of strong sequence conservation when compared to five recently cloned eucaryotic elongation factors.

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. 1. Purification, molecular and immunological properties

This work describes a method for the purification of the elongation factors (EF) from calf brain. The elongation factor responsible for the binding of aminoacyl-tRNA to the ribosome is found in this organ as a light form (EF-1 alpha) and as a component of heavy, polydispersed aggregates (EF-1H). EF-1 beta, the factor enhancing the EF-1 alpha GDP/GTP exchange, is part of EF-1H and of smaller aggregates. The fraction of EF-1 alpha and EF-1 beta not associated with EF-1H, and EF-2 have been purified to homogeneity after several chromatographic steps. EF-1H consists of many proteins; among them, EF-1 alpha, EF-1 beta and an EF-1 gamma-like protein represent three of the major components. This conclusively shows that EF-1H from calf brain is not a polydispersed aggregate of only EF-1 alpha. EF-1 beta has also been purified to homogeneity from EF-1H. The property of EF-1 beta to aggregate with other proteins suggests that this factor plays an important role in the organization of EF-1H. The relative molecular mass of the purified factors have been determined as: EF-1 alpha, 50,000; EF-1 beta, 30,000; the EF-1 gamma-like component, 49,000; EF-2, 85,000. Some cross-reactivity with the antibodies against the prokaryotic counterparts has been shown for EF-1 alpha, EF-1 beta and EF-2 by functional and immuno-precipitation methods, suggesting the existence of structural homologies.