A novel variant of translation elongation factor-1beta: isolation and characterization of the rice gene encoding EF-1beta2

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.

Mutation of a conserved CDK site converts a metazoan Elongation Factor 1Bbeta subunit into a replacement for yeast eEF1Balpha

Elongation factor subunit eEF1Bbeta (formerly EF-1beta in plants and EF-1delta in animals) was identified and cloned in a screen for proteins from pea that interact with a cyclin-dependent kinase (CDK). CDKs are enzymes that regulate progression through meiotic and mitotic cell cycles in eukaryotes. eEF1Bbeta and the related protein eEF1Balpha (formerly EF-1beta' in plants and EF-1beta in animals and fungi) can catalyze GTP/GDP exchange on the G-protein eEF1A (formerly EF-1alpha in plants, animals and fungi) during the elongation phase of protein synthesis in eukaryotes. Recombinant Cdc2 and its native homologues from pea extracts associated both in vitro and in vivo with eEF1Bbeta. A Cdc2-cyclin B complex phosphorylated recombinant plant eEF1Bbetas, but not eEF1Balpha. These interactions between CDK and eEF1Bbeta prompted investigations into the in vivo consequences of this relationship. Expression of cDNAs encoding rice or pea eEF1Bbeta subunits failed to complement a Saccharomyces cerevisiae mutant deleted for the eEF1Balpha gene, as was previously observed for the human eEF1Bbeta. However, replacement of Thr91, the sole consensus CDK phosphorylation site in pea eEF1Bbeta, with alanine allowed the pea protein to substitute for eEF1Balpha function in vivo. In addition, this rescued strain was severely cold sensitive, and more sensitive to translational inhibitors than wild-type yeast. Taken together, these results suggest a physiological connection between the cyclin-dependent class of kinases and a translational elongation factor in mitotic cells, and provide the first in vivo evidence that an altered form of eEF1Bbeta can serve as the guanine nucleotide exchange factor for eEF1A.

Structure and characterization of the gene encoding alpha subunit of soybean beta-conglycinin

beta-conglycinin, a soybean seed storage protein, is comprised of three different subunits, a, alpha', and beta. Several candidates for the alpha subunit gene have been isolated, however, the structure of the alpha subunit gene has not been completely determined. Accordingly, it was also unknown which of the gene candidates are functionally active. Here, we have determined the nucleotide sequence and transcription start site of the alpha subunit gene, and compared the structural components with those of the other subunits or other seed protein genes. The a subunit gene, which is located on a 7.6-kb EcoRI fragment, was composed of six exons that had the same organization as those for the alpha' subunit gene. Within a 400 bp upstream region of the transcription start site, four regions (designated as boxes I, II, III, and IV) were found to be conserved among the alpha, alpha', and other seed protein genes. Genomic Southern blot analysis of soybean varieties lacking the alpha subunit gene candidate indicated that the gene characterized in this paper actually encodes the a subunit and is functionally active. In addition, these experiments revealed the presence of an additional gene which is also responsible for the expression of the a subunit.

Molecular cloning and characterization of the Arabidopsis thaliana alpha-subunit of elongation factor 1B

Using a PCR-based approach, we have isolated two Arabidopsis thaliana cDNA clones (alpha1 and alpha2) encoding the alpha-subunit of translation elongation factor 1B (eEF1Balpha). They encode open reading frames of 228 and 224 amino acids respectively, with extensive homology to eEF1Balpha subunits from different organisms, particularly in the C-terminal half of the protein. They both lack a conserved phosphorylation site that has been implicated in regulating nucleotide exchange activity. Using a plasmid shuffling experiment, we demonstrated that both alpha1 and alpha2 clones are able to complement a mutant yeast strain deficient for the eEF1Balpha subunit. This provides evidence that Arabidopsis encodes at least two functional isoforms of this subunit, termed eEF1Balpha1 and eEF1Balpha2. A third cDNA clone was isolated that appeared to result from an alternative splicing event of the eEF1Balpha1 gene.