No abstract

p43 is one of the three auxiliary components invariably associated with nine aminoacyl-tRNA synthetases as a multienzyme complex ubiquitous to all eukaryotic cells from flies to humans. The cDNA encoding the hamster protein was isolated by using mixed oligonucleotides deduced from peptide sequences. The 359-amino acid protein is the hamster homologue of the recently reported murine and human EMAP II cytokine implicated in a variety of inflammatory disorders. The sequence of several proEMAP II proteins suggests that the p43 component of the complex is the precursor of the active mature cytokine after cleavage at a conserved Asp residue. The COOH-terminal moiety of p43 is also homologous to polypeptide domains found in bacterial methionyl-or phenylalanyl-tRNA synthetases and in the yeast Arc1p/G4p1 protein that associates with yeast methionyl-tRNA synthetase. Our results implicate the COOH-terminal moiety of p43 as a RNA binding domain. In the native state, as a component of the multisynthetase complex, p43 may be required for tRNA channeling and, after proteolytic processing occurring in tumor cells, would acquire inflammatory properties possibly related to apoptosis. The release of a truncated p43 from the complex could be involved in mediation of the signaling of tumor cells and stimulation of an acute inflammatory response.Aminoacyl-tRNA synthetases catalyze the activation of their cognate amino acid and transfer to the relevant tRNA. In mammals, this family of enzyme contributes two distinct high molecular mass structures: a complex made of nine synthetases and a complex involving valyl-tRNA synthetase and the ␣, ␤, ␥, and ␦ subunits of elongation factor 1. The ten other aminoacyltRNA synthetases are generally described as free enzymes (1-3). The multisynthetase complex contains the nine aminoacyl-tRNA synthetase activities for amino acids Glu, Pro, Ile, Leu, Met, Gln, Lys, Arg, and Asp and the three auxiliary proteins with masses of 18, 38, and 43 kDa. It is ubiquitous to all coelomate metazoan species from arthropods to humans (4). Immunoprecipitation experiments demonstrated the tight association of all of these components (5-7). Electron microscopy studies showed a fairly elongated U-shaped structure (8). Although the three nonsynthetase components were invariably encountered in this complex, their structural or functional role within this multi-subunit structure was not established.We have recently reported the cloning of the cDNA encoding the p18 component of the complex (9). It shares sequence homology with a protein domain recovered in the NH 2 -terminal polypeptide extension of human valyl-tRNA synthetase and in the NH 2 -terminal domains of the ␤ and ␥ subunits of elongation factor 1. In the valyl-tRNA synthetase⅐EF-1H complex, this domain has been involved in protein-protein interaction between the ␤ and ␥ subunits of the eukaryotic elongation factor EF-1H (10) or between valyl-tRNA synthetase and EF-1H (11). This led us to suggest that p18 is involved in anchoring the multisynthetase complex to th...

No abstract

Recently, we demonstrated that the expression levels of the translationally controlled tumor protein (TCTP) were strongly down-regulated at the mRNA and protein levels during tumor reversion͞suppression and by the activation of p53 and Siah-1. To better characterize the function of TCTP, a yeast two-hybrid hunt was performed. Subsequent analysis identified the translation elongation factor, eEF1A, and its guanine nucleotide exchange factor, eEF1B␤, as TCTP-interacting partners. In vitro and in vivo studies confirmed that TCTP bound specifically eEF1B␤ and eEF1A. Additionally, MS analysis also identified eEF1A as a TCTP interactor. Because eEF1A is a GTPase, we investigated the role of TCTP on the nucleotide exchange reaction of eEF1A. Our results show that TCTP preferentially stabilized the GDP form of eEF1A, and, furthermore, impaired the GDP exchange reaction promoted by eEF1B␤. These data suggest that TCTP has guanine nucleotide dissociation inhibitor activity, and, moreover, implicate TCTP in the elongation step of protein synthesis.