Translation requires the specific attachment of amino acids to tRNAs by aminoacyl-tRNA synthetases (aaRSs) and the subsequent delivery of aminoacyl-tRNAs to the ribosome by elongation factor 1 alpha (EF-1alpha). Interactions between EF-1alpha and various aaRSs have been described in eukaryotes, but the role of these complexes remains unclear. To investigate possible interactions between EF-1alpha and other cellular components, a yeast two-hybrid screen was performed for the archaeon Methanothermobacter thermautotrophicus. EF-1alpha was found to form a stable complex with leucyl-tRNA synthetase (LeuRS; K(D) = 0.7 microM). Complex formation had little effect on EF-1alpha activity, but increased the k(cat) for Leu-tRNA(Leu) synthesis approximately 8-fold. In addition, EF-1alpha co-purified with the archaeal multi-synthetase complex (MSC) comprised of LeuRS, LysRS and ProRS, suggesting the existence of a larger aaRS:EF-1alpha complex in archaea. These interactions between EF-1alpha and the archaeal MSC contribute to translational fidelity both by enhancing the aminoacylation efficiencies of the three aaRSs in the complex and by coupling two stages of translation: aminoacylation of cognate tRNAs and their subsequent channeling to the ribosome.