Aminoacyl-tRNA synthetases (ARSs) ligate amino acids to their cognate tRNAs. It has been suggested that mammalian ARSs are linked to the EF-1 complex for efficient channeling of aminoacyl tRNAs to ribosome. Here we systemically investigated possible interactions between human ARSs and the subunits of EF-1 (alpha, beta, gamma, and delta) using a yeast two-hybrid assay. Among the 80 tested pairs, leucyl- and histidyl-tRNA synthetases were found to make strong and specific interaction with the EF-1gamma and beta while glu-proly-, glutaminyl-, alanyl-, aspartyl-, lysyl-, phenylalanyl-, glycyl-, and tryptophanyl-tRNA synthetases showed moderate interactions with the different EF-1 subunits. The interactions of leucyl- and histidyl-tRNA synthetase with the EF-1 complex were confirmed by immunoprecipitation and in vitro pull-down experiments. Interestingly, the aminoacylation activities of these two enzymes, but not other ARSs, were stimulated by the cofactor of EF-1, GTP. These data suggest that a systematic interaction network may exist between mammalian ARSs and EF-1 subunits probably to enhance the efficiency of in vivo protein synthesis. (C) 2002 Elsevier Science (USA).