A complex from cultured Chinese hamster ovary cells containing nine aminoacyl‐tRNA synthetases

Abstract

The size distribution of the 20 aminoacyl-tRNA synthetses from wild-type Chinese hamster ovary (CHO) cells and from the mutant cell line tsH1, containing a temperature-sensitive leucyl-tRNA synthetase, was determined by gel filtration. Nine aminoacyl-tRNA synthetases, specific for arginine, aspartic acid, glutamic acid, glutamine, isoleucine, leucine, lysine, methionine and proline, which coeluted as high-M_r entities (M_r∼ 1.2 × 10⁶), were further co-purified to yield a multienzyme complex, the polypeptide composition of which was identical to that previously determined for the complex from rabbit liver. Immunoprecipitates obtained from crude extracts of wild-type and tsH1 mutant cells, using specific antibodies directed to the lysyl-tRNA or methionyl-tRNA synthetase components of the complex, displayed the same polypeptide compositions as that of the purified complex, thereby establishing the heterotypic nature of this complex. Although the activity of leucyl-tRNA synthetase from the mutant cells, grown at a permissive temperature, was low compared to that from the wild-type, the polypeptide of M_r 129000, corresponding to this enzyme, was present in similar amounts and occurred exclusively as a component of the high-M_r complex. Finally, we report that attempts to demonstrate phosphorylation of the components of the complex from cultured CHO, HeLa and C3 cells were unsuccessful.