Isolation and electron microscopic characterization of the high molecular mass aminoacyl-tRNA synthetase complex from murine erythroleukemia cells

A high molecular mass aminoacyl-tRNA synthetase complex has been isolated from a murine erythroleukemia cell line. This multienzyme complex contains activities for the arginyl-, aspartyl-, glutamyl-, glutaminyl-, isoleucyl,- leucyl-, lysyl-, methionyl-, and prolyl-tRNA synthetases. This enzyme composition, the polypeptide pattern observed upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the relative stoichiometry of the component polypeptides are characteristic of high molecular mass complexes of aminoacyl-tRNA synthetases isolated from a variety of mammalian tissues and cell types. Negatively stained preparations of native complex and of glutaraldehyde-treated material have been examined by electron microscopy. In both cases, a distinctive particle is observed which appears in several orientations. The most common views are of two different projections of a squarish particle that measures approximately 27 x 27 nm. Other commonly observed views are of a "U" shape, a rectangle, and a triangle. All of these views are seen in both gradient-purified samples and those prepared directly from material as isolated. These data are consistent with a model for the multienzyme aminoacyl-tRNA synthetase complex as a "cup" or elongated U structure. These studies demonstrate that the high molecular mass complex of eukaryotic aminoacyl-tRNA synthetases does have a coherent structure that can be visualized by electron microscopy.