Immunoelectron microscopic localization of glutamyl-/prolyl-tRNA synthetase within the eukaryotic multisynthetase complex

A high molecular mass complex of aminoacyl-tRNA synthetases is readily isol ated from a variety of eukaryotes. Although its composition is well charact erized, knowledge of its structure and organization is still quite limited. This study uses antibodies directed against prolyl-tRNA synthetase for imm unoelectron microscopic localization of the bifunctional glutamyl-/prolyl-t RNA synthetase. This is the first visualization of a specific site within t he multisynthetase complex. Images of immunocomplexes are presented in the characteristic views of nega tively stained multisynthetase complex from rabbit reticulocytes. As descri bed in terms of a three domain working model of the structure, in "front" v iews of the particle and "intermediate" views, the primary antibody binding site is near the intersection between the "base" and one "arm," In "side" views, where the particle is rotated about its long axis, the binding site is near the midpoint. "Top" and "bottom" views, which appear as square proj ections, are also consistent with the central location of the binding site. These data place the glutamyl-/prolyl-tRNA synthetase polypeptide in a def ined area of the particle, which encompasses portions of two domains, yet i s consistent with the previous structural model.