Three-dimensional reconstruction of the valyl-tRNA synthetase/elongation factor-1H complex and localization of the delta subunit.

Eukaryotic valyl-tRNA synthetase (ValRS) and the heavy form of elongation factor 1 (EF-1H) are isolated as a stable high molecular mass complex that catalyzes consecutive steps in protein biosynthesis--aminoacylation of tRNA and its transfer to elongation factor. Herein is the first three-dimensional structure of the particle as calculated from electron microscopic images of negatively stained samples of the human ValRS/EF-1H complex. The ca. 12 x 8 nm particle has two distinct domains and each appears to have twofold symmetry. Bound antibodies place two delta subunits near the particle's center. These data support a dimeric head-to-head arrangement of particle components.