THE TERNARY COMPLEX OF AMINOACYLATED TRANSFER-RNA AND EF-TU-GTP - RECOGNITION OF A BOND AND A FOLD

The refined crystal structure of the ternary complex of yeast Phe-tRNA (Phe), Thermus aquaticus elongation factor EF-Tu and the non-hydrolyza ble GTP analog, GDPNP, reveals many details of the EF-Tu recognition o f aminoacylated tRNA (aa-tRNA). EF-Tu-GTP recognizes the aminoacyl bon d and one side of the backbone fold of the acceptor helix and has a hi gh affinity for all ordinary elongator aa-tRNAs by binding to this aa- tRNA motif. Yet, the binding of deacylated tRNA, initiator tRNA, and s elenocysteine-specific tRNA (tRNA(Sec)) is effectively discriminated a gainst. Subtle rearrangements of the binding pocket may occur to optim ize the fit to any side chain of the aminoacyl group and interactions with EF-Tu stabilize the 3'-aminoacyl isomer of aa-tRNA. A general com plementarity is observed in the location of the binding sites in tRNA for synthetases and for EF-Tu. The complex formation is highly specifi c for the GTP-bound conformation of EF-Tu, which can explain the effec ts of various mutants.