THE TERNARY COMPLEX OF EF-TU AND ITS ROLE IN PROTEIN-BIOSYNTHESIS

The past year has seen a breakthrough in our structural understanding of how aminoacyl-tRNAs are selected and transported to the ribosomal A -site in order to decode genetic information contained in messenger RN A. All aminoacyl-tRNAs are recognized by the elongation factor EF-Tu i n prokaryotes or EF-1 alpha in eukaryotes. The recent determination of the structure of the ternary complex of aminoacyl-tRNA, EF-Tu and a G TP analogue shows how the CCA end of all aminoacyl-tRNA structures can be accommodated in a specific binding site on EF-Tu-GTP, and how part of the T-helix can be recognized by EF-Tu in a non-sequence-specific way. Furthermore, the structure of the ternary complex shows striking structural similarity to the structure of another prokaryotic elongati on factor, EF-G, the tRNA translocase, in its GDP or empty form. This observation has led to the proposal of a general macromolecular mimicr y of RNA and protein, which predicts elements of RNA-like structures w ill occur in other translation factors, such as initiation factors and release factors, that interact with similar sites on the ribosome.