TERNARY COMPLEX BETWEEN ELONGATION-FACTOR TU-CENTER-DOT-GTP AND PHE-TRNA(PHE)

The effect of aminoacylation and ternary complex formation with elonga tion factor Tu.GTP on the tertiary structure of yeast tRNA(Phe) was ex amined by H-1-NMR spectroscopy. Esterification of phenylalanine to tRN A(Phe) does not lead to changes with respect to the secondary and tert iary base pair interactions of tRNA. Complex formation of Phe-tRNA(Phe ) with elongation factor Tu.GTP results in a broadening of all imino p roton resonances of the tRNA. The chemical shifts of several NH proton resonances are slightly changed as compared to free tRNA, indicating a minor conformational rearrangement of Phe-tRNA(Phe) upon binding to elongation factor Tu.GTP. All NH proton resonances corresponding to th e secondary and tertiary base pairs of tRNA, except those arising from the first three base pairs in the aminoacyl stem, are detectable in t he Phe-tRNA(Phe).elongation factor Tu GTP ternary complex. Thus, altho ugh the interactions between elongation factor Tu and tRNA accelerate the rate of NH proton exchange in the aminoacyl stem-region, the Phe-t RNA(Phe) preserves its typical L-shaped tertiary structure in the comp lex. At high (> 10(-4) M) ligand concentrations a complex between tRNA (Phe) and elongation factor Tu.GDP can be detected on the NMR time-sca le. Formation of this complex is inhibited by the presence of any RNA not related to the tRNA structure. Using the known tertiary structures of yeast tRNA(Phe) and Thermus thermophilus elongation factor Tu in i ts active, GTP form, a model of the ternary complex was constructed.