Ternary complexes of Escherichia coli aminoacyl-tRNAs with the elongation factor Tu and GTP: thermodynamic and structural studies.

The interaction of 18 different Escherichia coli aminoacyl-tRNA species with elongation factor Tu and GTP has been measured by a fluorescence titration assay under equilibrium conditions. The dissociation constants range from 1.9 +/- 0.2.10(-10) M up to 1020 +/- 250.10(-10) M depending on the nucleotide sequence, secondary structure and the chemical composition of the aminoacyl residue of the particular aminoacyl-tRNA. The 'aminoacyl domain' of tRNA consisting of the single stranded, four-nucleotide-long 3'-terminus, aminoacyl stem of seven base-pairs, T-stem and T-loop contains all elements necessary for binding EF-Tu.GTP. The efficiency of aminoacyl-tRNA interaction with EF-Tu.GTP is modulated by the sequence of this 'aminoacyl domain' and by natural modification of its nucleotide residues. An oligoribonucleotide resembling the aminoacyl stem of E.coli tRNA(Ala) and consisting of a four-membered 3'-end, a stem of seven base-pairs and a loop of six nucleotides was prepared by total chemical synthesis on a polymer support. It can be enzymatically aminoacylated by alanine but does not bind in its aminoacylated form to EF-Tu.GTP.