Structural investigation of Phe-tRNAPhe from E.coli bound to the ribosomal A-site.

Kethoxal modification of guanosines within Phe-tRNAPhe from E. coli was studied for tRNA in the free state and specifically bound to the ribosomal A-site. Complex formation with the ribosome results in a protection from chemical modification of two distant sites in the tRNA molecule. The guanosines affected are G-18 and G-19, located in the D-loop, and G-34 in the anticodon loop. Modification of Phe-tRNAPhe in the absence of ribosomes leads to a destabilisation of the tRNA structure. Our data are consistent with the conclusion that modification of G-34 at the anticodon loop triggers a conformational instability in distant parts of the tRNA molecule.