Fluorescent tRNA derivatives and ribosome recognition.

The use of fluorescent derivatives of tRNAPhe (yeast) in studies on tRNA conformation and on tRNA-ribosome recognition is described. Evidence is presented which indicates that under physiological conditions with respect to ionic strength and Mg2+ concentration, tRNAPhe exists in at least two conformations. The functional significance of this behavior is discussed on the basis of aminoacylation experiments. The investigation of the ribosome complexes of tRNAPhe labeled in the anticodon and D-loops has provided evidence suggesting that the presence of the codon, although not appreciably altering the apparent association constant, leads to qualitatively different complexes in which the tRNA appears to be rigidly bound to the codon even in the P-tRNA to the ribosome occurs in several steps, which take place only in the presence of the proper codon. One or more of these steps may represent codon-induced conformational changes of the tRNA molecule, which constitute the molecular basis of the highly specific binding of the tRNA to the ribosome.