CONFORMATIONAL TRANSITIONS OF A TRANSFERRNA-AMINOACYL-TRANSFERRNA SYNTHETASE COMPLEX INDUCED BY TRANSFERRNAS BEARING DIFFERENT MODIFICATIONS IN THE 3' TERMINUS

The influence of modifications of the 3'-terminal adenosine of tRNAPhe (yeast) on the complex formation between this tRNA and phenylalanyl-tRNA synthetase (yeast) has been investigated by using fluorescence titrations and fast kinetic techniques. Subtle changes in the 3' terminus are reflected by distinct alterations in the two-step recognition process which had been demonstrated earlier for the native substrate tRNAPheCCA [Krauss, G., Riesner, D., & Maass, G. (1977) Nucleic Acids Res. 4, 2253-2262]. Binding experiments With tRNAPhecc, tRNAPhecCA-ox-red, tRNAPbecc2'dA, tRNAPheCC3,dA, tRNAphtcc.formycin, and tRNAPhecc.formyciMx.red confirm that the 3'-terminal adenosine participates in a conformational change of the tRNA-synthetase complex. This@r@nis valid in both the absence and presence of phenylalaninyl-5'-AMP, the alkyl analogue of the aminoacyladenylate. As compared to tRNAPheCCA, a slower conformational change is observed with the competitive inhibitor tRNAphe cc-formycm-ox-red-The reaction enthalpy and/or the quench of the Y-base fluorescence that accompany the conformational change are altered upon binding of tRNAPheC2'dA, tRNApheCC3dA, and tRNAPhe ccformyciir Itevsident that the final adaptation between tRNA and its synthetase in the complex is determined by the chemical nature of the 3'-terminal nucleotide. This is of vital importance for the specificity of the aminoacylation process. © 1979, American Chemical Society. All rights reserved.