AbstractAfter the experimental verification of Crick's adaptor hypothesis for the role of tRNA, it became apparent that one of the most important of the protein‐nucleic acid interactions occurs at the first step in protein synthesis, namely the amino acid activation reaction. It is here that a specific aminoacyl‐tRNA synthetase must select, with high fidelity, a specific tRNA out of a large collection of molecules of similar size, shape, and overall composition. A mistake at this point, either by esterification of the wrong amino acid to the correct tRNA or by selection of the wrong tRNA, will inevitabley result in the insertion of an amino acid at an incorrect position in a growing polypeptide. Although there are known rules that dictate how one nucleic acid can recognize and interact with another nucleic acid, nothing is known regarding the mechanism by which a specific protein can recognize and interact with a specific nucleic acid. In order to gain some insight into the specific recognition between an aminoacyl‐tRNA synthetase and its cognate tRNA, it became necessary to study the specific interaction with highly purified materials, preferably in gram quantities. An effort to do this for both the synthetases and the tRNA's was launched at the Oak Ridge National Laboratory about 6 years ago. Four high‐resolution column chromatographic procedures have been developed in the ORNL Macromolecular Separations Program for the separation and production of highly purified species of tRNA's. An unexpected “spin‐off” from this program is the analytical use of some of these systems to detect qualitative changes in the tRNA profile of cells as a consequence of virus infection, methionine starvation, and other metabolic alterations.Some examples of the heterologous interaction between aminoacyl‐tRNA synthetases of one species with the tRNA's of another species, and some of the inherent dangers in the interpretation of such interactions, are considered.Finally, some speculations are made regarding the possible role of tRN