Transfer RNA (tRNA) interacts with high specificity with a number of other cellular components including the aminoacyl-tRNA synthetases, the messenger RNA-ribosome complex, and the protein factors concerned with the processes of peptide chain initiation and elongation. Although the primary structures of several tRNA's from both pro- and eucaryotic cells have been determined, the base sequences within the primary structure which determine the specificity of these various interactions have proved elusive. An understanding of the relationship between the structure and function of tRNA at this level is likely to be a necessary prerequisite to an appreciation of the role of this macromolecule in cellular regulatory processes which may, by their malfunctioning, transform a normal to a cancer cell. The recognition sites are of two types, those common to all tRNA's (type I) and those specific for each individual species of tRNA (type II). The goal of this proposed program is to identify one example of each class of sites by looking for ribonuclease-resistant regions in complexes of tRNA with an amino-acyl- tRNA synthetase (type II) and with the enzyme CTP(ATP)-tRNA nucleotidyl- transferase (type I). P32-Labelled E. coli will be cultured and purified species of tRNA will be isolated by column chromatography. The aminoacyl-tRNA synthetase and nucleotidyltransferase enzymes will be isolated from the high speed supernatant fraction of E. coli by standard chromatographic procedures. Complexes between the tRNA and the synthetase/nucleotidyltransferase will be isolated by either sucrose density gradient centrifugation or sucrose gradient electrophoresis and these complexes will then be treated with nucleases. The oligonucleotide fragments will be analysed by 2-dimensional high voltage electrophoresis.