Localization of the binding site for the 3'-terminal sequence of tRNAPhe in subunits of phenylalanyl-tRNA synthetase from Thermus thermophilus.

A photoreactive tRNAPhe derivative containing a 4-thiouridine residue at the 3'-end (tRNAPhe-s4U-75) was prepared by tRNA nucleotidyltransferase-mediated incorporation of s4UMP into a tRNAPhe transcript lacking the 3'-terminal dinucleotide. The resulting tRNAPhe-s4U-75 was covalently bound to phenylalanyl-tRNA synthetase from Thermus thermophilus, and all criteria of an affinity modification were met. The main products of modification displaying various electrophoretic mobilities were formed by binding tRNAPhe-s4U-75 to the beta-subunit (major) of the enzyme. These data suggest that the nucleotide found at position 75 of tRNAPhe interacts with the beta-subunit of phenylalanyl-tRNA synthetase.