lsomeric Phenylalanyl-tRNAs. Position of the Aminoacyl Moiety During Protein Biosynthesis

The preparation of phenylalanyl-tRNA terminating in 3'-deoxyadenosine has been achieved by incubation of abbreviated tRNA (tRNA-CpC(OH)) with 3'-deoxyadenosine 5'-diphosphate and polynucleotide phosphorylase (EC 2.7.7.8), followed by aminoacylation. The isomeric phenylalanyl-tRNA terminating in 2'-deoxyadenosine was constructed by incubation of tRNA-CpC(OH) with 2'-deoxy-3'-O-phenylalanyladenosine 5'-diphosphate and polynucleotide phosphorylase. While tRNA is aminoacylated at the 2'-position, only the 3'-aminoacyl-tRNA is active as a peptide acceptor in the peptidyltransferase reaction. Both modified tRNAs were bound to the A-site as efficiently as unmodified tRNA, but neither was so efficient at P-site binding or as an acceptor in the peptidyltransferase reaction. Neither of the modified tRNAs acted as a donor in the peptidyltransferase reaction.