Studies on the Formation of Transfer Ribonucleic Acid-Ribosome Complexes, XII. Phenylalanyl-Oligonucleotide Binding to E. coli Ribosomes: Necessity for a Free Amino Group

The binding of phenylalanyl-oligonucleotide, C-A-C-C-A-(Phe), to ribosomes requires the presence of a free amino group on the amino acid. Acetylation of the amino acid reduces the binding to ribosomes to about 1/20 of the binding observed with the intact Phe-oligonucleotide. Deacylation of the phenylalanyl-oligonucleotide eliminates binding of the free amino acid and markedly reduces the binding of the oligonucleotide (C-A-C-C-A). Neither 30S nor 50S subunits alone are sufficient for binding of the phenylalanyl-oligonucleotide; the presence of both subunits is necessary. The data suggest that phenylalanyl-oligonucleotide binding to ribosomes represents the binding of the aminoacyl-terminus of phenylalanyl-tRNA and that the presence of an amino acid with an unsubstituted amino group attached to the oligonucleotide (C-A-C-C-A) is required for binding to this potassium-dependent site. Furthermore, the ribosome itself has the capability of distinguishing between aminoacyl-oligonucleotides with N-substituted and unsubstituted amino acids-