Nucleotide Sequence of a Region in 23‐S RNA Adjacent to Peptidyl Transferase Catalytic Center of Escherichia coli Ribosomes

N-Iodoacetylphenylalanyl-tRNAPhe was used as an affinity label to localize the RNA components intimately involved in the catalytic center of Escherichia coli ribosomes. This analogue could alkylate the specific region of 23-S RNA that waslocated within 2000 nucleotides from the 3' terminus of the molecule. Sequence analysis revealed that the alkylation by the active substrate (N-iodoacetylphenylalanyl-tRNAPhe) was directed to 5'-terminal adenosine residue of a heptanucleotide, A-U-U-U-U-A-Gp, which seemed to be derived from a heptadecanucleotide, U-U-A-A-A-A-A-C-A-C-A-U-U-U-U-A-Gp, in the original 23-S RNA. The significance of the unique sequence in the ribosomal functions is discussed.