Identification of a region in 23S rRNA located at the peptidyl transferase center.

A photolyzable derivative of dipeptidyl-tRNA, p-azido-N-tBoc-Phe-[3H]Phe-tRNA, bound reversibly to 70S ribosomes in the presence of poly(U), becomes, when irradiated, covalently attached to components of the 50S ribosomal subunit. Most of the reaction occurs within the 23S RNA, while ribosomal proteins are only weakly labeled. Reversible binding as well as the covalent reaction are reduced in the absence of poly(U) or in the presence of several antibiotics specific for the 50S ribosomal subunit. There are apparently few sites (or perhaps a single site) of reaction on the 23S RNA that are exclusively located within the 2000 nucleotides from the 3 terminus of the molecule. Part of the 23S RNA within this region must therefore be closely associated with the peptidyl transferase center of the ribosome.