(photoaffinity labeling/aromatic ketones/tRNA binding site/hybridiz.

Benzoylphenyl)propionyl(3H)Phe- tRNA bound to the peptidyl site of the ribosome is photo- crosslinked exclusively to 23S RNA on irradiation at 320 nm. The site of reaction has been identified both by hybridization and primer-extension experiments as uridine-2584 and uri- dine-2585, located within the central loop of domain V accord- ing to the secondary structure model of 23S RNA. The fact that the covalently crosslinked tRNA retains its ability to form a peptide bond, together with the proximity of this site to the position of several mutations leading to chloramphenicol or erythromycin resistance strongly argue that this region of the 23S-like rRNAs is an integral component of the peptidyl transferase site. On the basis of these results, and from comparative analysis of the 16 available large subunit rRNA sequences, we propose a model for the functional organization of the peptidyl transferase site involving interaction of do- mains II and V of 23S rRNA.