Identification of proteins involved in the peptidyl transferase activity of ribosomes by chemical modification.

Photochemical oxidation of Escherichia coli 50 S ribosomal subunits in the presence of methylene blue or Rose Bengal causes rapid loss of peptidyl transferase activity. Reconstitution experiments using mixtures of components from modified and unmodified ribosomes reveal that both RNA and proteins are affected, and that among the proteins responsible for inactivation there are both LiCl-split and core proteins. The proteins L2 and L16 from the split fraction and L4 from the core fraction of unmodified ribosomes were together nearly as effective as total unmodified proteins in restoring peptidyl transferase activity to reconstituted ribosomes when added with proteins from modified ribosomes. These three proteins are therefore the most important targets identified as responsible for loss of peptidyl transferase activity on photo-oxidation of 50 S ribosomal subunits.