Peptidyl transferase is an integral part of the large subunit of ribosomes and catalyzes peptide-bond formation in the elongation step of translation during protein biosynthesis. Peptide-bond formation involves an acyl group O-to-N migration and converts an ester to an amide. Peptidyl-transfer RNA in the P site is the ester bond of high energy content that donates its peptidyl group to the amino group of aminoacyl-tRNA bound in the A site of the ribosome. The peptidyl transferase reaction is often measured by the puromycin reaction, in which puromycin acts as the acceptor substrate to form peptidyl-puromycin. In bacteria, peptidyl transferase activity can be detected in the 50 S ribosomal subunit, and several ribosomal proteins are thought to play a role in the activity. The primary activity of peptidyl transfer, however, is a ribozyme activity encoded in the 23 S rRNA. The peptidyl transferase activity of Escherichia coli and Thermus aquaticus ribosomes are resistant to conventional protein extraction procedures (1), and the formation of a G-C pair between G2252 in the conserved hairpin loop of E. coli 23 S rRNA and C74 in the 3′-terminal region of tRNA is a prerequisite for the peptidyl transfer reaction. These findings suggest that not all the large subunit proteins are necessarily required for peptidyl transferase activity. It has been shown recently that E. coli 23 S rRNA synthesized by in vitro transcription with T7 RNA polymerase exhibits the primary peptidyl transfer activity in the absence of any ribosomal proteins in vitro, and that the truncated domain V transcript alone has this activity (2).
Peptidyl transferase is also involved in the termination reaction of protein synthesis and hydrolyzes the ester bond between the peptide chain and tRNA at the P site of the ribosome (see Release Factor). Peptidyl transferase is inhibited by various antibiotics, such as chloramphenicol, lincomycin, carbomycin (prokaryotes), and cycloheximide (eukaryotes).
