POSSIBLE INVOLVEMENT OF PEPTIDYL TRANSFERASE IN TERMINATION STEP OF PROTEIN BIOSYNTHESIS

The ability of a cell-free ribosomal system to release nascent peptide in the presence of a termination codon and release factor has been found to run parallel with the ability of the 5OS ribosomal subunit to synthesize peptide bonds (peptidyl transferase activity). The evidence is of two kinds. (a) Use was made of the recent-finding that the peptidyl transferase activity of the 50S subunit can be abolished and subsequently restored by relatively mild treatments. We have found that the release reaction responds similarly: that is, inactivation of the 50S subunit eliminated both activities; reactivation restored both, and partial reactivation restored both partially and to the same degree, (b) A number of antibiotics that inhibited the peptidyl transferase activity of the 50S subunit also inhibited the release activity, and with the same dependence on antibiotic concentration. These results indicate that a component of the 50S ribosomal subunit that participates in the peptide-bond-forming step of chain extension may also participate in the release step of chain termination. They suggest, but do not unequivocally prove, that this component is the ribosomal enzyme peptidyl transferase, operating with an altered specificity, so as to transfer nascent peptide to water instead of to aminoacyl transfer ribonucleic acid. © 1969, American Chemical Society. All rights reserved.