Hygromycin A, a novel inhibitor of ribosomal peptidyltransferase

In cell-free systems from Escherichia coli, hygromycin A inhibits polypeptide synthesis directed by either poly(U) or phage R 17 RNA, and the reaction of puromycin with either natural peptidyl-tRNA, or AcPhe-tRNA, or the 3'-terminal fragment of AcLeu-tRNA (C-A-C-C-A-LeuAc). In contrast, the antibiotic does no inhibit the enzymatic binding of Phe-tRNA to ribosomes or the translocation of AcPhe-tRNA. It is concluded that hygromycin A is a specific inhibitor of the peptide bond formation step of protein synthesis. The action of hygromycin A on peptidyl transfer is similar to that of chloramphenicol, an antibiotic that shares some common structural features with hygromycin A. Both antibiotics inhibit the binding of C-A-C-C-A-Leu to the acceptor site of peptidyl transferase and stimulate that of C-A-C-C-A-LeuAc to the donor site of the enzyme. Moreover, hygromycin A blocks the binding of chloramphenicol to ribosomes, indicating that the binding sites of the antibiotics may be closely related. Hygromycin A is a more potent agent than chloramphenicol and binds quite strongly to ribosomes.