EFFECTS OF SOME INHIBITORS OF PROTEIN SYNTHESIS ON BINDING OF AMINOACYL TRNA TO RIBOSOMAL SUBUNITS

Some 30 compounds have been selected which inhibit polypeptide synthesis from aminoacyl tRNA in 70-S ribosomal systems. The compounds fall into chemically related groups and are further classified into categories according to their action on chloramphenicol binding to 50-S ribosomal subunits. Poly-nucleotide-directed binding of phenylalanyl tRNA, lysyl tRNA and prolyl tRNA to Escherichia coli ribosomes has been studied. Isolated 30-S but not 50-S subunits support aminoacyl-tRNA binding. The ex-tent of binding with 30-S subunits is increased by addition of 50-S sub-units. Effects of the inhibitors on the two phases of binding are reported. Category-I (compounds which inhibit chloramphenicol binding). Chloramphenicol, chloramphenicol analogues, macrolides, lincomycin, celesticetin and streptogramin-A do not affect the 30-S phase of amino-acyl-tRNA binding. They partially inhibit the 50-S phase in the pheny-lalanine but not in the lysine or proline systems. It is probable that all Category-I compounds act in a related manner, through interaction with the 50-S subunit. The primary reaction inhibited by such interaction remains to be elucidated. Category-n (compounds which weakly inhibit chloramphenicol binding to ribosomes). Puromycin and its analogues weakly inhibit both 30-S and 50-S phases of aminoacyl-tRNA binding. This effect is probably unrelated to the reaction of puromycin with nascent peptides. Categorie-III (compounds which do not inhibit chloramphenicol binding). Streptogramin-B and related antibiotics stimulate aminoacyl-tRNA binding to ribosomes. The effect is localized to the 30-S phase of binding. Amicetin also stimulates aminoacyl-tRNA binding to 70-S ribosomes but has little effect on binding with separated or re-combined ribosomal subunits. Tetracycline partially inhibits both 30-S and 50-S phases of binding, whereas gougerotin and sparsomycin have little or no effect on either phase. Edeine and dex-tran sulfate are potent inhibitors of both 30-S and 50-S phases of binding. Guanylylmethylene disphosphonate weakly inhibits the 30-S but not the 50-S phase of binding. It is concluded that the 30 odd inhibitors fall into a number of functionally distinct groups. Most of the compounds inhibit protein synthesis through interaction with components on one or other of the ribosomal subunits.