Effects of some inhibitors of protein synthesis on the binding of aminoacyl tRNA to ribosomal subunits

Abstract

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. Polynucleotide-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 extent of binding with 30-S subunits is increased by addition of 50-S subunits. 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 aminoacyl-tRNA binding. They partially inhibit the 50-S phase in the phenylalanine 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 II ( 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 dextran sulphate are potent inhibitors of both 30-S and 50-S phases of binding. Guanylylmethylene diphosphonate 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.