Tests of the ribosome editor hypothesis. III. A mutant Escherichia coli with a defective ribosome editor.

Peptidyl-tRNA dissociates from the ribosomes of Escherichia coli during protein biosynthesis. The ribosome editor hypothesis states that incorrect peptidyl-tRNAs dissociate preferentially. Editing would therefore prevent the completion of proteins containing misincorporated amino acids. We have isolated a mutant strain of E. coli that dissociates some peptidyl-tRNAs at a fivefold lower rate than its parent strain, and that synthesizes significantly more erroneous complete proteins. This strain is also partially resistant to the antibiotic erythromycin, which in wild-type E. coli stimulates the dissociation of peptidyl-tRNA from ribosomes. The data suggest that in this mutant all peptidyl-tRNAs are bound to the ribosome more tightly than normally during protein synthesis. Because of the inverse correlation between the accuracy of synthesis of complete proteins and the rate of dissociation of peptidyl-tRNA from the ribosome, we propose that the mutant contains a defective ribosomal editor.