Mechanism of inhibition of protein synthesis by macrolide and lincosamide antibiotics.

During protein synthesis on the ribosome, the growing peptide is linked covalently to a transfer RNA. With a certain probability this peptidyl-tRNA dissociates from the ribosome, whereupon it becomes susceptible to hydrolysis catalyzed by peptidyl-tRNA hydrolase. When placed at nonpermissive temperatures, mutant (pthts) Escherichia coli that are temperature-sensitive for the hydrolase will accumulate peptidyl-tRNA, suffer inhibition of protein synthesis, and eventually die. Treating cells with chloramphenicol before raising the temperature prevents cell death but erythromycin, other macrolides, and lincosamide antibiotics all enhance cell death. Accumulation of peptidyl-tRNA by pthts cells at high temperatures is blocked by chloramphenicol but enhanced by macrolides and lincosamides. The data are most consistent with macrolide and lincosamide antibiotics having as their primary mechanism of inhibition the stimulation of peptidyl-tRNA dissociation from the ribosome. Rather than blocking peptide bond formation or peptidyl-tRNA translocation from the A- to the P-site of the ribosome, these antibiotics allow the synthesis of small peptides which dissociate as peptidyl-tRNAs before being completed. Low doses of erythromycin and lincomycin stimulate preferentially the dissociation of peptidyl-tRNAs that are erroneous. Errors in proteins can be assessed by the time necessary to inactivate beta-galactosidase at > 55 degrees C. Whether erroneous peptidyl-tRNAs are induced by treating E. coli with streptomycin or ethanol, or by starving for an amino acid, the shortened time to inactivate beta-galactosidase is counteracted if the cells are simultaneously treated with erythromycin or lincomycin. In contrast, errors in beta-galactosidase caused by synthesis in the presence of canavanine, an arginine analogue, cannot be counteracted by the simultaneous presence of erythromycin. This result rules out any effect of the drug on post-translational mechanisms of error correction.