title: Action of erythromycin and virginiamycin S on polypeptide synthesis in cell-free systems.
abstract: Erythromycin (a 14-membered macrolide) and virginiamycin S (a type B synergimycin) block protein biosynthesis in bacteria, but are virtually inactive on poly(U)-directed poly(Phe) synthesis. We have recently shown, however, that these antibiotics inhibit the in vitro polypeptide synthesis directed by synthetic copolymers: this effect is analyzed further in the present work. We were unable to find any consistent alteration produced by these antibiotics on coupled and uncoupled EF-G- and EF-Tu-dependent GTPases, on the EF-Tu-directed binding of aminoacyl-tRNA to ribosomes, and on the EF-G- and GTP-mediated translocation of peptidyl-tRNA bound to poly(U,C).ribosome complexes. With these complexes, the peptidyl transfer reaction, as measured by peptidylpuromycin synthesis, was 10-30% inhibited by virginiamycin S and erythromycin. A direct relationship between the virginiamycin S- and erythromycin-promoted inhibition of poly(A,C)-directed polypeptide synthesis, on the one hand, and the EF-G concentration and the rate of the polymerization reaction, on the other hand, was observed, in agreement with a postulated reversible inhibitor action of these antibiotics. The increased inhibitory activity, which was observed during the first 4-6 rounds of elongation, in the presence of virginiamycin S or erythromycin, was suggestive of a specific action of these antibiotics on the correct positioning of peptidyl-tRNA at the P site. The marked stimulation of premature release of peptidyl-tRNA from poly(A,C).ribosome complexes can be referred to an altered interaction of the C-terminal aminoacyl residue of the growing peptidyl chain with the ribosome. We conclude that the action of virginiamycin S and erythromycin entails a template-dependent alteration of the interaction of peptidyl-tRNA with the donor site of peptidyltransferase, which may lead to a transient functional block of the ribosome and in some instances to a premature release of peptidyl-tRNA and termination of the elongation process.
mesh_terms: D004917:Erythromycin / Q000494:pharmacology*; D004926:Escherichia coli / Q000187:drug effects / Q000378:metabolism*; D020963:GTP Phosphohydrolase-Linked Elongation Factors / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D010452:Peptide Biosynthesis; D010441:Peptide Chain Elongation, Translational / Q000187:drug effects; D020653:Peptide Elongation Factor G; D010444:Peptide Elongation Factor Tu / Q000494:pharmacology; D010445:Peptide Elongation Factors / Q000494:pharmacology; D011061:Poly A / Q000378:metabolism; D011066:Poly C / Q000378:metabolism; D011072:Poly U / Q000378:metabolism; D011691:Puromycin / Q000378:metabolism; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism; D014769:Virginiamycin / Q000494:pharmacology*
chemical_list: D020653:Peptide Elongation Factor G; D010445:Peptide Elongation Factors; D012346:RNA, Transfer, Amino Acyl; C023512:elongation factor Ts; D014769:Virginiamycin; D011061:Poly A; C035610:poly(U-C); D011072:Poly U; C023794:poly(A-C); D011066:Poly C; D011691:Puromycin; D004917:Erythromycin; D006160:Guanosine Triphosphate; D020963:GTP Phosphohydrolase-Linked Elongation Factors; D010444:Peptide Elongation Factor Tu