Antibiotics as Probes of Ribosome Structure: Binding of Chloramphenicol and Erythromycin to Polyribosomes; Effect of Other Antibiotics

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Abstract
Antibiotics were used as probes of ribosome topology and function. Studies of [ 14 C]chloramphenicol and [ 14 C]erythromycin binding to ribosomes and polyribosomes revealed the following features. The requirement of high K + concentration (150 mM) for [ 14 C]chloramphenicol binding to NH 4 Cl-washed ribosomes resulted from the washing procedure. Neither native 70 S ribosomes nor polyribosomes require K + greater than 30 mM for [ 14 C]chloramphenicol binding. Whereas [ 14 C]chloramphenicol binds to both ribosomes and polyribosomes, [ 14 C]erythromycin binds essentially only to ribosomes. After removal of peptidyl-transfer ribonucleic acid (tRNA) from polyribosomes, [ 14 C]erythromycin could then be bound. The effects of a number of antibiotics on [ 14 C]chloramphenicol binding to ribosomes and polyribosomes was assessed. It was found that most of the macrolides (erythromycin, carbomycin, spiramycin III, niddamycin, oleandomycin, and tylosin) and streptogramins A and B (vernamycin A, PA114A, vernamycin Bα, and PA114B) inhibited chloramphenicol binding to NH 4 Cl-washed and native 70 S ribosomes, but not to polyribosomes. After removal of peptidyl-tRNA from polyribosomes, [ 14 C]chloramphenicol binding was then inhibited. In contrast, sparsomycin and althiomycin inhibited chloram-phenicol binding to polyribosomes, but not to ribosomes. After removal of peptidyl-tRNA from polyribosomes, sparsomycin and althiomycin were then ineffective. The presence of peptidyl-tRNA on polyribosomes apparently is required for binding of sparsomycin and althiomycin, but prevents binding of most macrolides and streptogramins. The lincosaminides (lincomycin and celesticetin) and methymycin (a small macrolide) inhibited [ 14 C]chloramphenicol binding to NH 4 Cl-washed and native 70 S ribosomes best, but also inhibited the binding to polyribosomes. The amino nucleosides and other antibiotics tested do not seem to interact strongly with the major chloramphenicol-binding site. These results provide knowledge of the interrelationships between antibiotic and substrate ribosome binding sites which should eventually contribute to a map of ribosomal topology.