Antibiotics

Several antibiotics that inhibit the peptidyl transferase activity of ribosomes bind directly to the peptidyl transferase centre of the 23S rRNA. Single base mutations in the antibiotic binding sites results in antibiotic resistance. Naked 23S rRNA retains peptidyl transferase activity. Colicin E3 is a protein that inhibits growth of bacterial cells that lack the Col plasmid. It acts by cleaving 16S rRNA 50 nucleotides from its 3’ end. The cleaved fragment contains the a stretch of ~6 nucleotides complementary to the ribosome binding site of the mRNA. Hence ribosomes cannot initiate protein synthesis. The ribotoxins ricin and α-sarcin both act on a conserved stem-loop structure in 28S rRNA involved in binding aminoacyl tRNA and inhibit protein synthesis. Ricin removes a single adenine residue, α-sarcin causes a single cleavage in the sugar-phosphate backbone.