The allosteric three-site model for the ribosomal elongation cycle: features and future

The ribosome contains three binding sites for tRNA, viz., the A site for aminoacyl-tRNA (decoding site), the P site for peptidyl-tRNA, and the E site for deacylated tRNA (E for exit). The surprising finding of an allosteric linkage between the E and A sites in the sense of a negative cooperativity has three consequences: (a) it improves the proper selection of aminoacyl-tRNAs while preventing interference from noncognate aminoacyl-tRNAs in the decoding process, (b) it provides an explanation for the ribosomal accuracy without having to resort to the proofreading hypothesis, and (c) it has deepened our understanding of the mode of action of some antibiotics.