Movement of the decoding region of the 16 S ribosomal RNA accompanies tRNAtranslocation

The ribosome undergoes pronounced periodic conformational changes during pr otein synthesis. Of particular importance are those occurring around the de coding site, the region of the 16 S rRNA interacting with the mRNA-(tRNA)(2 ) complex. We have incorporated structural information from X-ray crystallo graphy and nuclear magnetic resonance into cryo-electron microscopic maps o f ribosomal complexes designed to capture structural changes at the translo cation step of the polypeptide elongation cycle. The A-site region of the d ecoding site actively participates in the translocation of the tRNA from th e A to the P-site upon GTP hydrolysis by elongation factor G, shifting appr oximately 8 Angstrom toward the P-site. This implies that elongation factor G actively pushes both the decoding site and the mRNA/tRNA complex during translocation. (C) 2000 Academic Press.