Fig. 4.

Close-up view of the decoding center of the small ribosomal subunit taken from an atomic resolution structure (2.8 Å) of the a pre-translocation complex of the 70S bacterial ribosome with bound mRNA and aminoacyl tRNA^Phe in the A-site, deacylated initiator tRNA^fMet in the P-site and non-cognate tRNA in the E-site (Selmer et al., 2006) (PDB 2J02). (A) Aminoacyl A-site and deacylated P-site tRNA anticodon–mRNA codon interactions are shown. A Mg²⁺ ion is also shown which may help induce a kink if the mRNA and therefore maintain reading frame just prior to translocation. (B) Close-up of the P- and E-site tRNA codon regions within the decoding center, highlighting the displacement of the P-site tRNA codon toward the A-site. See text for details. Adapted from Selmer et al. (2006).