The codon specificity of eubacterial release factors is determined by the sequence and size of the recognition loop

An explanation for how the recognition loops of RF1 and RF2 maintain specificity. (A) The recognition loop residues responsible for E. coli RF codon specificity. Residues that are important for determining the different specificities of RF1 and RF2 at the second and third positions of the stop codon are indicated. (B) The isolated and ribosome-bound structures of the RF1 and RF2 recognition loops RF1 (Graille et al. 2005; Laurberg et al. 2008) and RF2 (Vestergaard et al. 2001; Weixlbaumer et al. 2008) with key elements highlighted (residues) or annotated (helices and strands).