Fig. 5.
Model for ribosome stalling at PPX and XPP motifs. (A) Translation stalls at PPX motifs with the peptidyl-Pro-Pro-tRNA in the P-site and aminoacyl-tRNA bearing the amino acid X in the A-site. (B) Peptide bond formation between NH2 of amino acid X in the A-site with the carbonyl carbon of the Pro-tRNA in the P-site. (C) Translation stalls at XPP motifs with the peptidyl-X-Pro-tRNA in the P-site and Pro-tRNA in the A-site. (D) Peptide bond formation between imino group of Pro in the A-site with the carbonyl carbon of the peptidyl-X-Pro-tRNA in the P-site.