Fig. 3.

A possible mechanistic model for the peptide release. Upon stop-codon recognition, class I RFs coordinate with the active site of the ribosome to create a tightly packed catalytic pocket. The highly conserved 23S rRNA nucleotide A2602 is likely involved in stabilizing the GGQ motif. The catalytic water molecule is coordinated by the 2′ OH of the A76 and the Q240 to launch a nucleophilic attack on the carbonyl carbon of the ester linkage. The hydrolytic chemical reaction likely proceeds through a concerted proton shuttle mechanism involving 2′ OH of the A76 that is the similar to the one employed in peptide bond formation (21, 22, 25).