Practice question

The Gly-Gly-Gln motif represents the catalytic signature of class I release factors positioned at the tip of the universally conserved GGQ loop that inserts into peptidyl transferase center. In the large subunit, the glutamine side chain is N5-methylated by methyltransferases, allowing precise positioning of a water molecule for nucleophilic attack on the ester bond linking nascent peptide to P-site tRNA, thereby liberating the completed chain during termination. Mutagenesis of GGQ abolishes peptide release while retaining stop codon recognition, demonstrating separation of decoding and catalysis. The motif appears in RF1, RF2, eRF1, and mitochondrial release factors evolutionarily conserved.