 A class 1 RF recognizes the stop codon and promotes the hydrolysis of the ester bond linking the polypeptide chain with the peptidyl site tRNA, a reaction catalyzed at the peptidyl transferase center of the ribosome.Class 2 RFs, which are not codon specific and do not recognize codons, stimulate class 1 RF activity and confer GTP dependency upon the process.In bacteria, both class 1 RFs, RF1 and RF2, recognize UAA; however, UAG and UGA are decoded specifically by RF1 and RF2, respectively.