SINGLE AMINO-ACID SUBSTITUTION IN PROKARYOTE POLYPEPTIDE RELEASE FACTOR-2 PERMITS IT TO TERMINATE TRANSLATION AT ALL 3 STOP CODONS

Prokaryotic translational release factors, RF1 and RF2, catalyze polyp eptide release at UAG/UAA and UGA/UAA stop codons, respectively. In th is study, we isolated a bacterial RF2 mutant (RF2) containing an E167 K substitution that restored the growth of a temperature-sensitive RF1 strain of Escherichia coil and the viability of a chromosomal RF1/RF2 double knockout. In both in vivo and in vitro polypeptide termination assays, RF2 catalyzed UAG/UAA termination, as does RF1, as well as U GA termination, showing that RF2 acquired omnipotent release activity , This result suggests that the E167K mutation abolished the putative third-base discriminator function of RF2, These findings are interpret ed as indicating that prokaryotic and eukaryotic release factors share the same anticodon moiety and that only one omnipotent release factor is sufficient for bacterial growth, similar to the eukaryotic single omnipotent factor.