A post-translational modification in the GGQ motif of RF2 from Escherichiacoli stimulates termination of translation

A post-translational modification affecting the translation termination rat e was identified in the universally conserved GGQ sequence of release facto r 2 (RF2) from Escherichia coli, which is thought to mimic the CCA end of t he tRNA molecule. It was shown by mass spectrometry and Edman degradation t hat glutamine in position 252 is N-5-methylated. Overexpression of RF2 yiel ds protein lacking the methylation. RF2 from E.coli K12 is unique in having Thr246 near the GGQ motif, where all other sequenced bacterial class 1 RFs have alanine or serine, Sequencing the prfB gene from E.coli B and MRE600 strains showed that residue 246 is coded as alanine, in contrast to K12 RF2 , Thr246 decreases RF2-dependent termination efficiency compared with Ala24 6, especially for short peptidyl-tRNAs, Methylation of Gln252 increases the termination efficiency of RF2, irrespective of the identity of the amino a cid in position 246, We propose that the previously observed lethal effect of overproducing E.coli K12 RF2 arises through accumulating the defects due to lack of Gln252 methylation and Thr246 in place of alanine.