Aminoacylation of tRNA 2′- or 3′-hydroxyl by phosphoseryl- and pyrrolysyl-tRNA synthetases

Class I and II aminoacyl-tRNA synthetases (AARSs) attach amino acids to the 2′- and 3′-OH of the tRNA terminal adenosine, respectively. One exception is phenylalanyl-tRNA synthetase (PheRS), which belongs to Class II but attaches phenylalanine to the 2′-OH. Here we show that two Class II AARSs, O-phosphoseryl- (SepRS) and pyrrolysyl-tRNA (PylRS) synthetases, aminoacylate the 2′- and 3′-OH, respectively. Structure-based-phylogenetic analysis reveals that SepRS is more closely related to PheRS than PylRS, suggesting that the idiosyncratic feature of 2′-OH acylation evolved after the split between PheRS and PylRS. Our work completes the understanding of tRNA aminoacylation positions for the 22 natural AARSs.