TABLE 3.

Proposed subgroups of class II aaRSs

¹ Aminoacylation site (2′ or 3′ OH of the terminal ribose of the cognate tRNA).

² Number of residues in motif two that do not agree with the canonical sequence.

³ Although this proposed classification is based solely on the structural and sequence features of the catalytic core of class IIaaRSs, there are some characteristics that are shared among its members.

⁴ Editing carried out after the first step of the reaction against standard amino acids.

⁵ ABCD is anticodon binding domain.

⁶ PylRS can be either subclass IIc according to the structural analysis or subclass IIb according to the sequence analysis. It is placed in the frontier in this table because of the aminoacylation site properties of PheRS and SepRS, which are different from PylRS.

⁷ These domains have limited similarity between each other (Dali Z-score 2.6, r.m.s.d. 4.5 Å, % identity = 12).