Aminoacyl tRNA synthetase (aaRS) catalyzes the esterification of a specific amino acid to its cognate tRNA to form an aminoacyl-tRNA. The amino acid is transferred by the ribosome from the aminoacylated-tRNA onto a growing polypeptide chain. Class I of aaRS is a monomer or dimer, it has 2 highly conserved sequence motifs and it aminoacylates at the 2’-OH of an adenosine nucleotide. Class II of aaRS is a dimer or tetramer, it has 3 highly conserved sequence motifs and it aminoacylates at the 3’-OH of an adenosine nucleotide. CP1 domain of RS edits a mischarged aa-tRNA. Some of the crystal structures are complexes of the RS with their reactant analog: amino acid-sulfamoyl adenine (aa-SA).[1] For pyrrolysyl-RS details see Pyrrolysyl-tRNA synthetase.
