The aminoacyl-tRNA synthetases (AARSS) in an organism have evolved to catalyze aminoacylation of their cognate tRNAs
1
either at the 3’- OH or 2' - OH positions of the adenosine at the CCA end.
2
only at the 3’-OH position of the adenosine at the CCA end.
3
only at the 2’-OH position of the adenosine at the CCA end.
4
only at the C1' position of the adenosine at the CCA end.