RNA cleavage can occur either: (i) by a transesterification mechanism that yields 2’,3’-cyclic-PO 4 and 5’-OH ends; or (ii) via a hydrolytic mechanism that leaves 3’-OH and 5’-PO 4 ends. RNA repair ...

This step occurs by transesterification ... Nonetheless, because nearly all eukaryotes have introns and share mechanisms of RNA splicing, splicing itself must be quite ancient.