A Chemo‐Enzymatic Approach for Site‐Specific Modification of the RNA Cap

Capped and gowned: A two-step approach can be used to site-specifically modify the 5′-cap of eukaryotic mRNAs. First, a trimethylguanosinesynthase variant recognizes the m7G cap structure and introduces bioorthogonal groups using S-adenosyl-L-methionine-based cosubstrates. Then, the enzymatically introduced reporter groups are further modified by thiol–ene or CuAAC click chemistry (see scheme).