Site-specific enzymatic introduction of a norbornene modified unnatural base into RNA and application in post-transcriptional labeling.

Inverse electron demand Diels-Alder cycloadditions have proven to be extremely useful for mild and additive-free orthogonal labeling of biomolecules, amongst others, for RNA labeling in vitro and in a cellular context. Here we present a method for site-specific introduction of an alkene modification into RNA via T7 in vitro transcription. For this, an unnatural, hydrophobic base pairing system developed by Romesberg and coworkers was modified introducing one or two norbornene moieties at predefined positions into RNA oligonucleotides in an in vitro transcription reaction. This allows post-transcriptional functionalization of these RNA molecules with tetrazine derivatives containing for instance fluorophores or biotin.