Towards Covalent Fluorescent Light-Up Aptamers (coFLAPs)

The fluorogen-activating aptamer, Spinach, was a milestone in cellular RNA imaging and conceptually similar to the green fluorescent protein (GFP). Since then, more than ten FLAP systems have been developed across a broad spectral range. All of these systems differ fundamentally from GFP in that FLAPs rely on noncovalent fluorogen-RNA interactions, whereas GFP integrates its fluorophore covalently. In this article, we discuss recently developed FLAPs, including the first covalent FLAP, coPepper, as a promising new strategy to overcome current limitations in FLAP-based RNA imaging. Moreover, the bioconjugation chemistry developed for coFLAPs has immediate impact on covalent RNA labeling, RNA drug targeting, and in general, on covalent drug design.