Live imaging of mRNA using RNA-stabilized fluorogenic proteins

Fluorogenic RNA aptamers bind and activate the fluorescence of otherwise nonfluorescent dyes. However, fluorogenic aptamers are limited by the small number of fluorogenic dyes suitable for use in live cells. In this communication, fluorogenic proteins whose fluorescence is activated by RNA aptamers are described. Fluorogenic proteins are highly unstable until they bind RNA aptamers inserted into messenger RNAs, resulting in fluorescent RNA–protein complexes that enable live imaging of mRNA in living cells. Pepper, an RNA aptamer that prevents degradation of degron-tagged fluorescent proteins, enables fully genetically encoded fluorescence imaging of mRNA in living cells.