Visualization of the Delivery and Release of Small RNAs Using Genetic Code Expansion and Unnatural RNA-Binding Proteins

Endogenously expressed noncoding RNAs are regulators of mRNA translation and affect diverse biological pathways spanning embryogenesis to cholesterol and fatty acid metabolism. Recently, microRNAs have become an important therapeutic target with strategies that employ oligonucleotides as both mimics and inhibitors of target microRNAs, successfully altering gene expression and cellular pathways in relevant contexts. However, delivery of these exogenous effectors remains a major challenge. Here, we present a method for evaluating noncoding RNA delivery using the viral suppressor of RNA silencing (VSRS) protein p19, optimized for cellular delivery of small RNAs. Using genetic code expansion technology, p-azidophenylalanine (AzF) was incorporated into a recombinant p19 protein and used to develop a fluorescence resonance energy transfer (FRET) sensor. AzF was used to attach FRET acceptor moieties using bioorthogonal chemistry. We show that this strategy not only gives rise to FRET signals that report on small...