Leveraging advances in RNA editing, a team led by researchers from the Massachusetts Institute of Technology has developed a technique for triggering the production of specific proteins in live cells. The approach, which is detailed in Nature Biotechnology, can be used for a range of applications including tracking transcriptional states, RNA-sensing-induced cell death, cell type identification, and control of synthetic mRNA translation. The approach uses an RNA engineered to contain a guide region that binds to a target cellular RNA sequence and a region that encodes a protein of interest. When the guide RNA binds to its target, a short double-stranded RNA sequence containing an adenosine-to-cytosine mismatch is generated. This mismatch recruits a naturally occurring family of RNA-editing proteins called adenosine deaminases acting on RNA (ADARs), which inactivate a cellular stop signal blocking production of the desired protein, allowing for its translation. Importantly, the protein of interest is only produced after the guide RNA binds to its target and triggers the ADARs. The researchers show that the engineered RNAs, dubbed RADARS, can produce a range of proteins — including luciferases, fluorescent proteins, recombinases, and apoptosis-inducing caspases — and can distinguish between different cell types including kidney, uterine, and live cells. RADARS also measured gene expression over a large dynamic range, demonstrating their utility as sensors. "Overall, RADARS forms the basis of a reprogrammable biological sensor platform with many applications for biomedical research, diagnostics, and therapeutics," they write.