Measuring the activity and structure of functional RNAs inside compartments formed by liquid-liquid phase separation.

Liquid-liquid phase separation (LLPS) has been known to drive formation of biomolecular compartments, which can encapsulate RNA and proteins among other cosolutes. Such compartments, which lack a lipid membrane, have been implicated in origins of life scenarios as they can easily uptake and concentrate biomolecules, similar to intracellular condensates. Indeed, chemical interactions that drive LLPS in vitro have also been shown to lead to similar sub-cellular compartments in vivo. Here we describe methods to prepare compartments formed by complex coacervates, which are driven by LLPS of oppositely-charged polyions, and to probe the structures and functions of RNAs in them. These methods can be adapted to study RNA biochemistry in compartments formed by diverse artificial and biological macromolecules.