PARIS: Psoralen Analysis of RNA Interactions and Structures with High Throughput and Resolution.

RNA has the intrinsic propensity to form base pairs, leading to complex intramolecular and intermolecular helices. Direct measurement of base pairing interactions in living cells is critical to solving transcriptome structure and interactions, and investigating their functions (Lu and Chang, Curr Opin Struct Biol 36:142-148, 2016). Toward this goal, we developed an experimental method, PARIS (Psoralen Analysis of RNA Interactions and Structures), to directly determine transcriptome-wide base pairing interactions (Lu et al., Cell 165(5):1267-1279, 2016). PARIS combines four critical steps, in vivo cross-linking, 2D gel purification, proximity ligation, and high-throughput sequencing to achieve high-throughput and near-base pair resolution determination of the RNA structurome and interactome in living cells. In this chapter, we aim to provide a comprehensive discussion on the principles behind the experimental and computational strategies, and a step-by-step description of the experiment and analysis.