APEX-seq Captures the Protein-RNA Interaction Patterns of DDX3X and DDX3Y

Although stress granules (SGs) are composed of a stable core structure, they are surrounded by a dynamic shell with assembly, disassembly, and transitions of proteins and RNA between the core and shell. Different SGs have distinct proteins and RNA constituents, which raises the possibility that different SGs might perform different biological functions. The RNA compositions of DDX3X- or DDX3Y-positive SGs are not known, nor is it known what differential effects DDX3X or DDX3Y may exert on these RNA components. To understand the biological function and the compositional differences between DDX3X- or DDX3Y-positive SGs, we first determined the RNA constituents in these SGs using an adapted Ascorbate-peroxidase (APEX)-based proximity labeling method. APEX converts exogenously supplied biotin-phenol (BP) to biotin-phenoxyl radicals, which in turn covalently labels protein and RNA in nanometers. APEX-mediated biotinylation has been widely used in studies of protein-protein interactions and recently in studying protein-RNA interactions. Here, we applied the APEX-mediated biotinylation in DDX3X and DDX3Y SGs to dissect their different RNA composition. RNA-seq after streptavidin beads pulldown of biotin-labeled RNA for APEX2-EGFP, APEX2-DDX3X, and APEX2-DDX3Y transient expression HeLa cells with arsenite treatment.