A novel reporter for helicase activity in translation uncovers DDX3X interactions.

DDX3X regulates the translation of a subset of human transcripts containing complex 5' untranslated regions (5' UTRs). In this study we developed the helicase activity reporter for translation (HART) which uses DDX3X-sensitive 5' UTRs to measure DDX3X mediated translational activity in cells. To directly measure RNA structure in DDX3X dependent mRNAs, we used SHAPE-MaP to determine the secondary structures present in DDX3X-sensitive 5' UTRs and then employed HART to investigate how sequence alterations influence DDX3X-sensitivity. Additionally, we identified residues 38-44 as potential mediators of DDX3X's interaction with the translational machinery. HART revealed that both DDX3X's association with the translational machinery as well as its helicase activity are required for its function in promoting the translation of DDX3X sensitive 5' UTRs. These findings suggest DDX3X plays a crucial role regulating translation through its interaction with the translational machinery during ribosome scanning, and establish the HART reporter as a robust, lentivirally-encoded, colorimetric measurement of DDX3X-dependent translation in cells.