Nanoscale Imaging of RNA-Protein Interactions with a Photoactivatable Trimolecular Fluorescence Complementation System.

Imaging RNA-protein interaction in the cellular space with single molecule sensitivity is attractive for studying gene expression and regulation, but remains a challenge. In this study, we reported a photoactivatable trimolecular fluorescence complementation (TriFC) system based on fluorescent protein, mIrisFP, to identify and visualize RNA-protein interactions in living mammalian cells. We also combined this TriFC system with photoactivated localization microscopy (PALM), named the TriFC-PALM technique, which allowed us to image the RNA-protein interactions with single molecule sensitivity. Using this TriFC-PALM technique, we identified the actin-bundling protein, FSCN1, specifically interacting with the HOX Transcript Antisense RNA (HOTAIR). The TriFC-PALM imaging acquired a higher resolution compared with the traditional method of total internal reflection (TIRF) imaging. The TriFC-PALM thus provides a useful tool for imaging and identifying the RNA-protein interactions inside cells at the nanometer scale.