MS2-TRIBE Evaluates Both Protein-RNA Interactions and Nuclear Organization of Transcription by RNA Editing

Both UV-cross-linking and immunoprecipitation (CLIP) and RNA editing (TRIBE) can identify the targets of RNA-binding proteins. To evaluate false-positives of CLIP and TRIBE, endogenous beta-actin mRNA was tagged with MS2 stem loops, making it the only bona fide target mRNA for the MS2 capsid protein (MCP). CLIP and TRIBE detected beta-actin, albeit with false-positives. False-positive CLIP signals were attrib-uted to nonspecific antibody interactions. In contrast, putative false-positive TRIBE targets were genes spatially proximal to the 0-actin gene. MCP-ADAR edited nearby nascent transcripts consistent with interchromosomal contacts observed in Hi-C. The identification of nascent contacts implies RNA regulatory proteins (e.g., splicing factors) associated with multiple nascent transcripts, forming domains of post-transcriptional activity. Repeating these results with an integrated inducible MS2 reporter indicated that MS2-TRIBE can be applied to a broad array of cells and transcripts to study spatial organization and nuclear RNA regulation.