Abstract
Live labelling of active transcription sites is critical to our understanding of transcriptional dynamics. In the most widely used method, RNA sequence MS2 repeats are added to the transcript of interest, on which fluorescently tagged Major Coat Protein binds, and labels transcription sites and transcripts. Here we describe another strategy, using the Argonaute protein NRDE-3, repurposed as an RNA-programmable RNA binding protein. We label active transcription sites in C. elegans embryos and larvae, without editing the gene of interest. NRDE-3 is programmed by feeding nematodes with double-stranded RNA matching the target gene. This method does not require genome editing and is inexpensive and fast to apply to many different genes. Graphical abstract.