hNRNPC iCLIP. hNRNPC iCLIP

UV-crosslinking and immunoprecipitation (CLIP) combined with high-throughput sequencing was previously used to generate transcriptome-wide binding maps of several RNA-binding proteins9-12. However, since identification of binding sites relied on the analysis of overlapping sequence clusters, distances of less than 30 nucleotides were not resolved. An additional disadvantage of CLIP is the requirement of reverse transcription to pass over residual amino acids that remain covalently attached to the RNA at the crosslink site. Primer extension assays have shown that the vast majority of cDNAs prematurely truncate immediately before the 'crosslink nucleotide'13. Here, we exploited this apparent limitation to achieve single nucleotide resolution by capturing these truncated cDNAs through the introduction of a second adapter after reverse transcription via self-circularization. In order to quantify cDNA molecules that truncate at the same nucleotide, we added a random barcode to the DNA adapter. This allowed us to discriminate between unique cDNA products and PCR duplicates . Taken together, individual-nucleotide resolution CLIP (iCLIP) enables precise mapping of protein-RNA interactions in intact cells.