Photo-cross-linking and high-resolution mass spectrometry for assignment of RNA-binding sites in RNA-binding proteins

RNA-protein complexes play pivotal roles in many central biological processes. Although methods based on high-throughput sequencing have advanced our ability to identify the specific RNAs bound by a particular protein, there is a need for precise and systematic ways to identify RNA interaction sites on proteins. We have developed an experimental and computational workflow combining photo-induced cross-linking, high-resolution mass spectrometry and automated analysis of the resulting mass spectra for the identification of cross-linked peptides, cross-linking sites and the cross-linked RNA oligonucleotide moieties of such RNA-binding proteins. The workflow can be applied to any RNA-protein complex of interest or to whole proteomes. We applied the approach to human and yeast mRNA-protein complexes in vitro and in vivo, demonstrating its powerful utility by identifying 257 cross-linking sites on 124 distinct RNA-binding proteins. The open-source software pipeline developed for this purpose, RNPxl, is available as part of the OpenMS project.