It was hypothesized that the human PRRC2B protein (Uniprot accession Q5JSZ5) interacts with its RNA binding targets via methylated arginines. The protein contains at least two RG rich motifs (residues 1061-1080, and 1104-1124), in which the arginines are hypothesized to be methylated. The goal of the experiment was to identify such methylated PRRC2B arginines. To get a wide coverage of the RG rich domains, an immuno-precipitation experiment was performed, followed by digestion with chymotrypsin and LC-MS/MS analysis.