library_construction_protocol: After SDS-PAGE gel electrophorylation and membrane transfer, we excised the areas from ~55 kDa to ~130 kDa (PTBP1 eCLIP) and from ~65 kDa to ~140 kDa (IGF2BP2 eCLIP), and then treated them with proteinase K (P8107S, New England Biolabs) to release RNA. Reverse transcription, DNA adapter ligation, PCR amplification were performed to construct the DNA libraries. The DNA libraries were purifed by 3% low melting temp agarose gels (50070, Lonza), cutting gel slices 175~350 bp, and were eluted by Qiagen MinElute gel extraction kit as previously described. All eCLIP experiments were performed twice.