A sample CLIP experiment for hnRNP A1, a 36-kDa RNA-binding protein. The strong cross-linked bands at 42 kDa in lanes 3 and 4 are dependent on UV treatment and antibody in the immunoprecipitation as well as a proper level of ribonuclease activity. The region shown in the autoradiogram (fourth lane from the left, dashed square) should be excised from the gel and treated to continue isolation of the RNA. (Courtesy of Jeremy Sanford, University of California, Santa Cruz.)