HeLa nuclear extracts and RNase A were incubated with GST-PHAX and FLAG-UAP56 in the presence of ATP. The mixture was subjected to immunoprecipitation. The bound proteins were eluted with FLAG peptide. The eluate was subjected to GST pull-down. The bound proteins were treated with HRV 3C protease. Supernatants were analysed by SDS-PAGE and mass spectrometry.