RaPure Total RNA kit (Magen) was used to isolate total RNA according to the manufacturer's instructions. cDNA was synthesized using reverse transcriptase (Promega). CUL4A, CUL4B, DDB1, MMS22L and ESCO2 plasmids for transient expression were generated previously (22 (link)). GSK3A and GSK3B full-length genes were generated by PCR and were inserted into the pRK5-FLAG vector. All genes were sub-cloned into other vectors when necessary. See Supplementary Table S2 for details of plasmids used in this study, Supplementary Table S3 for plasmids generated in this study, and Supplementary Table S4 for primers used in this study.