The APC complex was purified from insect cells and an in vitro phosphorylation purified WT cyclin B1 or pocket mutant cyclin B1 was performed. Phosphorylation sites were detected by mass spectrometry (in vitro data). WT cyclin B1 and mutant cyclin B1 was transfected in cells and the APC complex immunoprecipitated with an anti-APC3 antibody and binders identified by MS