To confirm the SAC deficiency achieved by live cell imaging, we analysed the ability of Mad2 to interact with Cdc20, BubR1 and the APC/C under these conditions by immunoprecipitation of Mad2 and found that Bub1 RNAi resulted in reduced interaction and that this could be fully rescued by expression of Bub1 1–553 (Fig. 1e,f; Supplementary Fig. 11), revealing a role of Bub1 in efficient MCC formation. This evidence concerns the gene CDC20 and Merkel cell skin cancer.