The　anaphase-promoting　complex　(APC)　is　a　ubiquitin　ligase　responsible　for　promoting　the　degradation　of　many　cell　cycle　regulators.　One　of　the　activators　and　substrate-binding　proteins　for　the　APC　is　Cdc20.　It　has　been　shown　previously　that　Cdc20　can　promote　its　own　degradation　by　the　APC　in　normal　cycling　cells　mainly　through　a　cis-degradation　mode　(i.e.　via　an　intramolecular　mechanism).　However,　how　Cdc20　is　degraded　during　the　spindle　assembly　checkpoint　(SAC)　is　still　not　fully　clear.　In　this　study,　we　used　a　dual-Cdc20　system　to　investigate　this　issue　and　found　that　the　cis-degradation　mode　is　also　the　major　pathway　responsible　for　Cdc20　degradation　during　the　SAC.　In　addition,　we　found　that　there　is　an　inverse　relationship　between　APC(cdc20)　activity　and　the　transcriptional　activity　of　the　CDC20　promoter,　which　likely　occurs　through　feedback　regulation　by　APC(cdc20)　substrates,　such　as　the　cyclins　C1b2　and　C1b5.　These　findings　contribute　to　our　understanding　of　how　the　inhibition　of　APC(cdc20)　activity　and　enhanced　Cdc20　degradation　are　required　for　proper　spindle　checkpoint　arrest.　(C)　2017　Elsevier　Inc.　All　rights　reserved.