(B) The two Cdc20-binding domains of BubR1 interact with AAA-Cdc20 differentially. Flag-tagged BubR1 (1–477) or BubR1 (490–679) was transiently expressed in iMEFs from which Cdc20 was immunoprecipitated. The immune complexes were analyzed with Western blotting. Note that the same mouse monoclonal anti-Cdc20 antibodies were used for immunoprecipitation (IP) and Western blotting.