Characterization of the DOC1/APC10 subunit of the yeast and the human anaphase-promoting complex

The anaphase-promoting complex/cyclosome (APC) is a ubiquitin-protein ligas e whose activity is essential for progression through mitosis. The vertebra te APC is thought to be composed of 8 subunits, whereas in budding yeast se veral additional APC-associated proteins have been identified, including a 33-kDa protein called Doc1 or Apc10, Here, we show that Doc1/Apc10 is a sub unit of the yeast APC throughout the cell cycle. Mutation of Doc1/Apc10 ina ctivates the APC without destabilizing the complex, An ortholog of Doc1/Apc 10, which we call APC10, is associated with the APC in different vertebrate s, including humans and frogs. Biochemical fractionation experiments and ma ss spectrometric analysis of a component of the purified human APC show tha t APC10 is a genuine APC subunit whose cellular levels or association with the APC are not cell cycle-regulated, We have further identified an APC10 h omology region, which we propose to call the DOC domain, in several protein sequences that also contain either cullin or HECT domains. Cullins are pre sent in several ubiquitination complexes including the APC, whereas HECT do mains represent the catalytic core of a different type of ubiquitin-protein ligase, DOC domains may therefore be important for reactions catalyzed by several types of ubiquitin-protein ligases.