APC3 (anaphase-promoting complex subunit 3) is a member of the E3 enzyme family. This protein contains TPR repeats and has a molecular weight of approximately 95 kD. The APC3 protein is located at the spindle poles, the spindle microtubules, kinetochores and chromosome arms. This protein is required for core stability and functions as a multisubunit cell cycle ubiquitin ligase, and a regulator of sister chromatid separation by degrading securins. In addition, this protein functions in ubiquitin-dependent cyclin catabolism, metaphase/anaphase transition, and spindle elongation. The APC3 protein comprises one subunit of the anaphase promoting complex including APC1-8, and other probable complex proteins APC9-11, Cdc26, Mnd2, Swm1. The APC complex is inactivated by protein kinase A and is activated by CDC20 and Cdh1. The APC3 protein interacts with Rb, Mad2, p55CDC, BUBR1, as well as the APC complex proteins noted above. The APC3 protein can be modified by phosphorylation by cdk1-cyclin B. The Poly6109 antibody has been shown to be useful for Western blotting of the human APC3 protein.