Together with the cullin protein ANAPC2, constitutes the catalytic component of the anaphase promoting complex/cyclosome (APC/C), a cell cycle-regulated E3 ubiquitin ligase that controls progression through mitosis and the G1 phase of the cell cycle. The APC/C complex acts by mediating ubiquitination and subsequent degradation of target proteins: it mainly mediates the formation of 'Lys-11'-linked polyubiquitin chains and, to a lower extent, the formation of 'Lys-48'- and 'Lys-63'-linked polyubiquitin chains. May recruit the E2 ubiquitin-conjugating enzymes to the complex. Protein modification; protein ubiquitination. The mammalian APC/C is composed at least of 14 distinct subunits ANAPC1, ANAPC2, CDC27/APC3, ANAPC4, ANAPC5, CDC16/APC6, ANAPC7, CDC23/APC8, ANAPC10, ANAPC11, CDC26/APC12, ANAPC13, ANAPC15 and ANAPC16 that assemble into a complex of at least 19 chains with a combined molecular mass of around 1.2 MDa; APC/C interacts with FZR1 and FBXO5 (PubMed:26083744, PubMed:10922056, PubMed:25043029). Interacts with the cullin domain of ANAPC2 (PubMed:11739784). Interacts with UBE2D2 (PubMed:11739784). Expressed at high levels in skeletal muscle and heart; in moderate levels in brain, kidney, and liver; and at low levels in colon, thymus, spleen, small intestine, placenta, lung and peripheral blood leukocyte. The RING-type zinc finger domain coordinates an additional third zinc ion. Auto-ubiquitinated. Belongs to the RING-box family.