abbr.: APC; a protein complex that initiates the separation of sister chromatids and the onset of anaphase during cell division. It is a 20S particle that contains Cdc16, Cdc23, and Cdc 27 and acts as an E3 enzyme (ubiquitin — protein ligase) in the ubiquitination of cyclin B. See cdcgene, cyclin, ubiquitin — protein ligase.