Apc11 is one of the subunits of the anaphase-promoting complex or cyclosome. The APC subunits are cullin family proteins with ubiquitin ligase activity. Polyubiquitination marks proteins for degradation by the 26S proteasome and is carried out by a cascade of enzymes that includes ubiquitin-activating enzymes (E1s), ubiquitin-conjugating enzymes (E2s), and ubiquitin ligases (E3s). Apc11 acts as an E3 enzyme and is responsible for recruiting E2s to the APC and for mediating the subsequent transfer of ubiquitin to APC substrates in vivo. In Saccharomyces cerevisiae this RING-H2 finger protein defines the minimal ubiquitin ligase activity of the APC, and the integrity of the RING-H2 finger is essential for budding yeast cell viability.