The inhibitor of apoptosis, cIAP2, functions as a ubiquitin-protein ligase and promotes in vitro monoubiquitination of caspases 3 and 7.

The inhibitor of apoptosis, cIAP2, contains a putative Ring finger motif at the C terminus. Using in vitro ubiquitination assays, we found that the Ring finger of cIAP2 alone possesses intrinsic ubiquitin ligase activity and promotes substrate-independent ubiquitination. It also promotes ubiquitination of caspases 3 and 7 but not caspase-1. The Ring fingers of c-Cbl and Apc11 failed to promote caspase-7 ubiquitination, suggesting that the Ring finger of cIAP2 itself is involved in substrate recognition.