Weak apoptotic suppressor. Has E3 ubiquitin-protein ligase activity. Weak inhibitor of caspase activity. S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. The BIR2 domain is required for caspase-inhibition. The C-terminal region containing the RING finger domain is required for the initial degradation step, and the final digestion of cleavage fragments. Auto-ubiquitinated, and degraded in a 2-step mechanism; a caspase-independent first step and a caspase-dependent second step. Phosphorylated via MAPK-dependent and CDK-dependent pathways during oocyte maturation. Phosphorylation does not appear to affect caspase inhibition or autoubiquitination activity. Belongs to the IAP family.