Apoptotic regulator capable of exerting proapoptotic and anti-apoptotic activities and plays crucial roles in apoptosis, cell proliferation, and cell cycle control. Its anti-apoptotic activity is mediated through the inhibition of CASP3, CASP7 and CASP9, as well as by its E3 ubiquitin-protein ligase activity. As it is a weak caspase inhibitor, its anti-apoptotic activity is thought to be due to its ability to ubiquitinate DIABLO/SMAC targeting it for degradation thereby promoting cell survival. May contribute to caspase inhibition, by blocking the ability of DIABLO/SMAC to disrupt XIAP/BIRC4-caspase interactions. Protects against apoptosis induced by TNF or by chemical agents such as adriamycin, etoposide or staurosporine. Suppression of apoptosis is mediated by activation of MAPK8/JNK1, and possibly also of MAPK9/JNK2. This activation depends on TAB1 and MAP3K7/TAK1. In vitro, inhibits CASP3 and proteolytic activation of pro-CASP9. 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. Binds to caspase-9. Interaction with DIABLO/SMAC via the BIR domain disrupts binding to caspase-9 and apoptotic suppressor activity. Interacts with TAB1. In vitro, interacts with caspase-3 and caspase-7 via its BIR domain. Nuclear, and in a filamentous pattern throughout the cytoplasm. Full-length livin is detected exclusively cytoplasm, whereas the truncated form (tLivin) is found in the peri-nuclear region with marked localization to the Golgi apparatus; the accumulation of tLivin in the nucleus shows positive correlation with the increase in apoptosis. The RING domain is essential for autoubiquitination. Autoubiquitinated and undergoes proteasome-mediated degradation. The truncated protein (tLivin) not only loses its anti-apoptotic effect but also acquires a pro-apoptotic effect. Belongs to the IAP family. Truncated N-terminus. Truncated N-terminus.