RING-finger E3 ubiquitin ligase required to prevent cellular apoptosis in infected cells. Ubiquitinates and subsequently targets host pro-apoptotic cellular proteins such as HID for degradation by the proteasome. 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. Auto-ubiquitinated. Belongs to the IAP family.