Acts as a E3 ubiquitin ligase catalyzing the covalent attachment of ubiquitin moieties onto substrate proteins (PubMed:29507230). Triggers apoptosis in response to prolonged ER stress by mediating the polyubiquitination and subsequent proteasomal degradation of BCL2L1 (PubMed:29507230). May collaborate with FATE1 to restrain BIK protein levels thus regulating apoptotic signaling (PubMed:26567849). 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. Protein modification; protein ubiquitination. Interacts with FATE1 (PubMed:26567849). Interacts with SEC16A (By similarity). Interacts with BCL2L1 (PubMed:29507230). Kidney and testis. Up-regulated by ER stress in an ERN1-dependent manner. Autoubiquitinated (in vitro).