Acts as a E3 ubiquitin ligase catalyzing the covalent attachment of ubiquitin moieties onto substrate proteins (PubMed:29300766). Triggers apoptosis in response to prolonged ER stress by mediating the polyubiquitination and subsequent proteasomal degradation of BCL2L1 (By similarity). May collaborate with FATE1 to restrain BIK protein levels thus regulating apoptotic signaling (By similarity). 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 (By similarity). Interacts with SEC16A (PubMed:29300766). Interacts with BCL2L1 (By similarity). Highly expressed in the kidney and testis. Autoubiquitinated (in vitro).