E3 ubiquitin-protein ligase which accepts ubiquitin from E2 ubiquitin-conjugating enzymes UBE2L3 and UBE2L6 in the form of a thioester and then directly transfers the ubiquitin to targeted substrates such as LCMT2, thereby promoting their degradation. Induces apoptosis via a p53/TP53-dependent but caspase-independent mechanism. However, its overexpression also produces a decrease of the ubiquitin-dependent stability of BAX, a pro-apoptotic protein, ultimately leading to protection of cell death; But, it is not an anti-apoptotic protein per se. [E2 ubiquitin-conjugating enzyme]-S-ubiquitinyl-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-N(6)-ubiquitinyl-L-lysine. Protein modification; protein ubiquitination. Interacts with UBE2L3, UBE2L6 and LCMT2, as well as with BAX. Mostly cytosololic, accumulates in submitochondrial domains specifically upon apoptosis induction, in synchrony with BAX activation. Broadly expressed, with lowest levels in brain and thymus, and highest levels detectable in heart, ovary and testis. The RING-type zinc finger domain mediates binding to an E2 ubiquitin-conjugating enzyme (By similarity). The transmembrane domain is essential for translocation to the mitochondria upon induction of apoptosis. Members of the RBR family are atypical E3 ligases. They interact with the E2 conjugating enzyme UBE2L3 and function like HECT-type E3 enzymes: they bind E2s via the first RING domain, but require an obligate trans-thiolation step during the ubiquitin transfer, requiring a conserved cysteine residue in the second RING domain. Auto-ubiquitinated. Belongs to the RBR family. RNF144 subfamily. Lacks the His residue in the RING-type domain 2 that is one of the conserved features of the family.