May have a role during the programmed cell death of hematopoietic cells (By similarity). Acts as an E3 ubiquitin-protein ligase. 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. Ubiquitously expressed. Highly expressed in leukocytes. Not expressed in erythroblasts. In vivo measurements suggest this protein is glycosylated (PubMed:19159218). In contrast, in vitro experiments failed to detect glycosylation (PubMed:16549277). Extended N-terminus.