E3 ubiquitin ligase catalyzing the covalent attachment of ubiquitin moieties onto substrate proteins (By similarity). Promotes the polyubiquitination and proteasome-dependent degradation of RELA/p65, thereby suppressing RELA-mediated NF-kappaB transactivation and negatively regulating inflammatory responses (By similarity). Plays a role in the regulation of spermiation and in male fertility (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 PDLIM2 (via LIM zinc-binding domain) (By similarity). Interacts with RELA (By similarity). Expressed in sperm, with significantly reduced expression in sperm of patients with oligoasthenoteratozoospermia (at protein level) (PubMed:28008940). Widely expressed with expression in testis, ovary, small intestine, colon, peripheral blood leukocytes, fetal liver, bone marrow, thymus, lymph node and spleen (PubMed:11597136). Partially overlaps and is antisense to the RAF1 proto-oncogene.