E3 ubiquitin-protein ligase (PubMed:22529100). May facilitate apoptosis by inhibiting APC/C-Cdh1-mediated poly-ubiquitination and subsequent proteasome-mediated degradation of the pro-apoptotic protein MOAP1 (PubMed:19100260, PubMed:22529100). Regulates the G1/S transition of the cell cycle and DNA damage-induced G2 arrest by stabilizing CDKN1A/p21 (PubMed:23213251). Positively regulates CDKN1A/p21 stability by competing with DTL for CDKN1A/p21 binding, therefore disrupting DCX(DTL) E3 ubiquitin ligase complex-mediated CDKN1A/p21 ubiquitination and degradation (PubMed:23213251). Regulates the G1/S transition of the cell cycle and DNA damage-induced G2 arrest by stabilizing CDKN1A/p21 (PubMed:23213251). Positively regulates CDKN1A/p21 stability by competing with DTL for CDKN1A/p21 binding, therefore disrupting DCX(DTL) E3 ubiquitin ligase complex-mediated CDKN1A/p21 ubiquitination and degradation (PubMed:23213251). Negatively regulates the canonical NF-kappa-B signaling pathway via stabilization of CACTIN in an ubiquitination-independent manner (PubMed:26363554). 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. Isoform 1 interacts with MOAP1 (PubMed:19100260). Isoform 1 and isoform 2 interact with CDKN1A (PubMed:23213251). Isoform 2 interacts (via domain B box-type) with CACTIN (PubMed:26363554). Found predominantly in the cytosol. Partial shift from the cytosol to the mitochondria when colocalized with MOAP1. Colocalizes with CDKN1A in the nucleus. Colocalizes with CDKN1A in the nucleus. Ubiquitous; highly expressed in brain, heart, kidney, liver, skeletal muscle, spleen and testis. Autoubiquitinated. Belongs to the TRIM/RBCC family.