E3 ubiquitin-protein ligase (By similarity). May facilitate apoptosis by inhibiting APC/C-Cdh1-mediated poly-ubiquitination and subsequent proteasome-mediated degradation of the pro-apoptotic protein MOAP1 (By similarity). Regulates the G1/S transition of the cell cycle and DNA damage-induced G2 arrest by stabilizing CDKN1A/p21 (By similarity). 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 (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 MOAP1 (By similarity). Interacts with CDKN1A (By similarity). Found predominantly in the cytosol. Partial shift from the cytosol to the mitochondria when colocalized with MOAP1. Colocalizes with CDKN1A in the nucleus. Autoubiquitinated. Belongs to the TRIM/RBCC family.