Mediates E3-dependent ubiquitination and proteasomal degradation of target proteins, including p53/TP53, P73, HDAC1 and CDKN1B. Preferentially acts on tetrameric p53/TP53. Monoubiquitinates the translesion DNA polymerase POLH. Contributes to the regulation of the cell cycle progression. Increases AR transcription factor activity. 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. Monomer and homodimer. Interacts with AR, p53/TP53, MDM2, HDAC1, KAT5, PLAG1, PLAGL2, CDKN1B, COPE, UBE2D2 and GORAB/NTKLBP1. Up-regulated during the S phase of the cell cycle. Expressed at low levels during G phase. Subject to ubiquitination and proteasomal degradation. Interaction with PLAGL2 or KAT5 enhances protein stability. No ubiquitin protein ligase activity. Down-regulated in hepatocellular carcinoma. Gene prediction based on partial mRNA data. Extended N-terminus.