function:Component of PA700, an ATP-dependent multisubunit protein that activates the proteolytic activities of the multifunctional proteinase (20S proteasome) of the 26S complex. Specifically interacts with the ligand binding domain of the thyroid hormone receptor (in a thyroid hormone T3-independent manner) and with retinoid X receptor (RXR). Could be E3 ubiquitin-protein ligase which accepts ubiquitin from an E2 ubiquitin-conjugating enzyme in the form of a thioester and then directly transfers the ubiquitin to targeted substrates.,miscellaneous:A cysteine residue is required for ubiquitin-thioester formation.,pathway:Protein modification; protein ubiquitination.,PTM:Phosphorylated upon DNA damage, probably by ATM or ATR.,similarity:Belongs to the UPL family. K-HECT subfamily.,similarity:Contains 1 HECT (E6AP-type E3 ubiquitin-protein ligase) domain.,similarity:Contains 1 WWE domain.,subunit:PA700 is composed of at least 16 distinct peptides ranging from 20-112 kDa.,