TRIP12 (thyroid hormone receptor interactor 12) is an ATP-dependent multisubunit protein that activates the proteolytic activities of the multifunctional proteinase (20S proteasome) of the 26S complex. TRP12 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). TRP12 was originally identified as a factor that interacts with the thyroid hormone receptor. It was later found to also interact with AAP-BP1, a component of the NEDD8 –activating enzyme, and function as an E3 ubiquitin ligase for AAP-BP1.