Thyroid receptor interacting protein 1 (TRIP1) was originally identified as a protein that interacts with the thyroid receptor and is homologous to the yeast SUG1 protein, a transcriptional coactivator. It was later identified as an ATPase subunit of the 26S proteasome, a multicatalytic proteinase complex, and has also been shown to associate with nuclear receptors and transcription factors. TRIP1/SUG1 may function to regulate transcription factor abundance by targeting them for proteasome degradation.