TRIP4 (thyroid hormone receptor interactor 4) encodes a subunit of the tetrameric nuclear activating signal cointegrator 1 (ASC-1) complex, which associates with transcriptional coactivators, nuclear receptors and basal transcription factors to facilitate nuclear receptors-mediated transcription. This protein is localized in the nucleus and contains an E1A-type zinc finger domain, which mediates interaction with transcriptional coactivators and ligand-bound nuclear receptors, such as thyroid hormone receptor and retinoid X receptor alpha, but not glucocorticoid receptor. Mutations in TRIP4 are associated with spinal muscular atrophy with congenital bone fractures-1 (SMABF1).