The thyroid hormone (T3) receptors (TRs) are hormone-dependent transcription factors that regulate expression of a variety of specific target genes. TRIP13 specifically interacts with the ligand binding domain of the TRs. It is a member of Trips (TR-interacting proteins) family. Nearly all of the Trips also show similar ligand-dependent interaction with the retinoid X receptor (RXR), but none interact with the glucocorticoid receptor under any conditions. Trips predict specific functional roles: one is an apparent human homolog of a yeast transcriptional coactivator, one is a new member of a class of nonhistone chromosomal proteins, and one contains a conserved domain associated with ubiquitination of specific target proteins.