Nuclear hormone receptor that can act as a repressor or activator of transcription. High affinity receptor for thyroid hormones, including triiodothyronine and thyroxine. Binds DNA as a dimer; homodimer and heterodimer with RXRB. Interacts with NCOA3 and NCOA6 coactivators, leading to a strong increase of transcription of target genes. Probably interacts with SFPQ. Interacts with C1D. Interacts with AKAP13. Interacts with TP53INP2. Interacts with PER2 (By similarity). Interacts with TACC1. The interaction with isoform alpha-1, but not alpha-2, is decreased in the presence of thyroid hormone T3 (By similarity). Composed of three domains: a modulating N-terminal domain, a DNA-binding domain and a C-terminal ligand-binding domain. Does not bind thyroid hormone T3. Belongs to the nuclear hormone receptor family. NR1 subfamily.