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 PER2. Isoform alpha-2 and isoform alpha-1 interact with TACC1, but the interaction with alpha-1 is weaker. The interaction with isoform alpha-1, but not alpha-2, is decreased in the presence of thyroid hormone T3 (By similarity). When overexpressed found in the cytoplasm where it colocalizes with TACC1. 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.