High affinity receptor for triiodothyronine (T3). Binds to thyroid hormone receptor element (TRE) weakly as homodimers and monomers, but binds TRE with much higher affinity as heterodimers with retinoid X receptors. Can bind DNA as a heterodimer with either rxra or rxrg. Composed of three domains: a modulating N-terminal domain, a DNA-binding domain and a C-terminal ligand-binding domain. Belongs to the nuclear hormone receptor family. NR1 subfamily. The sequence derived in PubMed:2402492 was probably derived from a mutant gene and shows poor transcriptional activation and DNA-binding activity, but is still able to efficiently form heterodimers with retinoic acid receptors.