Nuclear hormone receptor that can act as a repressor or activator of transcription. High affinity receptor for thyroid hormones, including triiodothyronine and thyroxine. Highest level of expression in erythrocytes. Also expressed in liver, tail, eye, muscle and skin. Expression is low at stage XII of tadpole development, greatly increases by stage XIX, decreases thereafter and is relatively low by stage XXIV, when metamorphosis is almost complete. By thyroid hormone. 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.