Structure and function of the thyroid hormone receptor

Cloning of the thyroid hormone receptor and its identification as a cellular counterpart of the viral oncogene v-erbA was a major breakthrough in the study of thyroid hormone action. However, contrary to our initial expectations, many astonishing findings which have accumulated since the receptor cloning, especially the presence of two receptor types, made the elucidation of the thyroid hormone action extremely complicated. In this paper, we mainly did a phylogenic comparison of the amino acid sequence between alpha- and beta-type receptor from Xenopus laevis to humans, hoping to obtain some clue to clarify the functional differences between these receptors. There are several consistent amino acid differences between alpha- and beta-receptor through species in the DNA binding domain, one of which is non-conservative and is located in the portion supposed to be critical to the protein-protein interaction. We believe that clarification of the physiological significance of the presence of two receptor types will facilitate the study of thyroid hormone action.