| Studies in our laboratory and those of other investigators had led us to believe in the existence of only a single thyroid hormone receptor. Our confidence in this conclusion was shaken with the back-to-back reports in the Christmas 1986 issue of Nature which showed that the two laboratories. The Vennstrom's laboratory in Heidelberg described a receptor gene located on human chromosome 17, which was subsequently designated TRa. Evans' laboratory in San Diego reported a receptor gene situated on human chromosome 3, which was later designated TRb. By alternative splicing each of the transcripts yields two products, defined as TRb1 and TRb2 and TRa1 and TRa2. Each of these 4 isoforms showed essentially the same spectrum of analog affinity with the exception of TRa2 which did not bind T3 at all. The T3 binding region is located toward carboxyl region of the receptor whereas the DNA binding is situated more closely to the amino terminus. |
