Figure 2. TH receptor isoforms. The TH receptors (TR) β and α are expressed from separate genes. Each TR gene can be expressed as distinct isoforms, reflecting the use of alternate promoters and exons. The central zinc finger DNA-binding region is indicated and unique domains are shown by distinct patterns of shading. The TRβ-2 isoform, which is expressed predominantly in the pituitary and hypothalamus, contains a unique amino-terminus. The TRα-2 isoform contains unique carboxy-terminal sequences that eliminate hormone binding. The DNA- and T3-binding properties and transcriptional activity of the various isoforms are shown at the right.