Figure 3. Mechanism of TH action via its nuclear receptor. TH is transported across plasma membrane and likely diffuses through nuclear membrane to bind to its receptor. The TH receptor (open circle) is localized almost exclusively in the nucleus where it associated with DNA as a homodimer or as a heterodimer with RXR (stippled box). The hormone-activated receptor binds to TH response elements (TREs) to alter rates of gene transcription and consequently levels of mRNA.