Thyroid hormones
The thyroid hormones function via a well-studied set of nuclear receptors, termed the thyroid hormone receptors. These receptors, together with corepressor molecules, bind DNA regions called thyroid hormone response elements (TREs) near genes. This receptor-corepressor-DNA complex can block gene transcription. Triiodothyronine (T3), which is the active form of thyroxine(T4), goes on to bind to receptors. The deiodinase catalyzed reaction removes an iodine atom from the 5' position of the outer aromatic ring of Thyroxine's (T4) structure. When triiodothyronine (T3) binds a receptor, it induces a conformational change in the receptor, displacing the corepressor from the complex. This leads to recruitment of coactivator proteins and RNA polymerase, activating transcription of the gene.
Wolff–Chaikoff effect
The Wolff–Chaikoff effect is known as an autoregulatory phenomenon that inhibits organification in the thyroid gland, the formation of thyroid hormones inside the thyroid follicle, and the release of thyroid hormones into the bloodstream. This becomes evident secondary to elevated levels of circulating iodide. The Wolff–Chaikoff effect is an effective means of rejecting a large quantity of imbibed iodide, and therefore preventing the thyroid from synthesizing large quantities of thyroid hormone. Excess iodide transiently inhibits thyroid iodide organification. In individuals with a normal thyroid, the gland eventually escapes from this inhibitory effect and iodide organification resumes; however, in patients with underlying autoimmune thyroid disease, the suppressive action of high iodide may persist. 
The Wolff–Chaikoff effect lasts several days (around 10 days), after which it is followed by an "escape phenomenon," which is described by resumption of normal organification of iodine and normal thyroid peroxidase function. "Escape phenomenon" is believed to occur because of decreased inorganic iodine concentration inside the thyroid follicle below a critical threshold secondary to down-regulation of sodium-iodide symporter (NIS) on the basolateral membrane of the thyroid follicular cell.