ABSTRACT
Thyrotropin is a member of a family of pituitary and placental heterodimeric glycoproteins containing a common alpha and unique beta subunit. The genes encoding the common α and Thyroid-stimulating hormone (TSH)-ß subunits are present as single copies and in humans are located on chromosomes 6 and 1, respectively. The human TSH-ß subunit gene consists of a 5’ untranslated exon and two coding exons. The three exons are separated by two introns of 3.9 and 0.41 kilobase pairs, respectively. The human TSH-ß subunit gene differs from that of rat and mouse TSH-ß in several respects. Thyrotropin-releasing hormone is the major positive regulator of TSH-ß subunit gene expression and acts through a guanyl nucleotide binding protein to activate phospholipase C. A model of TSH biosynthesis was proposed by F. E. Wondisford et al. The thyrotrophs secrete intact TSH and excess free α subunits. Thus, excess α subunits are present in the rough endoplasmic reticulum (RER).
