The GnRH I gene comprises four exons separated by three introns and is located on chromosome 8p11.2-p21.^[56,57] The first exon of the gene is untranslated and is composed of 61 base pairs in mRNA expressed in the hypothalamus. The second exon encodes the signal sequence, the GnRH decapeptide, and the initial 11 residues of the GnRH-associated peptide (GAP). The third exon contains the next 32 GAP residues, and the fourth exon encodes the remaining 13 GAP residues, the translation termination codon, and the entire 160-base pair (bp) 3′-untranslated region (UTR).^[56,58]

The GnRH I mRNA transcript encodes a precursor protein of 92 amino acids.^[4,58] The initial 23 amino acids form a signal sequence characteristic of a secretory protein. Cleavage of the signal peptide generates an N-terminal glutamine residue, which undergoes cyclization to pyroglutamic acid. The GnRH decapeptide is followed by the GKR (Gly-Lys-Arg) sequence and the 56 …