ABSTRACT

Tissue-specific differential post-translational processing mechanisms represent a set of strategies for generating discrete subsets of polypeptide end-products from a common precursor. The isolation and characterization of POMC mRNA from the bovine pituitary, unequivocally established that corticotropin-related peptides and lipotropin-related peptides are synthesized from a common precursor. Prior to the isolation and characterization of POMC mRNA from bovine pituitary, several biochemical studies had presented evidence that corticotropin-related peptides and lipotropin-related peptides were synthesized from a common precursor. The biosynthetic intermediate, 16 K fragment contains the sequence of gamma-melanotropin. The existence of this third melanotropin sequence was only revealed following the characterization of bovine POMC mRNA. The function of this “melanotropin” is unclear. Synthetic bovine gamma-melanocyte-stimulating hormone (MSH) analogs have been tested in a variety of melanotropin bioassay systems. Alpha-MSH has been characterized in several species of nonmammalian vertebrates. The N-acetylation of alpha-MSH and beta-endorphin in the pars intermedia has a significant effect on the biological activity of these polypeptides.