Biosynthesis of peptides in the skin of Xenopus laevis: isolation of novel peptides predicted from the sequence of cloned cDNAs.

From skin of Xenopus laevis, a few peptides have been isolated which are identical or homologous to gastrointestinal hormones and/or neurotransmitters of mammalian origin. We have studied the biosynthesis of these peptides using recombinant DNA techniques. From cDNA librariers constructed from skin mRNA, clones with inserts coding for the precursors of caerulein, thyrotropin releasing hormone and a new peptide termed PGLa have been isolated and sequenced. In the case of caerulein, a small family of precursors containing one, three or four copies of the end product have been detected. The caerulein sequences are separated by homologous sequences which potentially could give rise to additional constituents of skin secretion. Three such peptides have been detected which are presumably liberated from caerulein precursors by cleavage at single arginine residues.