Xenopsin: The Neurotensin-Like Octapeptide from Xenopus Skin at the Carboxyl Terminus of Its Precursor

We have synthesized two oligodeoxyribonucleotide mixtures that contain sequences complementary to different parts of the hypothetical mRNA sequence of xenopsin, a biologically active octapeptide found in skin extracts from Xenopus laevis. The two primer pools were independently used to initiate reverse transcription on skin poly(A)+RNA and the resulting cDNAs were then used to screen in parallel a cDNA library prepared from skin poly(A)+RNA. One of the clones that hybridized with both probes was subjected to sequence analysis. It contains a nearly full-length DNA copy of a mRNA of ≈ 490 nucleotides that encodes a xenopsin precursor protein. The deduced precursor is 80 amino acids long, exhibits a putative signal sequence at the NH2terminus, and contains the biologically active peptide at the COOH terminus. The region corresponding to the NH2-terminal portion of the xenopsin precursor shows a striking nucleotide and amino acid sequence homology with the precursor of PYLa, another recently described peptide from Xenopus skin.