Cloning of cDNAs for the Pituitary Glycoprotein Hormone Alpha Subunit Precursor Molecules in Three Amphibian Species,Bufo japonicus,Rana catesbeiana,andCynops pyrrhogaster

Abstract

We have isolated cDNA clones encoding molecules of putative glycoprotein hormone alpha subunit precursors from their pituitary cDNA libraries for a toad, bullfrog and newt. The insert of the isolated toad cDNA was 562 bp long containing the 5′-untranlated, coding and 3′-untranslated regions of 38, 363 and 161 bp, respectively. The insert of the bullfrog cDNA was 604 bp long containing the 5′-untranslated, coding and 3′-untranslated regions of 70, 366, and 168 bp, respectively. In the newt, a composite cDNA sequence was estimated from four isolated partial clones. It was 694 bp long and contained the 5′-untranslated region of 89 bp, coding region of 366 bp, and 3′-untranslated region of 91 bp or longer. Amino acid sequences deduced from coding regions of the isolated clones showed that the signal peptides consist of 24 residues and the mature proteins of 96 (toad) or 97 residues (bullfrog and newt). In all three species, an insertion of an amino acid residue was found between residues 26 and 27 of the alpha subunit molecule sequence of all other vertebrate species studied. Interestingly, the percentage identities of the entire amino acid sequence between amphibian and mammalian (or avian) alpha subunits are lower than those between lungfish and mammalian (or avian) alpha subunits. This suggests that amino acid substitutions have occurred more frequently during the course of evolution in the alpha subunit molecule of amphibians than in that of other tetrapod vertebrates, although the biological significance of this is not known.