Arai Y, Kubokawa K, Ishii S, Joss J M
Department of Biology, School of Education, Waseda University, Tokyo, Japan.
Gen Comp Endocrinol. 1998 May;110(2):109-17. doi: 10.1006/gcen.1997.7052.
We have isolated cDNA clones encoding a putative glycoprotein hormone alpha subunit precursor molecule from a pituitary cDNA library of the Australian lungfish (Neoceratodus forsteri) by a two-step plaque hybridization technique initially using cDNA encoding the toad glycoprotein hormone alpha subunit precursor molecule as the hybridization probe. The inserts (799 bp) of two of the isolated cDNA clones contained sequences of 5' and 3' untranslated regions, including a poly(A) stretch, and the entire coding sequence of the alpha subunit precursor molecule. The deduced amino acid sequence showed that its signal peptide consists of 24 residues and its mature protein 97 residues. In the mature protein, there is an insert of one residue (Ala) just after the 9th residue. This insert is unique to the Australian lungfish among vertebrate species studied. The amino acid sequence of the mature protein shares the common, or the same-group, amino acid residues at 9 positions with tetrapod and not actinopterygian vertebrates, while only one residue is common to some teleosts and the lungfish to the exclusion of the tetrapods. The overall sequence of the mature protein of the Australian lungfish also shares more similarity with those of tetrapods (69 to 84%) than it does with teleosts (57 to 74%). These results on the relation of the alpha subunit precursor molecule between the lungfish and other vertebrates are consistent with the recent molecular phylogenetic studies suggesting a closer relationship between lungfish and tetrapods than between lungfish and teleosts. We also found that the primary structure of the lungfish alpha subunit is slightly but significantly more similar to that of homeothermic vertebrates than to that of amphibians. This may be due to specialization of the amphibian alpha subunit molecules.
我们通过两步噬菌斑杂交技术，从澳大利亚肺鱼（Neoceratodus forsteri）的垂体cDNA文库中分离出了编码假定糖蛋白激素α亚基前体分子的cDNA克隆。该技术最初使用编码蟾蜍糖蛋白激素α亚基前体分子的cDNA作为杂交探针。两个分离出的cDNA克隆的插入片段（799 bp）包含5'和3'非翻译区的序列，包括一个poly(A)序列，以及α亚基前体分子的完整编码序列。推导的氨基酸序列显示，其信号肽由24个残基组成，成熟蛋白由97个残基组成。在成熟蛋白中，第9个残基之后紧接着插入了一个残基（丙氨酸）。在已研究的脊椎动物物种中，这种插入是澳大利亚肺鱼所特有的。成熟蛋白的氨基酸序列在9个位置上与四足动物而非辐鳍鱼类共有相同或同组的氨基酸残基，而在一些硬骨鱼和肺鱼中只有一个残基相同，四足动物则不具有。澳大利亚肺鱼成熟蛋白的整体序列与四足动物（69%至84%）的相似性也高于与硬骨鱼（57%至74%）的相似性。这些关于肺鱼和其他脊椎动物之间α亚基前体分子关系的结果与最近的分子系统发育研究一致，表明肺鱼与四足动物的关系比与硬骨鱼的关系更密切。我们还发现，肺鱼α亚基的一级结构与恒温脊椎动物的一级结构相比，与两栖动物的一级结构略有但显著更相似。这可能是由于两栖动物α亚基分子的特化。
