Izant J G, Bryson L J
Department of Genetics, Yale School of Medicine, New Haven, Connecticut 06510.
J Biol Chem. 1991 Oct 5;266(28):18560-6.
We have isolated cDNAs encoding annexin II (calpactin I) heavy chain homologues from a Xenopus oocyte cDNA library. Two of the clones are full length, while two appear to be derived from incompletely spliced mRNAs. The 1230- and 1240-base pair full length clones are 99% identical, and both have 84 bases of 5'-untranslated sequence, 1020-base open reading frames, and either 126- or 136-base 3'-untranslated domains. Northern blots show a 1.4-kilobase (kb) annexin II heavy chain transcript throughout oogenesis and in mature eggs. Xenopus annexin II mRNA levels are constant during early embryogenesis, but decrease at 8 h. After midblastula transition, the steady state level of the 1.4-kb transcript increases substantially, and a 3.3-kb transcript appears. Adult brain, heart, striated muscle, and liver contain moderate amounts of the 1.4-kb transcript, while skin has the 3.3-kb transcript and very high levels of the 1.4-kb transcript. Synthetic mRNA derived from the Xenopus annexin II cDNAs directs the synthesis of an apparent Mr = 36,500 polypeptide when microinjected into Xenopus oocytes. The predicted 339-amino acid protein products are 80% identical with murine annexin II heavy chain. Most of the differences are concentrated in the amino end from residues 15 to 24. The Xenopus annexin II heavy chain lacks the highly conserved tyrosine at position 23 which is the site of src oncogene tyrosine kinase phosphorylation in the murine protein. These results demonstrate that Xenopus oocytes contain an annexin II (calpactin I) heavy chain mRNA with a distinct amino terminus and suggest that multiple annexin II isoforms may be expressed during amphibian embryogenesis and development.
我们从非洲爪蟾卵母细胞cDNA文库中分离出了编码膜联蛋白II（钙结合蛋白I）重链同源物的cDNA。其中两个克隆是全长的，而另外两个似乎来源于未完全剪接的mRNA。这两个1230和1240碱基对的全长克隆有99%的同源性，都有84个碱基的5'非翻译序列、1020碱基的开放阅读框，以及126或136碱基的3'非翻译区。Northern印迹显示，在整个卵子发生过程以及成熟卵中都有一条1.4千碱基（kb）的膜联蛋白II重链转录本。非洲爪蟾膜联蛋白II mRNA水平在早期胚胎发育过程中保持恒定，但在8小时时下降。在中囊胚转换之后，1.4-kb转录本的稳态水平大幅增加，并且出现了一条3.3-kb的转录本。成年脑、心脏、横纹肌和肝脏含有适量的1.4-kb转录本，而皮肤既有3.3-kb转录本，也有非常高水平的1.4-kb转录本。当将源自非洲爪蟾膜联蛋白II cDNA的合成mRNA显微注射到非洲爪蟾卵母细胞中时，它指导合成了一种表观分子量为36,500的多肽。预测的339个氨基酸的蛋白质产物与小鼠膜联蛋白II重链有80%的同源性。大多数差异集中在第15至24位残基的氨基末端。非洲爪蟾膜联蛋白II重链在第23位缺乏高度保守的酪氨酸，而该酪氨酸是小鼠蛋白中src癌基因酪氨酸激酶磷酸化的位点。这些结果表明，非洲爪蟾卵母细胞含有一种具有独特氨基末端的膜联蛋白II（钙结合蛋白I）重链mRNA，并提示在两栖动物胚胎发生和发育过程中可能表达多种膜联蛋白II同工型。
