Regulation of chicken ornithine transcarbamylase gene.

鸟氨酸转氨基甲酰基酶[OTC， EC 2.1.3.3]是尿素循环酶之一。由于鸡是一种输尿管动物，因此在鸡体内对这种酶没有生理上的必要性。然而，在鸡的肾脏中，有一些显示出相对较高的OTC活性。项目负责人建立了两条养鸡线；一种显示出较高的OTC活性，而另一种在肾脏中没有活性。在鸡中，OTC活性的组织特异性表达异常，即在鸡的几乎所有器官中，OTC的mRNA都被转录和翻译，但翻译后的蛋白在这些器官中除了肾脏外不会被线粒体加工，因此只有肾脏显示OTC活性。为了在分子水平上阐明这些现象，有必要对鸡肾OTC基因进行分子克隆。我们克隆了鸡肾OTC的cDNA，并测定了其核苷酸序列。并与大鼠肝脏和人肝脏的序列进行了比较。在成熟蛋白部分，鸡OTC与大鼠和人OTC相比，序列高度保守，但在先导肽部分，差异明显。采用AP-PCR方法对鸡肝脏和胰腺中OTC mrna的性质进行了研究。在两个器官中均表达OTC mrna。然而，使用多个引物组的实验表明，两个器官OTC mRNA的5'-DNA序列与肾脏mRNA的不同。为了证实这些结果，需要从两个器官中获得几个OTC cDNA克隆。

Ornithine transcarbamylase [OTC, EC 2.1.3.3]is one of the urea cycle enzymes. There is no physiological necessity for the enzyme in chicken, because chicken is an uricoteric animal. In chicken, however, a few show relatively higher OTC activity in their kidney. The project head established two chicken lines ; one shows higher OTC activity and the other shows no activity in the kidney. Abnormal tissue-specific expression of OTC activity is observed in chicken, i.e., in almost all chicken organs, mRNA of OTC is transcripted and translated, but the translated protein would not be processed by mitochondria in these organs except in the kidney, so that only the kidney shows OTC activity. To elucidate these phenomenon at a molecular level, a molecular cloning of chicken kidney OTC gene is necessary. We have cloned cDNA of chicken kidney OTC and then the nucleotide sequence was determined. The sequence was compared with those of rat liver and of human liver. At the part of mature protein, the sequence of chicken OTC is highly conserved compared with those of rat and human OTC, but at the part of the leader peptide, the difference is obvious. Employing AP-PCR method, the nature of OTC mRNAs in the liver and the pancreas of chicken was investigated. In both organs OTC mRNAs were expressed. However, an experiment using several primer sets suggested that the 5'-DNA sequence of OTC mRNA of both organs differ from that of kidney mRNA.To confirm these results, it would be necessary to get several clones of OTC cDNA from both organs.