Regulation of chicken ornithine transcarbamylase gene.

鸟氨酸转氨甲酰酶[OTC，EC 2.1.3.3]是尿素循环酶之一。鸡体内的这种酶没有生理上的必要性，因为鸡是一种排尿酸的动物。然而，在鸡中，少数在其肾脏中显示相对较高的OTC活性。项目负责人建立了两个鸡系;一个显示出较高的OTC活性，另一个在肾脏中没有活性。在鸡中观察到OTC活性的异常组织特异性表达，即，在鸡的几乎所有器官中，OTC的mRNA都被转录和翻译，但翻译的蛋白质不被这些器官中的线粒体加工，只有肾脏显示OTC活性。为了从分子水平上阐明这些现象，有必要克隆鸡肾OTC基因。本研究克隆了鸡肾OTC基因的cDNA，并测定了其核苷酸序列.并与大鼠肝和人肝的序列进行了比较。在成熟蛋白部分，鸡OTC与大鼠和人OTC的序列高度保守，但在前导肽部分，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OTC mRNA均表达。然而，使用多个引物组的实验表明，这两个器官的OTC mRNA的5 '-DNA序列与肾脏的不同。

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.