Fearnley I M, Walker J E
MRC Laboratory of Molecular Biology, Cambridge, U.K.
Biochemistry. 1987 Dec 15;26(25):8247-51. doi: 10.1021/bi00399a034.
The bovine mitochondrial gene products ND2 and ND4, components of NADH dehydrogenase, have been purified from a chloroform/methanol extract of mitochondrial membranes, and the human mitochondrial gene products ND2 and cytochrome b have been obtained by similar procedures. They have been identified by comparison of their amino-terminal protein sequences with those predicted from DNA sequences of bovine and human mitochondrial DNA. All of the proteins have methionine as their amino-terminal residue. In bovine ND2, this residue is encoded by the "universal" isoleucine codon AUA, and the sequences of human cytochrome b and bovine ND2 demonstrate that AUA also encodes methionine in the elongation step of mitochondrial protein synthesis. In human ND2, the amino-terminal methionine is encoded by AUU, which, as in the "universal" genetic code, is also used as an isoleucine codon in elongation. Thus, AUU has a dual coding function which is dependent upon its context.
牛线粒体基因产物ND2和ND4是NADH脱氢酶的组成部分，已从线粒体膜的氯仿/甲醇提取物中纯化出来，而人线粒体基因产物ND2和细胞色素b也通过类似方法获得。通过将它们的氨基末端蛋白质序列与从牛和人线粒体DNA序列预测的序列进行比较，对它们进行了鉴定。所有这些蛋白质的氨基末端残基都是甲硫氨酸。在牛ND2中，该残基由“通用”异亮氨酸密码子AUA编码，人细胞色素b和牛ND2的序列表明，在线粒体蛋白质合成的延伸步骤中，AUA也编码甲硫氨酸。在人ND2中，氨基末端甲硫氨酸由AUU编码，与“通用”遗传密码一样，AUU在延伸过程中也用作异亮氨酸密码子。因此，AUU具有双重编码功能，这取决于其上下文。
