Lee Y H, Chen B F, Wu S Y, Leu W M, Lin J J, Chen C W, Lo S C
Institute of Biochemistry, National Yang-Ming Medical College, Taipei, Taiwan.
Gene. 1988 May 15;65(1):71-81. doi: 10.1016/0378-1119(88)90418-0.
The melanin locus (melC) from Streptomyces antibioticus was previously shown to be composed of two open reading frames (ORFs), melC1 and melC2. The melC2 ORF codes for the polypeptide chain of tyrosinase (apotyrosinase). The function of melC1 is not known except that insertional mutation within it abolishes the tyrosinase activity. Here, we show that in Streptomyces lividans TK64 harboring melC1 mutated and melC2 intact (melC1- melC2+) plasmids, while there was no tyrosinase activity, melC transcript was synthesized and apotyrosinase could be detected. The apotyrosinase could be activated to a limited degree by incubation with copper ions, or by mixing the mycelial extract from a culture harboring a melC1- melC2+ (pPF950) plasmid with that from a culture containing a melC1+ melC2- (pSA1) plasmid. Complementation analysis showed that melC1 acted in trans on the tyrosinase gene expression. Together, these results suggest that melC1 encodes or regulates a copper-transfer protein serving an in vivo copper-donor function in the biosynthesis of active tyrosinase.
先前已表明，来自抗生链霉菌的黑色素基因座（melC）由两个开放阅读框（ORF），即melC1和melC2组成。melC2 ORF编码酪氨酸酶（脱辅基酪氨酸酶）的多肽链。除了其内部的插入突变会消除酪氨酸酶活性外，melC1的功能尚不清楚。在此，我们表明，在携带melC1突变且melC2完整（melC1- melC2+）质粒的变铅青链霉菌TK64中，虽然没有酪氨酸酶活性，但合成了melC转录本并且可以检测到脱辅基酪氨酸酶。通过与铜离子孵育，或者通过将携带melC1- melC2+（pPF950）质粒的培养物的菌丝体提取物与含有melC1+ melC2-（pSA1）质粒的培养物的菌丝体提取物混合，可以有限程度地激活脱辅基酪氨酸酶。互补分析表明，melC1对酪氨酸酶基因表达起反式作用。总之，这些结果表明，melC1编码或调节一种铜转运蛋白，该蛋白在活性酪氨酸酶的生物合成中发挥体内铜供体功能。
