Stallmeyer B, Drugeon G, Reiss J, Haenni A L, Mendel R R
Botanisches Institut der Technischen Universität, Braunschweig, Humboldtstr. 1, D-38106 Braunschweig, Germany.
Am J Hum Genet. 1999 Mar;64(3):698-705. doi: 10.1086/302295.
A universal molybdenum-containing cofactor (MoCo) is essential for the activity of all human molybdoenzymes, including sulphite oxidase. The free cofactor is highly unstable, and all organisms share a similar biosynthetic pathway. The involved enzymes exhibit homologies, even between bacteria and humans. We have exploited these homologies to isolate a cDNA for the heterodimeric molybdopterin (MPT)-synthase. This enzyme is necessary for the conversion of an unstable precursor into molybdopterin, the organic moiety of MoCo. The corresponding transcript shows a bicistronic structure, encoding the small and large subunits of the MPT-synthase in two different open reading frames (ORFs) that overlap by 77 nucleotides. In various human tissues, only one size of mRNA coinciding with the bicistronic transcript was detected. In vitro translation and mutagenesis experiments demonstrated that each ORF is translated independently, leading to the synthesis of a 10-kDa protein and a 21-kDa protein for the small and large subunits, respectively, and indicated that the 3'-proximal ORF of the bicistronic transcript is translated by leaky scanning.
一种通用的含钼辅因子（MoCo）对于包括亚硫酸盐氧化酶在内的所有人类钼酶的活性至关重要。游离的辅因子高度不稳定，并且所有生物体都共享相似的生物合成途径。所涉及的酶表现出同源性，甚至在细菌和人类之间也是如此。我们利用这些同源性分离出了异二聚体钼蝶呤（MPT）合酶的cDNA。这种酶对于将不稳定的前体转化为钼蝶呤（MoCo的有机部分）是必需的。相应的转录本呈现双顺反子结构，在两个不同的开放阅读框（ORF）中编码MPT合酶的小亚基和大亚基，这两个开放阅读框重叠77个核苷酸。在各种人类组织中，仅检测到一种与双顺反子转录本一致大小的mRNA。体外翻译和诱变实验表明，每个ORF都是独立翻译的，分别导致小亚基和大亚基合成10 kDa的蛋白质和21 kDa的蛋白质，并表明双顺反子转录本的3'近端ORF通过渗漏扫描进行翻译。
