THE ROLE OF SELENIUM IN CELLULAR METABOLISM

元素硒是哺乳动物和过量饮食所必需的，也是 饮食中这种元素在很小范围内的不足是 对健康有害的。广泛的证据支持这一事件 硒在预防癌症和心脏病方面的作用及其延缓作用 衰老过程的开始。当硒发挥其细胞效应时， 至少在一定程度上，作为蛋白质中的氨基酸硒半胱氨酸，我们是 试图阐明硒半胱氨酸被结合的机制 变成蛋白质。细胞中硒半胱氨酸的生物合成发生在其 首先与丝氨酸发生氨基酰化反应的tRNA。在过去的一年里，我们已经 在人类细胞系中发现了几个新的硒半胱氨酸tRNA，这些 结果增加了其中一些等位受体可能出现的可能性 作为编辑的结果。此外，我们已经证明了塔塔盒子和 近端序列元件对于基础水平转录是足够的 这种基因的。这些结果与所有其他已知的真核基因不同。 它们的基因中含有控制元件。抄写 发现起始点由塔塔之间的距离确定 框和起始点。发现了非洲爪哇的硒半胱氨酸tRNA基因 被转录得更像Pol II而不是Pol III的基因甚至认为 基因由Pol III转录。Seryl-tRNA-[Ser]Sec和Selencysteyl- TRNA-[Ser]SEC被检查其是否有能力捐赠相应的 氨基酸转化为蛋白质。丝氨酸被捐赠来回应密码子UGA， 为了抑制这个密码子，而硒半胱氨酸只在体内被捐赠 对硒半胱氨酸UGA密码子的反应。这些结果提供了强有力的 插入过程中涉及特定伸长系数的证据 特异性硒半胱氨酸UGA将硒半胱氨酸转化为蛋白质 密码子。发现硒半胱氨酸和丝氨酸tRNAs是氨基酰化的 由相同的丝氨酰-tRNA合成酶和这些tRNA共享非常相似 有身份的网站。硒半胱氨酸可以被插入到蛋白质中 对UAA和UUA密码子的反应，前提是硒半胱氨酸tRNA包含 一种与相应密码子互补的反密码子 重要的是，这表明UGA不是必需的。

The element selenium is required in the diet of mammals and excesses or deficiencies of this element in the diet within a narrow range are detrimental to health. A wide range of evidence supports the involvement of selenium in preventing cancer and heart disease and a role in delaying the onset of the aging process. As selenium exerts its cellular effects, at least in part, as the amino acid selenocysteine in protein, we are trying to elucidate the mechanism by which selenocysteine is incorporated into protein. The biosynthesis of selenocysteine in cells occurs on its tRNA which is first aminoacylated with serine. In the past year, we have found several new selenocysteine tRNAs in human cell lines and these results raise the possibility that some of these isoacceptors may arise as a result of editing. Further, we have shown that the TATA box and proximal sequence element are sufficient for basal level transcription of the gene. These results differ from all other known eukaryotic genes which contain control elements within their genes. The transcription start site was found to be determined by the distance between the TATA box and the start site. The Xenopus selenocysteine tRNA gene was found to be transcribed more like Pol II than Pol III genes even thought this gene is transcribed by Pol III. Seryl-tRNA-[Ser]Sec and selenocysteyl- tRNA-[Ser]Sec were examined for their ability to donate the corresponding amino acid to protein. Serine was donated in response to the codon, UGA, to suppress this codon, while selenocysteine was donated only in vivo in response to a selenocystine UGA codon. These results provide strong evidence that a specific elongation factor is involved in the insertion of selenocysteine into protein in response to specific selenocysteine UGA codons. Selenocysteine and serine tRNAs were found to be aminoacylated by the same seryl-tRNA synthetase and these tRNAs share very similar sites of identity. Selenocysteine can be inserted into protein in response to UAA and UUA codons, provided the selenocysteine tRNA contains an anticodon complementary to the corresponding codon which very importantly shows that UGA is not required.