THE ROLE OF SELENIUM IN CELLULAR METABOLISM

硒元素是哺乳动物饮食所必需的， 饮食中这种元素的缺乏范围很窄， 对健康有害。 大量证据支持 硒在预防癌症和心脏病方面的作用， 衰老过程的开始 当硒发挥其细胞效应时， 至少部分地，作为蛋白质中的氨基酸硒代半胱氨酸， 试图阐明硒代半胱氨酸被掺入的机制， 转化成蛋白质 硒代半胱氨酸在细胞中的生物合成发生在其 tRNA首先被丝氨酸氨酰化。 在过去的一年里，我们 在人类细胞系中发现了几种新的硒代半胱氨酸转运蛋白， 结果提出了这些异源受体中的一些可能性， 由于编辑。 此外，我们已经表明，TATA盒和 近端序列元件足以用于基础水平转录 的基因。 这些结果不同于所有其他已知的真核基因 它们的基因中含有控制元件。 转录 发现起始位点由TATA之间的距离决定 框和起始位置。 非洲爪蟾硒代半胱氨酸tRNA基因被发现 更像Pol II而不是Pol III基因的转录， 基因由Pol III转录。 丝氨酸-tRNA-[Ser] Sec和硒代半胱氨酸- 检查了tRNA-[Ser] Sec的能力，以提供相应的 氨基酸到蛋白质。 丝氨酸是对密码子UGA的应答， 抑制这个密码子，而硒代半胱氨酸只在体内捐赠， 对硒代胱氨酸UGA密码子的应答。 这些结果提供了强有力的 插入中涉及特定延伸因子的证据 硒代半胱氨酸转化为蛋白质的反应 密码子 硒代半胱氨酸和丝氨酸tRNA被氨酰化， 由相同的丝氨酰-tRNA合成酶合成，这些tRNA具有非常相似的 身份的地点。 硒代半胱氨酸可以插入到蛋白质中， 对UAA和UUA密码子的应答，条件是硒代半胱氨酸tRNA含有 与相应密码子互补的反密码子， 这表明，UGA是不需要的。

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.