THE ROLE OF SELENIUM IN CELLULAR METABOLISM

饮食中硒的过量和缺乏都不利于 健康和证据表明，这种元素在癌症，心脏病， 疾病和衰老过程中。 由于硒发挥其作用， 至少在某种程度上，通过它在蛋白质中的存在，我们的目标是了解 这种迷人的元素是如何被整合到蛋白质中的 因此，我们 研究了参与以硒的形式捐赠硒的tRNA， 硒代半胱氨酸转化为蛋白质。 在过去的一年里，我们已经表明， 大鼠肝脏硒代半胱氨酸转运蛋白的一级序列与 相应的硒代半胱氨酸tRNA基因序列， 这些异源受体的结构不同之处在于单个2 ′-O-核糖 反密码子摆动位置的甲基化。 甲基化 核苷是一个新发现的部分，在任何其他tRNA中都没有观察到。 在这些tRNA中有三个额外的修饰核苷。 爪蟾 硒代半胱氨酸tRNA也仅含有四个修饰的核苷， 有趣的是，这四个修饰部分与在大鼠中发现的相同， 肝种属。 爪蟾硒代半胱氨酸转运蛋白的生物合成 卵母细胞来自基因或来自合成RNA（从 克隆到表达载体中的基因）显示，四个修饰的 形成了核苷，并且硒代半胱氨酸tRNA 向甲基化衍生物的群体发生响应于 硒。 设计了一种核糖体结合试验，证明 硒代半胱氨酸-tRNA不与正常的延伸因子相互作用， EFalpha-1，提供了这种独特的tRNA具有自身延伸的证据 因子 有趣的是，硒代半胱氨酸tRNA的丝氨酰-tRNA形式 与EFalpha-1相互作用，尽管很弱，这证实了我们先前的研究结果。 发现这种tRNA可以抑制蛋白质合成中的UGA密码子。 丝氨酸-tRNA合成酶的硒代半胱氨酸和丝氨酸tRNA的鉴定 正在被确定。 总共进行了22次单独的突变 在受体茎内和额外环中（同源性的共同位点） 对应的tRNA基因。 这些产品的能力 被丝氨酰-tRNA合成酶氨酰化的突变体形式目前 正在接受检查。

Excesses and deficiencies of selenium in the diet are detrimental to health and evidence suggests that this element has a role in cancer, heart disease and in the aging process. Since selenium exerts its effects, at least in part, through its presence in protein, our goal is to understand how this fascinating element is incorporated into protein. Thus, we are studying the tRNAs involved in donating selenium in the form of selenocysteine into protein. In the past year, we have shown that the primary sequence of the rat liver selenocysteine tRNAs are colinear with the corresponding selenocysteine tRNA gene sequence and that the structures of these isoacceptors differ by a single 2'-0-ribose methylation in the wobble position of the anticodon. The methylated nucleoside is a newly discovered moiety, not observed in any other tRNA. There are three additional modified nucleosides in these tRNAs. Xenopus selenocysteine tRNA also contains only four modified nucleosides and, interestingly, these are the same four modified moieties found in the rat liver species. Biosynthesis of the selenocysteine tRNAs in Xenopus oocytes from either the gene or from synthetic RNA (generated from the gene cloned into an expression vector) shows that the four modified nucleosides are formed and that a shift in the selenocysteine tRNA population toward the methylated derivative occurs in response to selenium. A ribosomal binding assay was devised which demonstrated that selenocysteyl-tRNA does not interact with the normal elongation factor, EFalpha-1, providing evidence that this unique tRNA has its own elongation factor. Interestingly, the seryl-tRNA form of selenocysteine tRNA did interact, albeit weakly, with EFalpha-1 which substantiated our earlier findings that this tRNA can suppress UGA codons in protein synthesis. Identity of the selenocysteine and serine tRNAs for seryl-tRNA synthetase is being determined. A total of 22 individual mutations has been made within the acceptor stem and in the extra loop (common sites of homology) in the corresponding tRNA genes. The ability of the products of these mutant forms to be aminoacylated by seryl-tRNA synthetase is presently being examined.