Choi I S, Diamond A M, Crain P F, Kolker J D, McCloskey J A, Hatfield D L
Laboratory of Experimental Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892.
Biochemistry. 1994 Jan 18;33(2):601-5. doi: 10.1021/bi00168a027.
Selenocysteine is cotranslationally introduced into a growing polypeptide in response to certain UGA codons in selenoprotein mRNAs. The biosynthesis of this amino acid initiates by aminoacylation of specific tRNAs (designated tRNA([Ser]Sec)) with serine and subsequent conversion of the serine moiety to selenocysteine. The resulting selenocysteyl-tRNA then donates selenocysteine to protein. In most higher vertebrate cells and tissues examined, multiple selenocysteine isoacceptors have been described. Two of these have been determined to differ by only a single modified residue in the wobble position of the anticodon. In addition, the steady-state levels and relative distributions of these isoacceptors have been shown to be influenced by the presence of selenium. In order to gain a better understanding of the relationship between these tRNAs and how they are regulated, both the Xenopus selenocysteine tRNA gene and an in vitro synthesized RNA have each been injected into Xenopus oocytes and their maturation analyzed. In this system, selenium enhanced RNA stability and altered the distribution of isoacceptors that differ by a single ribose methylation. Interestingly, the biosynthesis of one of these modified nucleosides (5-methylcarboxymethyl-2'-O-methyluridine), which has been identified only in the wobble position of selenocysteine tRNA, also occurs in oocytes. Examination of the modified residues in both the naturally occurring Xenopus selenocysteine tRNA and the products generated from exogenous templates in oocytes demonstrated the faithful reconstruction of the biosynthetic pathway for these tRNAs.
硒代半胱氨酸在硒蛋白mRNA中的某些UGA密码子的作用下，共翻译引入到正在生长的多肽中。这种氨基酸的生物合成通过特定tRNA（称为tRNA([Ser]Sec)）与丝氨酸的氨酰化开始，随后丝氨酸部分转化为硒代半胱氨酸。生成的硒代半胱氨酰-tRNA然后将硒代半胱氨酸提供给蛋白质。在大多数已检测的高等脊椎动物细胞和组织中，已描述了多种硒代半胱氨酸同工受体。其中两种已确定仅在反密码子摆动位置的一个修饰残基上有所不同。此外，这些同工受体的稳态水平和相对分布已显示受硒的存在影响。为了更好地理解这些tRNA之间的关系以及它们如何被调控，非洲爪蟾硒代半胱氨酸tRNA基因和体外合成的RNA分别被注射到非洲爪蟾卵母细胞中，并分析它们的成熟情况。在这个系统中，硒增强了RNA稳定性，并改变了仅在一个核糖甲基化上不同的同工受体的分布。有趣的是，这些修饰核苷之一（5-甲基羧甲基-2'-O-甲基尿苷）的生物合成，仅在硒代半胱氨酸tRNA的摆动位置被鉴定出，也发生在卵母细胞中。对天然存在的非洲爪蟾硒代半胱氨酸tRNA和卵母细胞中外源模板产生的产物中的修饰残基进行检查，证明了这些tRNA生物合成途径的忠实重建。
