SELENOCYSTEINE, THE 21ST AMINO ACID IN THE GENETIC CODECURRING AMINO ACID

已分离到两个硒半胱氨酸tRNA，并对其进行了鉴定 这个实验室里的哺乳动物细胞。他们读取了终止密码子UGA， 在蛋白质合成中，从而为生长中的 对UGA密码子作出反应的多肽链。……的生物合成 硒半胱氨酸存在于tRNA等位受体上，其途径是 TRNA[Ser]Sec-&gt；Seryl-tRNA[Ser]Sec-&gt；Phoseryl-tRNA[Ser]Sec-&gt； 硒半胱基-tRNA[Ser]Sec.这两种同种受体都来自单一拷贝基因 在分离出基因的每一种生物中， 已排序。这些生物包括人、兔子、鸡、非洲爪哇、 果蝇和线虫。该基因的转录受 几个上游地区。出现该基因的内部控制区 口述转录开始的位置，以及播放 在初级成绩单的3‘端处理过程中的作用。两个人 异位受体基因产物相差5个嘧啶 在分子的5‘半部分发生的跃迁。因此，一个 等受体很可能是另一个的编辑版本。添加硒 在哺乳动物细胞的培养液中诱导编辑 硒半胱氨酸异构体。我们还展示了UGA密码子在 谷胱甘肽过氧化物酶编码终止和硒半胱氨酸， 证明了这种密码子在遗传密码中的双重作用。此外, 在酵母和藻类中发现了一种硒半胱氨酸tRNA 该UGA同时用于终止和硒半胱氨酸在 通用遗传密码。

Two selenocysteine tRNAs have been isolated and characterized from mammalian cells in this laboratory. They read the termination codon, UGA, in protein synthesis and thus donate selenocysteine to the growing polypeptide chain in response to UGA codons. The biosynthesis of selenocysteine occurs on the tRNA isoacceptors and its pathway is tRNA[Ser)Sec ---> seryl-tRNA[Ser]Sec --- > phosphoseryl-tRNA[Ser]Sec --- > selenocysteyl-tRNA[Ser]Sec. Both isoacceptors arise from a single copy gene in each of the organisms from which the gene has been isolated and sequenced. The organisms include human, rabbit, chicken, Xenopus, Drosophila and C. elegans. Transcription of the gene is regulated by several upstream regions. The internal control regions of the gene appear to dictate the site of initiation of transcription, as well as playing a role in processing at the 3' end of the primary transcript. The two isoacceptor gene products differ from each other by five pyrimidine transitions which occur in the 5' half of the molecule. Therefore, one isoacceptor is likely an edited version of the other. Addition of selenium to the media of mammalian cells in culture induces editing of the selenocysteine isoacceptors. We have also shown that the UGA codon in glutathione peroxidase codes for both termination and for selenocysteine, demonstrating the dual role of this codon in the genetic code. In addition, a selenocysteine TRNA has been found in yeast and in algae demonstrating that UGA is used for both termination and selenocysteine within the universal genetic code.