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

两个硒代半胱氨酸转运蛋白已被分离和表征， 在这个实验室里的哺乳动物细胞。他们读取了终止密码子UGA， 在蛋白质合成中起重要作用， 多肽链中响应UGA密码子。的生物合成 硒代半胱氨酸发生在tRNA异源受体上，其途径是 tRNA[Ser] Sec -> seryl-tRNA[Ser]Sec - > phosphoseryl-tRNA[Ser]Sec - > 硒代半胱氨酸-tRNA [Ser]Sec.这两种同种受体都来自一个单拷贝基因 在每一个已经分离出该基因的生物体中， 测序这些生物包括人类、兔子、鸡、非洲爪蟾， 果蝇和C.优雅该基因的转录受 上游地区。基因的内部控制区域 来决定转录起始的位置，以及播放一个 在初级转录物的3'端加工中的作用。两 同种受体基因产物彼此不同， 发生在分子5'端的跃迁。因此，一 isoacceptor可能是另一个的编辑版本。添加硒 哺乳动物细胞的培养基中诱导编辑 硒代半胱氨酸异受体。我们还表明，UGA密码子在 谷胱甘肽过氧化物酶编码终止和硒代半胱氨酸， 证明了这个密码子在遗传密码中的双重作用。此外，本发明还提供了一种方法， 在酵母和藻类中发现了硒代半胱氨酸tRNA， UGA用于终止和硒代半胱氨酸， 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.