Yamao F, Muto A, Kawauchi Y, Iwami M, Iwagami S, Azumi Y, Osawa S
Proc Natl Acad Sci U S A. 1985 Apr;82(8):2306-9. doi: 10.1073/pnas.82.8.2306.
UGA is a nonsense or termination (opal) codon throughout prokaryotes and eukaryotes. However, mitochondria use not only UGG but also UGA as a tryptophan codon. Here, we show that UGA also codes for tryptophan in Mycoplasma capricolum, a wall-less bacterium having a genome only 20-25% the size of the Escherichia coli genome. This conclusion is based on the following evidence. First, the nucleotide sequence of the S3 and L16 ribosomal protein genes from M. capricolum includes UGA codons in the reading frames; they appear at positions corresponding to tryptophan in E. coli S3 and L16. Second, a tRNATrp gene and its product tRNA found in M. capricolum have the anticodon sequence 5' U-C-A 3', which can form a complementary base-pairing interaction with UGA.
在整个原核生物和真核生物中，UGA是一个无义或终止（乳白）密码子。然而，线粒体不仅使用UGG，还使用UGA作为色氨酸密码子。在这里，我们表明UGA在山羊支原体中也编码色氨酸，山羊支原体是一种无细胞壁的细菌，其基因组大小仅为大肠杆菌基因组的20%-25%。这一结论基于以下证据。首先，来自山羊支原体的S3和L16核糖体蛋白基因的核苷酸序列在阅读框中包含UGA密码子；它们出现在大肠杆菌S3和L16中对应色氨酸的位置。其次，在山羊支原体中发现的一个tRNATrp基因及其产物tRNA具有反密码子序列5'U-C-A 3'，它可以与UGA形成互补碱基配对相互作用。
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