Translation efficiencies of synonymous codons are not always correlated with codon usage in tobacco chloroplasts
Translation efficiencies of synonymous codons are not always correlated with codon usage in tobacco chloroplasts
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DOI：
10.1111/j.1365-313x.2006.02945.x
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发表时间：
2007-01-01
期刊：
影响因子：
7.2
通讯作者：
Sugiura, Masahiro
中科院分区：
文献类型：
--
作者：
Nakamura, Masayuki;Sugiura, Masahiro
叶绿体中的密码子使用不同于原核和真核细胞的核基因组。然而，还没有实验方法来分析叶绿体中单个密码子的翻译效率。我们设计了一个体外翻译效率测定使用合成的mRNA，并测量了烟草叶绿体中的5个同义密码子组的翻译效率。在四种丙氨酸密码子（GCN，其中N是U，C，A或G）中，GCU是最有效的翻译，而叶绿体基因组缺乏对应于GCU的tRNA基因。苯丙氨酸和酪氨酸分别由两个密码子（分别为UUU/C和UAU/C）编码。苯丙氨酸UUC和酪氨酸UAC的翻译效率分别是UUU和UAU的两倍以上，与它们的密码子使用相反，而丙氨酸，天冬氨酸和天冬酰胺的同义密码子的翻译效率与它们的密码子使用平行。这些观察结果表明，单个密码子的翻译效率并不总是与密码子的使用在体外叶绿体。这就为外源基因在叶绿体中的表达提出了一个重要的问题。
Codon usage in chloroplasts is different from that in prokaryotic and eukaryotic nuclear genomes. However, no experimental approach has been made to analyse the translation efficiency of individual codons in chloroplasts. We devised an in vitro assay for translation efficiencies using synthetic mRNAs, and measured the translation efficiencies of five synonymous codon groups in tobacco chloroplasts. Among four alanine codons (GCN, where N is U, C, A or G), GCU was the most efficient for translation, whereas the chloroplast genome lacks tRNA genes corresponding to GCU. Phenylalanine and tyrosine are each encoded by two codons (UUU/C and UAU/C, respectively). Phenylalanine UUC and tyrosine UAC were translated more than twice as efficiently than UUU and UAU, respectively, contrary to their codon usage, whereas translation efficiencies of synonymous codons for alanine, aspartic acid and asparagine were parallel to their codon usage. These observations indicate that translation efficiencies of individual codons are not always correlated with codon usage in vitro in chloroplasts. This raises an important issue for foreign gene expression in chloroplasts.