Nagoya City University, Mizuhocho Yamanohata, Mizuho, Japan.
Gene. 2011 Feb 1;472(1-2):50-4. doi: 10.1016/j.gene.2010.09.008. Epub 2010 Oct 13.
Codon usage in chloroplast mRNAs is different from that in prokaryotic and cytosolic mRNAs. We previously devised an in vitro assay for translation efficiencies using synthetic mRNAs, and measured translation efficiencies of five synonymous codon groups in tobacco chloroplasts. Using this assay, we here report our analysis of four additional synonymous codon groups in tobacco chloroplasts. We found that translation efficiencies of three arginine codons AGA, CGU and CGA differ dramatically, ca. 10-fold difference although the three arginine codons possess similar codon usage. Translation of AGA is very high, while CGA is translated extremely low. CGA is used frequently in chloroplasts but rare in Escherichia coli. The single tRNA species reads two histidine codons (CAU and CAC) and this is also the case for two glutamic acid codons (GAA and GAG) and two arginine codons (GCU and GCA). Their translation efficiencies, however, differ significantly. These observations suggest that individual codons posses their intrinsic efficiencies.
叶绿体 mRNA 的密码子使用与原核生物和细胞质 mRNA 不同。我们之前设计了一种使用合成 mRNA 的体外翻译效率测定法，并测量了烟草叶绿体中五个同义密码子组的翻译效率。使用该测定法，我们在此报告了对烟草叶绿体中另外四个同义密码子组的分析。我们发现，尽管三个精氨酸密码子具有相似的密码子使用，但 AGA、CGU 和 CGA 三个精氨酸密码子的翻译效率差异很大，相差约 10 倍。AGA 的翻译效率很高，而 CGA 的翻译效率极低。CGA 在叶绿体中使用频繁，但在大肠杆菌中很少使用。单个 tRNA 可以读取两个组氨酸密码子（CAU 和 CAC），而两个谷氨酸密码子（GAA 和 GAG）和两个精氨酸密码子（GCU 和 GCA）也是如此。然而，它们的翻译效率差异很大。这些观察结果表明，单个密码子具有内在的效率。
