Preferences of synonymous codons and translational control during the chloroplast genome evolution

在叶绿体中，同义密码子的翻译效率并不总是与其密码子的使用相关。烟草叶绿体rps2基因含有许多具有高效翻译活性的密码子，而rps16基因则含有大量无效密码子。为了阐明密码子偏好是否影响这些mRNAs的翻译效率，我使用烟草叶绿体体外翻译系统分析了rps2和rps16mRNAs的翻译效率。我发现：(1)rps-16基因5‘端非编码区翻译活性较低，(2)rps-16基因的蛋白质编码区的翻译速度是rps-2基因的3倍，(3)密码子替换提高了rps-16基因的翻译效率。

In chloroplasts, the translation efficiencies of synonymous codons are not always correlated with their codon usage. Tobacco chloroplast rps2 mRNA contains many codons having efficient translation activity, whereas rps16 mRNA has a lot of inefficient codons. To elucidate whether the codon preference affect the translation efficiencies of these mRNAs, I analyzed the translation efficiencies of rps2 and rps16 mRNAs using the in vitro translation system from tobacco chloroplasts. I found that (1) 5'UTR of rps16 mRNA has less translation activity, (2) protein coding region of rps16 mRNA was translated about 3-times faster than that of rps2 mRNA, and (3) codon substitutions increased that translation efficiency of protein coding region of rps16 mRNA.