Information of codon usage bias has been used for modifying genes for improved expression in heterologous systems. Codon modifications are carried out using the species-specific codon usage so that they reflect the codon usage pattern of the host, without modifying the amino acid sequence of the encoded protein. In the present study we analyzed the effect of codon optimization on the expression of the bacterial gene bar in tobacco. In order to identify the percentage of optimal codons needed to achieve high levels of protein expression, bar genes with different percentage and placement of optimal codons were analyzed in transgenic tobacco lines. It was observed that there was no gain in bar protein expression when the percentage of optimal codons was increased from 63.9% (as observed in the wild type bar gene) to 93.9%. However, reducing the percentage of optimal codons to 54.0 led to a drop in the levels of the bar protein. Further, in silico analysis was also carried out in ~ 4500 genes present on chromosome 2 of Arabidopsis thaliana to study the distribution of optimal codons. It was observed that majority (88%) of the genes have 30–50% of optimal codons and none of the gene was found to have more than 80% of optimal codons. The present study showed that there may not be a one-to-one correlation between the percentage of optimal codons and the expression levels of the transgene. A certain percentage of optimal codons is probably enough to achieve high levels of transgene expression. Any increase in the percentage of optimal codons beyond this level may not necessarily lead to any further improvement in expression.

中文翻译：

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评估密码子优化对转基因烟草植物bar基因表达的影响

密码子使用偏倚的信息已用于修饰基因，以改善异源系统中的表达。使用物种特有的密码子用法进行密码子修饰，以便它们反映宿主的密码子用法模式，而无需修饰编码蛋白质的氨基酸序列。在本研究中，我们分析了密码子优化对烟草中细菌基因bar表达的影响。为了识别，以实现高水平的蛋白质表达的所需的最佳密码子的百分比，棒在转基因烟草品系中分析了具有不同百分比和最佳密码子位置的基因。观察到，当最佳密码子的百分比从63.9％（在野生型bar基因中观察到）增加到93.9％时，bar蛋白的表达没有增加。但是，将最佳密码子的百分比降低到54.0会导致bar蛋白水平的下降。此外，还对拟南芥第2号染色体上存在的约4500个基因进行了计算机分析研究最佳密码子的分布。据观察，大多数基因（88％）具有30–50％的最佳密码子，没有一个基因被发现具有超过80％的最佳密码子。本研究表明，最佳密码子的百分比与转基因的表达水平之间可能没有一对一的相关性。一定百分比的最佳密码子可能足以实现高水平的转基因表达。超过该水平的最佳密码子百分比的任何增加可能不一定导致表达的任何进一步改善。