翻译偶联对霍乱毒素A、B亚基比例表达的影响

Translation coupling: effect on the gene expression in the operon of cholera toxin

目的：证实霍乱毒素操纵子Ａ、Ｂ基因间存在翻译偶联，解释霍乱毒素Ｂ亚基基因表达水平是Ａ 亚基５ 倍的机理。方法：构建了适合翻译调控研究的报告质粒，通过在ｃｔｘＡ 基因５′及３′端进行移码突变，研究突变对Ｂ亚基基因表达水平的影响。结果：建立了合适的研究霍乱毒素基因翻译调控的系统，在ｃｔｘＡ 基因的近Ｃ端移码突变后，Ｂ基因的表达水平降低到１／５（８０％ ）。结论：霍乱毒素Ａ、Ｂ亚基基因间存在翻译偶联调控，这种调控是霍乱毒素Ａ、Ｂ亚基比例表达的机理之一。

Objective: To demonstrate the existence of translation coupling between cholera toxin A subunit gene and B subunit gene, and to elucidate why the expression level of B gene is five times more than that of A gene. Methods: A report system for the investigation of translation coupling was constructed by using lacZ gene as the reporter, and frame shift mutation was introduced near the C terminal of ctxA gene so the ribosome would read through its normal stop codon. Results: The report plasmid was constructed and it was found that the expression level of lacZ gene decreased by five times after the frame shift mutation. Conclusion: The translation of cholera toxin B subunit gene was coupled with A subunit gene by translational coupling, and was responsible for the differential expression level of the two genes.