霍乱毒素B亚基基因具有自己的启动子

A Promoter Responsible for Over-expression of Cholera Toxin B Subunit in Cholera Toxin A Subunit Structure Gene

本研究发现并证实霍乱毒素B亚基基因上游Xba Ⅰ～Cla Ⅰ限制性片段内存在具有启动子活性的序列;在该启动子作用下,霍乱毒素B亚基表达水平可达200mg/L,氯霉素乙酰基转移酶基因表达水平随培养条件不同在0.3～10mg/L之间,大肠杆菌β-半乳糖苷酶基因的表达量达4100U/ml。在该启动子的控制下霍乱毒素B亚基基因可以高效表达,该启动子的存在可能是由于霍乱毒素操纵子中霍乱毒素B亚基表达量是A亚基的6倍。

A promoter sequence, which promotes the transcription of cholera toxin B subunit gene, was found in cholera toxin A subunit structure gene. The transcription starts at the aclenine 456 bp upstream to the A of the initiation codon ATG of cholera toxin B gene. Under the control of the promoter, cholera toxin B subunit was over-expressed as high as 200 mg/L at an optimized culture condition; the chloramphemcol acetyl transferase gene and (-galactosidase could also be efficiently expressed under the direction of the promoter. The existence of the promoter may be responsible for the 6 fold and 7 fold higher expression level of cholera toxin B subunit than cholera toxin A subunit in V. cholerae and Eschena coll respectively. The over-expression of CTB may assist in preparing vaccine against cholera and facilitating the construction of peptide-bearing immunogenic hybrid proteins.