[Translation initiation function of the regulation element in the operon of cholera toxin A]

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