Objective:To construct tetracycline regulating expression system of HBV-S gene

and study its regulating expression of HBVAg by tetracycline in HepG 2 cells. Methods:Insert HBs gene into the multiple cloning site of pcDNA4

which contain tetracycline operator in the promoter

and the constructed vector with pcDNA6 was co-transferred into HepG2 by means of lipofectamine

and use 400μg/ml Zeocin and 10μg/ml Blasticidin to kill the untransfected host cell line. After 20 days’select

the cell line which express HBsAg stablely after induced by tetracycline was generated. Then the HBsAg expressing was induced by varying concentration of tetracycline(0.5μg/ml

1.0μg/ml

2.0μg/ml

3.0μg/ml).Amount of HBsAg was detected by means of MEIA (Microparticle Enzyme Immunoassay) to determine the appropriate concentration of tetracycline. Result:HBsAg had been expressed at low quantity without tetracycline in transfected HepG2. However the S/N of HBsAg were high but not different after induced by varying concentration of tetracycline. Conclusion:Tetracycline regulating expression system of HBV-S gene was constructed successfully and HBsAg was highly expressed in the vector induced by tetracycline.