The S open reading frame of the hepatitis B virus (HBV) comprises preS1 region, preS2 region, and S structural gene region, which code the large middle and major surface antigen polypeptides, respectively, in accordance with translation from the three in-frame initiation codons. In order to investigate the most important sequence within the preS2 promoter region, plasmids were created with serial deletion mutants directing the expression of the chloramphenicol acetyl transferase gene and the transcriptional activities were analyzed by transfection assays in four human hepatocellular carcinoma or hepatoblastoma cell lines (HepG2, PLC/PRF/5, Hep3B, and 2.2.15). Deletion mutant analysis revealed that the promoter from sequence 2861 to 2887 had highest activity. Two binding sites for nuclear proteins were observed by DNase I footprinting assay but multiple shifted DNA bands were identified by gel retardation assay suggesting that there are multiple binding sites for nuclear protein in the promoter sequence between nucleotides 2920 and 2951.
