The effect of upstream sequences to initiator on the expression of gene coding for hepatitis B core antigen

The nucleotide sequences of cloned adw hepatitis B core antigens (HBcAg) which have different levels of expression have been determined by dideoxy chain-terminating method. The results indicate that the different levels of gene expression is primarily due to the different structures of upstream sequences before the initiator of HBcAg genes. The hepatitis B core gene in the low-expressed clone forms a secondary structure before the initiator. This secondary structure has been removed by Bal-31 exonuclease in the high-expressed clone and half of the structure removed in the mid-expressed clone. It is apparent that the transcription/translation of the hepatitis B core gene is somehow blocked because of the secondary structure. Therefore, the amount of HBcAg synthesized in E. coli is dramatically reduced.