Regulation of Hepatitis B Virus Gene Expression by Its Two Enhancers.

A linearized genome containing the entire HBV 3.5 kb mRNA transcriptional units was constructed. Based on it, a series of mutants with enhancer deletions or point mutations were generated. This system has served as a good model to study the regulation of hepatitis B virus gene expression by its two enhancers (ENI and ENII). The results showed that both ENI and ENII could increase the expression of HBsAg, and the two enhancers worked synergistically. They also could increase the expression of HBeAg, but the deletion of 2C and Ep of ENI had no effect on the expression of Hbe/cAg in the cytoplasm. The expression of C gene might be regulated mainly by ENII, but ENI could cooperate with the action of ENII. The data indicated that ENI and ENII might function differentially but cooperatively in regulation the transcription of the two 3.5 kb mRNAs which functioned distinctively.