Expression and characterization of hepatitis B virus precore-core antigen in E. coli.

The hepatitis B virus core antigen, including the precore sequence (HBcAg-p25), was expressed at very high levels in bacteria. Three expression vectors were constructed in which the synthesis of HBcAg-p25 was controlled by the tac promoter, and the number of nucleotides between the bacterial ribosome binding site and the precore initiation codon was varied in order to maximize HBcAg-p25 synthesis. The relative amount of HBcAg-p25 polypeptide expressed by the different vectors was estimated by SDS-polyacrylamide gel electrophoresis and immunoblot. HBcAg-p25 was associated with an insoluble fraction of bacterial extracts and required ionic detergents for solubilization. Comparison by ELISA of the immunoreactivity of HBcAg with and without the precore sequence suggested that human anti-HBcAg IgG preferentially recognizes HBcAg lacking the precore sequence.