Structure and expression of the hepatitis B virus genome.

By fusion of the hepatitis B virus (HBV) surface antigen (HBsAg) gene to that of the E. coli lac Z gene carried by a phage lambda derivative, expression of HBsAg antigenic determinants was obtained and carried by a 138,000 dalton fusion polypeptide. Such a protein could be ultimately useful for second generation vaccine production. HBsAg gene expression was studied in eukaryotic cells using the mouse L cell (tk-) system. Cotransformation using a plasmid carrying two copies of the HBV genome in a tandem, head-to-tail arrangement (pCP10) and the cloned HSV-1 tk gene resulted in the excretion of 22 nm HBsAg particles in the supernatant. No other HBV markers were detected. These particles possess the same characteristics as the human serum particles (morphology, diameter, density, antigenicity). The purified HBsAg particles from L cells were found to be highly immunogenic in mice. HBV mRNA transcripts from these cells were analysed by Northern blotting. A major species of 2,300 bases was detected. This was mapped on the genome by hybridization with subgenomic fragments and in the L cell system using a series of plasmid derivatives carrying insertions at specific sites in the HBV genome and assaying for HBsAg expression. Thus the HBsAg gene promotor was localized between positions 2,400-2,800. Indeed there is only one TATA like sequence in this region, starting at position 2,776.