Expression and replication of the hepatitis B virus genome under foreign promoter control.

A novel expression system was established that allows expression and propagation of the human hepatitis B virus (HBV) genome in cultured animal cells. An overlength HBV genome encoding the viral pregenomic RNA was put under transcriptional control of the human metallothionein IIA promoter thereby replacing the endogenous HBV core gene promoter. Transient expression of this construct in hepatoma cells resulted in formation of particles indistinguishable from HBV (Dane particles). Uncoupling of the promoter from overlapping HBV genes facilitated a mutational analysis of HBV gene functions. For example, removal of the preC start codon completely prevented HBeAg synthesis whereas formation of HBV-like particles remained unaffected. In addition, overexpression of the core gene led to detection of minor and otherwise undetectable core gene products, including a core/pol fusion protein and larger precursor molecules of the secreted HBeAg.