Expression of the precore region of an avian hepatitis B virus is not required for viral replication.

The core-antigen-coding region of all hepadnaviruses is preceded by a short, in-phase open reading frame termed precore whose expression can give rise to core-antigen-related polypeptides. To explore the functional significance of precore expression in vivo, we introduced a frameshift mutation into this region of the duck hepatitis B virus (DHBV) genome and examined the phenotype of this mutant DNA by intrahepatic inoculation into newborn ducklings. Animals receiving mutant DNA developed DHBV infection, as judged by the presence in hepatocytes of characteristic viral replicative intermediates; molecular cloning and DNA sequencing confirmed that the original mutation was present in the progeny genomes. Infection could be efficiently transmitted to susceptible ducklings by percutaneous inoculation with serum from mutant-infected animals, indicating that infectious progeny virus was generated. These findings indicate that expression of the precore region of DHBV is not essential for genomic replication, core particle morphogenesis, or intrahepatic viral spread.