Transcripts and the putative RNA pregenome of duck hepatitis B virus: implications for reverse transcription.

Duck hepatitis B virus (DHBV) is a DNA virus that replicates by reverse transcription. We have examined transcripts of DHBV to elucidate mechanisms of gene expression and replication. Three major transcripts were characterized and related to the expression of the genes for the core antigen (DHBcAg), the surface antigen (DHBsAg), and the pre-S/DHBs protein, respectively. They are unspliced and overlap partially since they start at different promoter sites, but they terminate near a common polyadenylation signal. The messenger RNA related to DHBcAg expression is the only major transcript of more than genome length and therefore also represents the putative template for reverse transcription (pregenome). Its structure predicts a strategy of replication of hepatitis B viruses different from that of retroviruses.