Synthesis and encapsidation of duck hepatitis B virus reverse transcriptase do not require formation of core-polymerase fusion proteins.

The expression strategy of the duck hepatitis B virus (DHBV) P gene, which is assumed to encode the viral reverse transcriptase, was investigated by mutational analysis. This study showed that P gene expression starts in the region where the P gene overlaps the viral core gene. However, in contrast to retroviral reverse transcriptases, which are expressed via gag-pol fusion protein intermediates, the DHBV P gene product was found to be synthesized starting at a P gene ATG codon. The resulting protein can complement polymerase-negative mutants in trans and can reverse transcribe viral pregenomic RNA that does not encode an active polymerase. These findings raise the question of how reverse transcription of cellular RNAs can be avoided in infected cells.