The hepatitis B virus-associated reverse transcriptase is encoded by the viral pol gene

We have used activity gel analysis and immunoblotting to provide evidence linking the hepatitis B virus (HBV) reverse transcriptase with its longest unassigned open reading frame (polymerase [Pol]-ORF). Activity gel analysis demonstrated that infectious HBV particles secreted by the Hep 2.2.15 cell line contain major (approximately 70 kilodaltons [kDa]) and minor (approximately 90 kDa) reverse transcriptase activities. By Western immunoblotting, we detected in both HBV particles and Hep 2.2.15 cell extract a approximately 70-kDa Pol-specific peptide. This approximately 70-kDa peptide reacted with antisera directed against the carboxy terminus of the pol gene product. No such immunoreactivity was observed with antisera against the amino terminus of the Pol peptide. The reverse transcriptase protein which was eluted from the major approximately 70-kDa region detected on an activity gel reacted with Pol-specific antisera. Furthermore, reverse transcriptase activity was immunoprecipitated from dissociated HBV particles by using Pol-specific antisera. On the basis of our results, we suggest that HBV encodes its reverse transcriptase from the Pol-ORF.