Duck hepatitis B virus (DHBV), like all other hepadnaviruses, is a retroid virus that bears a small DNA genome and replicates this DNA genome via reverse transcription through an RNA intermediate called pregenomic RNA (pgRNA; 1 ). All hepadnaviruses encode a multifunctional polymerase (pol), which is a specialized reverse transcriptase (RT) and plays key roles in several different aspects of the viral life cycle (2 –5 ). Pol has an RNA- and DNA-directed DNA polymerase (i.e., RT) activity that is responsible for DNA genome replication, which also entails its intrinsic RNase H activity responsible for degrading the pgRNA as the pgRNA is being reverse transcribed into the first (minus) strand of the DNA genome. In addition to the RT and RNase H activities, which are shared with retroviral RTs, the hepadnavirus polymerase displays the unique ability to initiate DNA synthesis de novo using pol itself as a protein primer (protein priming) (6 –9 ).