ABSTRACT
An important breakthrough was reached when Summers and Mason, studying duck hepatitis virus-infected liver, demonstrated that hepadnaviruses replicate by reverse transcription of RNA. This chapter suggests that hepadnaviruses are related to retroviruses because both virus families use a rare method of replication by reverse transcription of RNA possess homology in important nucleotide and amino acid sequences, and share unique features of genome organization. Sequence analysis indicates that the nucleocapsid and polymerase genes for Hepatitis B virus (HBV), cauliflower mosaic virus (CaMV) of plants, and most retroviruses are located in overlapping translation frames. Two highly conserved domains in hepadnavirus proteins share Nucleotide. One domain is located between the core and polymerase gene sequences, while the other domain is located at the amino terminus of the core gene. The protease-like sequence located at the amino terminus of the core gene sequence is analogous to the pseudoprotease genes of lentiviruses and vaccinia virus.
