Biochemical and genetic evidence for the hepatitis B virus replication strategy.

Hepatitis B viruses synthesize their open circular DNA genomes by reverse transcription of an RNA intermediate. The details of this process have been examined with the use of mammalian hepatitis B viruses to map the sites for initiation and termination of DNA synthesis and to explore the consequences of mutations introduced at short, separated direct repeats (DR1 and DR2) implicated in the mechanisms of initiation. The first DNA strand to be synthesized is initiated within DR1, apparently by a protein primer, and the completed strand has a short terminal redundancy. In contrast, the second DNA strand begins with the sequence adjacent to DR2, but its 5' end is joined to an oligoribonucleotide that contains DR1; thus the putative RNA primer has been transposed to the position of DR2. It is now possible to propose a detailed strategy for reverse transcription by hepatitis B viruses that can be instructively compared with that used by retroviruses.