Changing the Site of Initiation of Plus-Strand DNA Synthesis Inhibits the Subsequent Template Switch during Replication of a Hepadnavirus

Unique to hepadnavirus reverse transcription is the process of primer translocation, in which the RNA primer for the initiation of plus-strand DNA synthesis is generated at one site on its template, DR1, and is moved to a new site, DR2. For duck hepatitis B virus (DHBV), DR2 is located within 50 nucleotides of the 5′ end of the minus-strand DNA template. When the synthesis of plus-strand DNA proceeds to the 5′ terminus of the minus strand, the 3′ end of the minus strand becomes the template for DNA synthesis. This switch in templates circularizes the nascent genome and is required for the genesis of the relaxed circular form of the DNA and the mature capsid. Maturation of the capsid is a prerequisite for virus egress. We have analyzed a series of DHBV variants in which plus-strand DNA synthesis was initiated from a new position relative to the 5′ end of the template. For these variants, the subsequent circularization was inhibited. We found that when the number of nucleotides between the site of initiation of plus-strand DNA synthesis and the 5′ end of its template was restored to 54 nucleotides, circularization was substantially restored. These results mean that the process of circularization is influenced by the earlier steps in DNA replication. This sensitivity is consistent with the notion that this region of the nascent genome is in a dynamic structure that is crucial for successful DNA replication.