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J. Virol. doi:10.1128/JVI.02721-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Formation of Hepatitis B Virus Covalently Closed Circular DNA: Removal of Genome-linked Protein

Department of Microbiology and Immunology, The Pennsylvania State University College of Medicine, Hershey, PA 17033

^* To whom correspondence should be addressed. Email: juh13{at}psu.edu.

	Abstract

Hepatitis B virus (HBV) contains a small, partially double-stranded, relaxed circular (RC) DNA genome. RC DNA needs to be converted to the covalently closed circular (CCC) DNA, which serves as the template for all viral RNA transcription. As a first step toward understanding how CCC DNA is formed, we have begun to analyze the viral and host factors that may be involved in CCC DNA formation, using transient and stable DNA transfections of HBV and the related avian hepadnavirus, the duck hepatitis B virus (DHBV). Our results showed that HBV CCC DNA formed in hepatoma cells was derived predominantly from RC DNA with precise junction sequence. In contrast to DHBV, HBV CCC DNA formation in cultured cells was accompanied by the accumulation of a RC DNA species from which the covalently attached viral reverse transcriptase (RT) protein was removed (protein-free or PF-RC DNA). Furthermore, whereas envelope-deficiency led to increased CCC DNA formation in DHBV, it resulted mainly in increased PF-RC, but not CCC, DNA in HBV, suggesting that the envelope protein(s) may negatively regulate a step in CCC DNA formation preceding deproteination in both HBV and DHBV. Interestingly, PF-RC DNA, in contrast to the RT-linked RC DNA, contained almost exclusively mature plus strand DNA, suggesting that the RT protein was removed preferentially from the mature RC DNA.

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