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J Virol, April 1998, p. 2765-2776, Vol. 72, No. 4
Pharmaceutical Research Institute,
Bristol-Myers Squibb, Wallingford, Connecticut 06492
Received 15 September 1997/Accepted 6 January 1998
The double-stranded DNA genome of human hepatitis B virus (HBV) and
related hepadnaviruses is reverse transcribed from a pregenomic RNA by
a viral polymerase (Pol) harboring both priming and RNA- and
DNA-dependent elongation activities. Although hepadnavirus replication
occurs inside viral nucleocapsids, or cores, biochemical systems for
analyzing this reaction are currently limited to unencapsidated Pols
expressed in heterologous systems. Here, we describe cis and trans classes of replicative HBV cores, produced in the
recombinant baculovirus system via coexpression of HBV core and Pol
proteins from either a single RNA (i.e., in cis) or two
distinct RNAs (in trans). Upon isolation from insect cells,
cis and trans cores contained Pol-linked HBV
minus-strand DNA with 5' ends mapping to the authentic elongation
origin DR1 and also plus-strand DNA species. Only trans
cores, however, were highly active for the de novo priming and reverse
transcription of authentic HBV minus strands in in vitro endogenous
polymerase assays. This reaction strictly required HBV Pol but not the
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Generation of Replication-Competent Hepatitis B
Virus Nucleocapsids in Insect Cells
stem-loop element, although the presence of one
, or better, two
s, enhanced minus-strand synthesis up to 10-fold. Compared to
unencapsidated Pol enzymes, encapsidated Pol appeared to be (i) highly
processive, able to extend minus-strand DNAs of 400 nucleotides from
DR1 in vitro, and (ii) more active for HBV plus-strand synthesis. These
observations suggest possible contributions to the replication process
from the HBV core protein. These novel core reagents should facilitate the analysis of HBV replication in its natural environment, the interior of the capsid, and also fuel the development of new anti-HBV drug screens.
*
Corresponding author. Mailing address: Pharmaceutical
Research Institute, Bristol-Myers Squibb, 5 Research Parkway,
Wallingford, CT 06492. Phone: (203) 284-7573. Fax: (203) 284-6088. E-mail: David_N._Standring{at}ccmail.BMS.com.
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