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J Virol, August 1998, p. 6785-6795, Vol. 72, No. 8
Liver Diseases Section, National Institute of
Diabetes and Digestive and Kidney Diseases, National Institutes of
Health, Bethesda, Maryland 20892
Received 20 February 1998/Accepted 6 May 1998
Functional analysis of naturally occurring hepatitis B virus (HBV)
mutations is crucial in understanding their impact on disease. We have
recently identified two mutations in the HBV core promoter of an HBV
strain associated with fulminant hepatitis leading to highly (15-fold)
enhanced replication as a result of increased viral encapsidation of
pregenomic RNA into the core particles (T. F. Baumert et al.,
J. Clin. Invest. 98:2268-2276, 1996). Functional studies in an
encapsidation assay had demonstrated that the increase in encapsidation
was largely independent of pregenomic RNA transcription. In this study,
we define the molecular mechanism whereby the two core promoter
mutations (C to T at nucleotide [nt] 1768 and T to A at nt 1770)
result in enhanced viral encapsidation and replication. The effect of
these mutations leading to increased encapsidation is mediated through
enhanced core protein synthesis (15-fold) by the mutant virus. The
marked increase in core protein synthesis is largely a result of
posttranscriptional or translational effect of the mutations because
the mutations resulted in only a twofold increase in pregenomic RNA
transcription. In addition, this effect appears to be selective for
core expression since reverse transcriptase-polymerase expression was
increased only twofold. trans-complementation analyses of
HBV replication demonstrated that enhanced replication occurred only
when the mutations were provided together with the core protein in
trans, confirming the functional association of the core
promoter mutations and core protein expression. In addition, the effect of the mutations appears to be quantitatively dependent on the strain
background to which the mutations were introduced. Our study suggests
that the HBV core promoter regulates core protein expression at both
transcriptional and posttranscriptional levels.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Naturally Occurring Mutations Define a Novel
Function of the Hepatitis B Virus Core Promoter in Core Protein
Expression
*
Corresponding author. Mailing address: Liver Diseases
Section, NIDDK-NIH, 10 Center Dr., Rm. 9B16, Bethesda, MD 20892-1800. Phone: (301) 496-1721. Fax: (301) 402-0491. E-mail:
jliang{at}nih.gov.
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