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J. Virol., 09 1996, 5845-5851, Vol 70, No. 9
VE Buckwold, Z Xu, M Chen, TS Yen and JH Ou
The basal core promoter (BCP) of hepatitis B virus (HBV) controls the
transcription of both the precore RNA and the core RNA. The precore RNA
codes for the secreted e antigen, while the core RNA codes for the major
core protein and the DNA polymerase and also is the pregenomic RNA. The
double mutation of nucleotides 1762 and 1764 in the BCP from A and G to T
and A, respectively, is frequently observed in HBV sequences isolated from
chronic patients. Several papers have reported conflicting results
regarding whether this double mutation is important for e antigen
expression. In order to address this issue, we have introduced this double
mutation into the HBV genome and studied its effects on HBV gene expression
and replication. Our results indicate that the mutated BCP can no longer
bind a liver-enriched transcription factor(s) and that the transcription of
only precore RNA and, consequently, the expression of e antigen were
reduced. The reduction of precore gene expression was accompanied by an
increase in progeny virus production. This increase was found to occur at
or immediately prior to the encapsidation of the pregenomic RNA. Thus, the
results of our in vitro study resolve the discrepancy of previous clinical
observations and indicate that this double mutation suppresses but does not
abolish the e antigen phenotype. The implications of these findings in the
pathogenesis of HBV are discussed.
Copyright © 1996, American Society for Microbiology
Effects of a naturally occurring mutation in the hepatitis B virus basal core promoter on precore gene expression and viral replication
Department of Molecular Microbiology and Immunology, University of Southern California, School of Medicine, Los Angeles, California 90033, USA.
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