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J. Virol., 01 1997, 345-353, Vol 71, No. 1
PP Scaglioni, M Melegari and JR Wands
Hepadnaviruses encode two core-related open reading frames. One directs the
synthesis of the p21 core protein, which subsequently becomes a structural
component of the viral nucleocapsid. The other produces a p25 precore
protein that is targeted by a signal peptide to a cell secretory pathway
where N-terminal processing will create a p22 species. This molecule will
be further modified at the C-terminal region to generate p17, and the
truncated protein is secreted from the cell as hepatitis B e antigen
(HBeAg). The function of the precore gene in the biology of hepadnaviruses
is unknown. We found that ablation of the precore gene resulted in the
generation of a hepatitis B virus (HBV) species with a
high-replication-level phenotype. More important, expression in trans of
physiologic levels of p25 restored viral replication to wild-type levels.
Moreover, transient or stable overexpression of the precore gene resulted
in striking inhibition of HBV replication. The molecular species
responsible for this viral inhibitory effect was identified as the p22
nonsecreted HBeAg precursor protein. By sucrose gradient sedimentation
analysis, we determined that expression of p22 leads to the formation of
nucleocapsids similar to those made with wild-type p21 core protein.
Immunoprecipitation experiments revealed that the p21 and p22 physically
interact and form hybrid nucleocapsid structures devoid of pregenomic viral
RNA. These experiments suggest that expression of the precore gene may be
important in the regulation of HBV replication and describe a possible
molecular mechanism(s) for this effect.
Copyright © 1997, American Society for Microbiology
Posttranscriptional regulation of hepatitis B virus replication by the precore protein
Molecular Hepatology Laboratory, Massachusetts General Hospital Cancer Center, Harvard Medical School, Charlestown 02129, USA.
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