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J. Virol., 02 1997, 1310-1316, Vol 71, No. 2
M Kann, A Bischof and WH Gerlich
Hepadnaviruses contain a DNA genome, but they replicate via an RNA
intermediate, synthesized by the cellular RNA polymerase II in the nucleus
of the infected cell. Thus, nuclear transport of the viral DNA is required
in the viral life cycle. Protein-free DNA is only poorly imported into the
nucleus, so one or more of the viral proteins must be involved in the
transport of the viral genome. In order to identify these viral proteins,
we purified woodchuck hepadnavirus (WHV) core particles from infected
woodchuck liver, isolated WHV DNA, and extracted the covalent complex of
viral polymerase from the particles using urea. Intact core particles, the
polymerase-DNA complex, or protein-free WHV DNA from core particles was
added to digitonin- permeabilized HuH-7 cells, in which the cytosol was
substituted by rabbit reticulocyte lysate (RRL) and an ATP-generating
system. The distribution of the viral genome was analyzed by
semiquantitative PCR or by hybridization in total nuclei, RRL, nuclear
membranes, and nucleoplasm. The polymerase-DNA complex was efficiently
transported into the nucleus, as indicated by the resistance of the
nucleus- associated DNA to a short-term treatment with DNase I of the
intact nuclei. The DNA within core particles stayed mainly in the cytosol
and remained protected against DNase I. A minor part of the encapsidated
DNA was bound to nuclei. It was protected against DNase I but became
accessible after disruption of the nuclei. Deproteinized viral DNA
completely remained in the cytosol. These data show that the viral
polymerase is probably sufficient for mediating the transport of a
hepadnavirus genome into the nucleus and that the viral core particles may
release the genome at the nuclear membrane.
Copyright © 1997, American Society for Microbiology
In vitro model for the nuclear transport of the hepadnavirus genome
Institute of Medical Virology, Justus-Liebig-University, Giessen, Federal Republic of Germany. michael.kann@viro.med.uni-giessen.de
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