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J Virol, April 1998, p. 2806-2814, Vol. 72, No. 4
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Genotype-Specific Complementation of Hepatitis
Delta Virus RNA Replication by Hepatitis Delta Antigen
John L.
Casey* and
John L.
Gerin
Division of Molecular Virology and
Immunology, Georgetown University Medical Center, Rockville, Maryland
20852
Received 23 July 1997/Accepted 16 December 1997
Characterizations of genetic variations among hepatitis delta virus
(HDV) isolates have focused principally on phylogenetic analysis of
sequences, which vary by 30 to 40% among three genotypes and about 10 to 15% among isolates of the same genotype. The significance of the
sequence differences has been unclear but could be responsible for
pathogenic variations associated with the different genotypes. Studies
of the mechanisms of HDV replication have been limited to cDNA clones
from HDV genotype I, which is the most common. To perform a comparative
analysis of HDV RNA replication in genotypes I and III, we have
obtained a full-length cDNA clone from an HDV genotype III isolate. In
transfected Huh-7 cells, the functional roles of the two forms of the
viral protein, hepatitis delta antigen (HDAg), in HDV RNA replication
are similar for both genotypes I and III; the short form is required
for RNA replication, while the long form inhibits replication. For both
genotypes, HDAg was able to support replication of RNAs of the same
genotype that were mutated so as to be defective for HDAg production.
Surprisingly, however, neither genotype I nor genotype III HDAg was
able to support replication of such mutated RNAs of the other genotype. The inability of genotype III HDAg to support replication of genotype I
RNA could have been due to a weak interaction between the RNA and HDAg.
The clear genotype-specific activity of HDAg in supporting HDV RNA
replication confirms the original categorization of HDV sequences in
three genotypes and further suggests that these should be referred to
as types (i.e., HDV-I and HDV-III) rather than genotypes.
*
Corresponding author. Mailing address: Division of
Molecular Virology and Immunology, Georgetown University Medical
Center, 5640 Fishers Lane, Rockville, MD 20852. Phone: (301) 881-2676. Fax: (301) 881-0810. E-mail:
caseyj{at}medlib.georgetown.edu.
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