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Journal of Virology, November 1998, p. 8913-8920, Vol. 72, No. 11
Center for Agricultural Biotechnology,
University of Maryland Biotechnology Institute, and
Virginia-Maryland Regional College of Veterinary Medicine,
University of Maryland, College Park, Maryland 20742
Received 23 April 1998/Accepted 4 August 1998
We developed a reverse genetics system for infectious pancreatic
necrosis virus (IPNV), a prototype virus of the
Birnaviridae family, with the use of plus-stranded RNA
transcripts derived from cloned cDNA. Full-length cDNA clones of the
IPNV genome that contained the entire coding and noncoding regions of
RNA segments A and B were constructed. Segment A encodes a 106-kDa
precursor protein which is cleaved to yield mature VP2, nonstructural
protease, and VP3 proteins, whereas segment B encodes the RNA-dependent RNA polymerase VP1. Plus-sense RNA transcripts of both segments were
prepared by in vitro transcription of linearized plasmids with T7
RNA polymerase. Transfection of chinook salmon embryo (CHSE) cells with
combined transcripts of segments A and B generated infectious IPNV
particles 10 days posttransfection. Furthermore, a
transfectant virus containing a genetically tagged sequence was
generated to confirm the feasibility of this system. The presence and
specificity of the recovered virus were ascertained by
immunofluorescence staining of infected CHSE cells with rabbit
anti-IPNV serum and by nucleotide sequence analysis. In addition,
3'-terminal sequence analysis of RNA from the recovered
virus showed that extraneous nucleotides synthesized at the 3' end
during in vitro transcription were precisely trimmed or excluded during
replication, and hence these were not incorporated into the genome. An
attempt was made to determine if RNA-dependent RNA polymerase of IPNV
and infectious bursal disease virus (IBDV), another birnavirus, can
support virus rescue in heterologous combinations. Thus, CHSE cells
were transfected with transcripts derived from IPNV segment A and IBDV
segment B and Vero cells were transfected with transcripts derived from IBDV segment A and IPNV segment B. In either case, no infectious IPNV or IBDV particles were generated even after a third passage in
cell culture, suggesting that viral RNA-dependent RNA polymerase is
species specific. However, the reverse genetics system for IPNV
that we developed will greatly facilitate studies of viral replication
and pathogenesis and the design of a new generation of live attenuated
vaccines.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Generation of Infectious Pancreatic Necrosis Virus
from Cloned cDNA
*
Corresponding author. Mailing address: Center for
Agricultural Biotechnology, 6126 Plant Sciences Building, University of Maryland, College Park, Maryland 20742. Phone: (301) 405-4777. Fax:
(301) 314-9075. E-mail: vakharia{at}umbi.umd.edu.
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