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Journal of Virology, September 1999, p. 7787-7794, Vol. 73, No. 9
Institute of Virology and Immunoprophylaxis,
CH-3147 Mittelhäusern, Switzerland
Received 3 November 1998/Accepted 9 June 1999
To determine the minimal requirements for autonomous RNA
replication of classical swine fever virus (CSFV), genomes having in-frame deletions within the genes for structural and flanking nonstructural proteins were constructed, based on an infectious cDNA
clone of CSFV Alfort/187. RNA was transcribed in vitro from the
respective plasmids and transfected into SK-6 swine kidney cells. The
replication competence of the RNA was determined by immunostaining
transfected cells for CSFV NS3 protein and by analysis of cell extracts
for viral RNA, as well as protein synthesis at different times after
transfection. The genes encoding Npro, C, Erns,
E1, E2, p7, and NS2 proved to be dispensable for RNA replication, but
the efficiency of replication varied strongly between individual constructs. RNA replicons containing the complete NS2-NS3 gene persisted in transfected cells and continued to replicate without causing any obvious morphological or functional damage to the cells,
whereas genomes lacking the NS2 gene replicated more efficiently and
induced a cytopathic effect. These findings suggest that NS2, although
it is not essential for pestivirus RNA replication, has a regulatory
function therein. Both cytopathogenic and noncytopathogenic replicons
were packaged into virus particles provided in trans by a
cotransfected full-length helper virus genome.
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Cytopathogenic and Noncytopathogenic RNA Replicons
of Classical Swine Fever Virus

*
Corresponding author. Mailing address: Institute of
Virology and Immunoprophylaxis, CH-3147 Mittelhäusern,
Switzerland. Phone: 41 31 848 92 11. Fax: 41 31 848 92 22. E-mail:
jon-duri.tratschin{at}ivi.admin.ch.
Present address: Institute of Human Gene Therapy, The Wistar
Institute, Philadelphia, PA 19104-4268.
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