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J. Virol., 01 1998, 151-157, Vol 72, No. 1
MM Hulst, FE Panoto, A Hoekman, HG van Gennip and RJ Moormann
Envelope glycoprotein E(rns) of classical swine fever virus (CSFV) has been
shown to contain RNase activity and is involved in virus infection. Two
short regions of amino acids in the sequence of E(rns) are responsible for
RNase activity. In both regions, histidine residues appear to be essential
for catalysis. They were replaced by lysine residues to inactivate the
RNase activity. The mutated sequence of E(rns) was inserted into the p10
locus of a baculovirus vector and expressed in insect cells. Compared to
intact E(rns), the mutated proteins had lost their RNase activity. The
mutated proteins reacted with E(rns)-specific neutralizing monoclonal and
polyclonal antibodies and were still able to inhibit infection of swine
kidney cells (SK6) with CSFV, but at a concentration higher than that
measured for intact E(rns). This result indicated that the conformation of
the mutated proteins was not severely affected by the inactivation. To
study the effect of these mutations on virus infection and replication, a
CSFV mutant with an inactivated E(rns) (FLc13) was generated with an
infectious DNA copy of CSFV strain C. The mutant virus showed the same
growth kinetics as the parent virus in cell culture. However, in contrast
to the parent virus, the RNase-negative virus induced a cytopathic effect
in swine kidney cells. This effect could be neutralized by rescue of the
inactivated E(rns) gene and by neutralizing polyclonal antibodies directed
against E(rns), indicating that this effect was an inherent property of the
RNase-negative virus. Analyses of cellular DNA of swine kidney cells showed
that the RNase- negative CSFV induced apoptosis. We conclude that the RNase
activity of envelope protein E(rns) plays an important role in the
replication of pestiviruses and speculate that this RNase activity might be
responsible for the persistence of these viruses in their natural host.
Copyright © 1998, American Society for Microbiology
Inactivation of the RNase activity of glycoprotein E(rns) of classical swine fever virus results in a cytopathogenic virus
Institute for Animal Science and Health (ID-DLO), Research Branch Houtribweg, Lelystad, The Netherlands.
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