Inactivation of the RNase Activity of Glycoprotein Erns of Classical Swine Fever Virus Results in a Cytopathogenic Virus

AUTOR(ES)

Hulst, M. M.

FONTE

American Society for Microbiology

RESUMO

Envelope glycoprotein Erns 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 Erns 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 Erns was inserted into the p10 locus of a baculovirus vector and expressed in insect cells. Compared to intact Erns, the mutated proteins had lost their RNase activity. The mutated proteins reacted with Erns-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 Erns. 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 Erns (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 Erns gene and by neutralizing polyclonal antibodies directed against Erns, 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 Erns 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.

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