CLASSICAL SWINE FEVER VIRUS - RECOVERY OF INFECTIOUS VIRUSES FROM CDNA CONSTRUCTS AND GENERATION OF RECOMBINANT CYTOPATHOGENIC DEFECTIVE INTERFERING PARTICLES

The 5'- and 3'-terminal sequences of the genomic RNA from classical sw ine fever virus (CSFV) were determined, and the resulting information was used for construction of full-length CSFV cDNA clones. After trans fection of in vitro-transcribed RNA derived from a cDNA construct, inf ectious CSFV was recovered from porcine cells, To confirm the de novo generation of infectious CSFV from cloned DNA, a genetically tagged CS FV was constructed. In comparison with parental CSFV, the recombinant viruses were retarded in growth by about 1 order of magnitude. Introdu ction of a deletion by exchange of part of the full-length construct f or corresponding cDNA fragments derived from the genomes of cytopathog enic CSFV defective interfering particles (DIs) (G. Meyers and H.-J. T hiel, J. Virol, 69:3683-3689, 1995) resulted in recovery of cytopathog enic DIs from in vitro-transcribed RNA. This finding confirmed the hyp othesis that the deletion previously identified in the DI genomes is r esponsible for their cytopathogenicity, The established system will al low novel approaches to analysis of pestiviral molecular biology and i n particular to elucidation of the molecular basis of attenuation and cytopathogenicity of these viruses.