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Description: 1. Field of the Invention This invention relates to the characterization of the role that glycosylation of the transmembrane glycoprotein E1 of highly virulent Classical Swine Fever Virus (CSFV) strain Brescia plays during infection in the natural host and to theutilization of a strategy for manipulating the pattern of glycosylation for particular E1 glycosylation sites in order to alter CSFV virulence, providing a useful tool in the design and development of CSF live-attenuated vaccines. 2. Description of the Relevant Art Classical swine fever (CSF) is a highly contagious disease of swine. The etiological agent, CSF virus (CSFV), is a small, enveloped virus with a positive, single-stranded RNA genome and, along with Bovine Viral Diarrhea Virus (BVDV) and BorderDisease Virus (BDV), is classified as a member of the genus Pestivirus within the family Flaviridae (Becher et al. 2003. Virology 311: 96-104). The 12.5 kb CSFV genome contains a single open reading frame that encodes a 3898-amino-acid polyprotein andultimately yields 11 to 12 final cleavage products (NH.sub.2--Npro-C-E.sup.rns-E1-E2-p7-NS2-NS3-NS4A-NS4B--NS5A-NS5B--COOH) through co- and post-translational processing of the polyprotein by cellular and viral proteases (Rice, C. M. 1996. In:Fundamental Virology, 3rd edition, Knipe et al., eds., Lippincott Raven, Philadelphia, Pa., pages 931-959). Structural components of the CSFV virion include the capsid (C) protein and glycoproteins E.sup.rns, E1, and E2. E1 and E2 are anchored to theenvelope at their carboxyl termini and Ems loosely associates with the viral envelope (Slater-Handshy et al. 2004. Virology 319: 36-48; Weiland et al. 1990. J. Virol. 64: 3563-3569; Weiland et al. 1999. J. Gen. Virol. 80: 1157-1165). E1 and E2 aretype I transmembrane proteins with an N-terminal ectodomain and a C-terminal hydrophobic anchor (Thiel et al. 1991. J. Virol. 65: 4705-4712). E1 has been implicated (Wang et al. 2004. Virology 330: 332-341), along wit