The infection of domesticated swine and ruminants by members of the Pestivirus genus of the Flaviviridae family

members of the Pestivirus genus of the Flaviviridae family causes significant economic losses worldwide to the agricultural industry (Theil et al., 1996). Bovine viral diarrhoea virus (BVDV) has served as the prototype species for this genus, as well as a surrogate virus for hepatitis C virus drug development (Baginski et al., 2000; Bukhtiyarova et al., 2002). BVDV, a positive single-stranded RNA virus, has a genome of approximately 12600 nucleotides that consists of a single open reading frame flanked by 5′ and 3′ untranslated regions. The structural genes are clustered at the 5′ end of the genome and make up one-third of the coding sequence; the nonstructural genes are located at the 3′ end of the genome and make up two-thirds of the coding sequence (Collett et al., 1988, 1991). The open reading frame encodes a single polypeptide that is coand posttranslationally processed by cellular and viral enzymes into at least nine viral proteins. The BVDV non-structural proteins consist of NS2NS3, NS3, NS4A, NS4B, NS5A and NS5B. NS2-3 and NS3 are multifunctional proteins that contain protease, RNA binding, NTPase and helicase functions (Grassmann et al., 1999). The NS2-NS3 protease is responsible for the cleavage between NS2-NS3, whereas NS3 protease cleaves between NS3-NS4A, NS4A-NS4B, NS4B-NS5A and NS5A-NS5B. NS4A acts as a cofactor for the NS3 serine protease and increases the efficiency of several of these cleavage reactions (Tautz et al., 2000). NS5B is the RNAdependent RNA polymerase (RdRp; Kao et al., 1999; Lai et al., 1999; Steffens et al., 1999). The functions of the BVDV NS4B and NS5A have yet to be elucidated. In light of the lack of a cell-based system that models the entire hepatitis C virus (HCV) replication cycle, comparative studies between HCV and BVDV have validated the use of BVDV as a surrogate for HCV in the drug discovery process. Here we describe a potent, low-molecular weight compound that inhibits the replication of BVDV by interfering with the ability of the RdRp to initiate RNA synthesis. Moreover, we also describe BVDV variants that contain altered nucleotide sequences in their coding sequences for the RdRp and are resistant to the antiviral effects of this compound. Antiviral Chemistry & Chemotherapy 13:315–323