ABSTRACT: The genus Pestivirus of the family Flaviviridae comprises three established species, namely, bovine viral diarrhea virus (BVDV), classical swine fever virus (CSFV), and border disease virus from sheep (BDV). In this study, we report the first complete nucleotide sequence of BDV, that of strain X818. The genome is 12,333 nucleotides long and contains one long open reading frame encoding 3, 895 amino acids. The 5' noncoding region (NCR) of BDV X818 consists of 372 nucleotides and is thus similar in length to the 5' NCR reported for other pestiviruses. The 3' NCR of X818 is 273 nucleotides long and thereby at least 32 nucleotides longer than the 3' NCR of pestiviruses analyzed thus far. Within the 3' NCR of BDV X818, the sequence motif TATTTATTTA was identified at four locations. The same repeat was found at two or three locations within the 3' NCR of different CSFV isolates but was absent in the 3' NCR of BVDV. Analysis of five additional BDV strains showed that the 3' NCR sequences are highly conserved within this species. Comparison of the deduced amino acid sequence of X818 with the ones of other pestiviruses allowed the prediction of polyprotein cleavage sites which were conserved with regard to the structural proteins. It has been reported for two BVDV strains that cleavage at the nonstructural (NS) protein sites 3/4A, 4A/4B, 4B/5A, and 5A/5B is mediated by the NS3 serine protease and for each site a conserved leucine was found at the P1 position followed by either serine or alanine at P1' (N. Tautz, K. Elbers, D. Stoll, G. Meyers, and H.-J. Thiel, J. Virol. 71:5415-5422, 1997; J. Xu, E. Mendez, P. R. Caron, C. Lin, M. A. Murcko, M. S. Collett, and C. M. Rice, J. Virol. 71:5312-5322). Interestingly, P1' of the predicted NS5A/5B cleavage site of BDV is represented by an asparagine residue. Transient expression studies demonstrated that this unusual NS5A/5B processing site is efficiently cleaved by the NS3 serine protease of BDV.
