Attenuated Lapinized Chinese Strain of Classical Swine Fever Virus: Complete Nucleotide Sequence and Character of 3′-Noncoding Region

The complete nucleotide sequence including precise 5′- and 3′-terminal non-coding regions (NCRs) of the attenuated lapinized Chinese strain (HCLV) of Classical Swine Fever Virus (CSFV) was determined from overlapping cDNA clones constructed by separated RT-PCR and rapid amplification of cDNA ends (RACE) methods. The genomic RNA of the HCLV strain consists of 12,310 nucleotides (nts) including 374 nts and 242 nts in the 5′- and 3′-NCRs, respectively. It contains one large open reading frame (ORF) encoding a polyprotein of 3,898 amino acids with a calculated molecular weight of 437.6 kDa. There is one notable insertion of 12 continuous nts, CTTTTTTCTTTT in the 3′-NCR of HCLV genomic cDNA when compared with its parental virulent Shimen strain. Sequence alignment of partial 3′-NCR reveals two groups of CSFV vaccine strains carrying similar T-rich insertions at different positions in this region. Computer-predicted secondary structures suggest that T-rich insertion greatly change the structures and thus decrease the promoter functions of 3′-NCRs during the replications of these two groups of CSFV vaccine strains.