The extra 16-amino-acid peptide at C-terminal NS2 of the hypervirulent type-2 bovine viral diarrhea viruses has no effect on viral replication and NS2-3 processing of type-1 virus.

Bovine viral diarrhea virus (BVDV) is an economically important cattle pathogen with worldwide distribution. Besides the segregation of noncytopathic and cytopathic (CP) biotypes, BVDV exists as two genotypes. Both genotypes cause similar disease, and the majority of type-2 BVDV (BVDV-2) is no more virulent than type-1 viruses (BVDV-1). However, some BVDV-2 viruses are hypervirulent and causative reagents of a lethal disease called severe acute bovine viral diarrhea. Amino acid (aa) sequence analysis shows that the majority of hypervirulent BVDV-2 isolates contains an extra 16 aa peptide (-SSCPVPFDPSCHCNYF-) at C-terminal NS2 region. In this study, we investigated the flexibility of the corresponding NS2 region of BVDV-1 for tolerance of this peptide insertion and its effect on viral pathogenicity. Based on an infectious cDNA clone of BVDV-1 SD-1, a cDNA clone called pASD1-IN was constructed with insertion of the 16 aa peptide in the corresponding NS2 site. In vitro transcription and transfection of Madin-Darby bovine kidney (MDBK) cells resulted in the generation of infectious chimeric virus termed ASD1-IN. ASD1-IN does not show CP effect on MDBK cells and is similar to ASD1 in viral growth. Furthermore, ASD1-IN shows an NS2-3 processing pattern similar to ASD1. These results reveal that insertion of the 16 aa peptide at C-terminal NS2 of BVDV-1, at least for SD-1, has no effect on viral replication and NS2-3 processing in MDBK cells.