An alternative −1/+2 open reading frame exists within viral Npro(1-19) region of bovine viral diarrhea virus SD-1

We previously reported the engineering of an Npro-disrupted bovine viral diarrhea virus (BVDV), BSD1-Npro/eGFP2A (Fan and Bird, 2008a). Here, we report that BSD1-Npro/eGFP2A survives a single nucleotide missing in its C-terminal eGFP region. By using our established reverse genetics system for BVDV, we confirm that the viral mutant is rescued through a −1/+2 ORF initiated in the Npro(1-19)/eGFP region of the mutant viral genome. We furthermore uncover that this event occurs in the Npro(1-19) region of BVDV strain SD-1. The rescued viral mutant showed dramatic reductions in levels of both viral RNA and viral protein in host cells. Although the mutant is similar to the native strain in viral kinetics, the peak yield of the mutant is decreased dramatically. These findings reveal the existence of an alternative −1/+2 ORF in the Npro(1-19) region during the replication of BVDV and open a new avenue to understand the life cycle and pathogenesis of pestiviruses.