Npro of Bungowannah virus exhibits the same antagonistic function in the IFN induction pathway than that of other classical pestiviruses

Bungowannah virus is the most divergent atypical pestivirus that had been detected up to now, and does not fit into any of the four approved species: Bovine viral diarrhea virus type 1 (BVDV-1) and type 2 (BVDV-2), Classical swine fever virus (CSFV) and Border disease virus (BDV). However, the presence of Npro and Erns coding regions, which are unique to pestiviruses, provides clear evidence of a pestivirus. Nevertheless, the amino acid identity of Bungowannah virus Npro and BVDV-1 Npro (strain CP7) is only 51.5%. By using a BVDV-1 backbone, a novel chimeric construct was generated, in which the genomic region encoding the non-structural protein Npro was replaced by that of Bungowannah virus (CP7_Npro-Bungo). In vitro studies of CP7_Npro-Bungo revealed autonomous replication with the same efficacy as the BVDV backbone CP7 and infectious high-titer virus could be collected. In order to compare the ability of interferon (IFN) suppression, two reporter gene assays, specific for type-I IFN, were carried out. In virus-infected cells, no significant difference in blocking of IFN expression between the parental virus CP7, Bungowannah virus and the chimeric construct CP7_Npro-Bungo could be detected. In contrast, an Npro deletion mutant showed an impaired replication in bovine cells and a marked type-I IFN response.Taken together, our findings reveal the compatibility of non-structural protein Npro of atypical Bungowannah virus with a BVDV type 1 backbone and its characteristic feature as an inhibitor of type-I IFN induction with an inhibitor-activity comparable to other pestiviruses.