Localization of viral proteins in cells infected with bovine viral diarrhoea virus

Bovine viral diarrhoea virus (BVDV) is a member of the genus Pestivirus wit hin the family Flaviviridae. In this report, protein localization studies w ere performed to assess the mechanism for the release of mature virus parti cles from infected cells. Since BVDV is an enveloped virus, budding from ei ther intra- or extracellular membranes is feasible. A prerequisite for the latter mechanism is the integration of viral glycoproteins into the host ce ll membrane. Using monoclonal antibodies (MAbs) directed against the viral envelope glycoproteins E2 and E-RNS, no specific signals were detected on t he surface of BVDV-infected cells by indirect fluorescence, confocal micros copy or fluorescence-activated cell sorter analyses. Furthermore, biotin-la belled cell surface proteins of virus-infected and non-infected cells were not detected by immunoprecipitation using MAbs directed against E-RNS and E 2 or the non-structural protein NS2-3. None of these proteins was detected on the cell surface. In addition, to analyse the intracellular localization of the two viral glycoproteins E-RNS and E2 and the non-structural protein s NS2-3 and NS3, subcellular fractionation of virus-infected cells followed by radioimmunoprecipitation with the MAbs were performed. These results le d to the conclusion that the BVDV envelope glycoproteins E-RNS and E2 as we ll as the nonstructural proteins NS2-3 and NS3 were almost quantitatively a ssociated with intracellular membranes. These findings indicate that BVDV i s released by budding into the cisternae of the endoplasmic reticulum and t hat there seems to be no correlation between the location and function of t he analysed proteins.