Localization of the non-structural protein NS3 in bluetongue virus-infected cells

The localization of the blue tongue virus (BTV) non-structural proteins NS3 and NS3a has been identified using immunoelectron microscopical techniques. NS3 and NS3a have been observed in the plasma membrane of BTV- and recombinant vaccinia virus (expressing NS3)-infected cells. The NS3 protein was associated with areas of membrane perturbation. There was a good correlation between the presence of NS3 and NS3a and BTV release. The NS3 protein was associated with membrane fragments and the inability to detect it on the extracellular aspect of intact cells suggested that the protein was not exposed extracellularly. Electron microscopical and biochemical evidence suggested that fragments of plasma membrane containing NS3 and NS3a were released from infected cells. Collectively, the data indicate that NS3 and NS3a may be involved in the final stages of BTV morphogenesis, i.e. the release of BTV from infected cells.