Tomato spotted wilt virus glycoproteins exhibit trafficking and localization signals that are functional in mammalian cells

The glycoprotein precursor (G1/G2) gene of tomato spotted wilt virus (TSWV) was expressed in BHK cells using the Semliki Forest virus expression syste m. The results reveal that in this cell system, the precursor is efficientl y cleaved and the resulting G1 and G2 glycoproteins are transported from th e endoplasmic reticulum (ER) to the Golgi complex, where they are retained, a process that could be blocked by tunicamycin. Expression of G2 alone res ulted in transport to and retention in the Golgi complex, albeit less effic ient, suggesting that G2 contains a Golgi retention signal. G1 alone was re tained in the ER, irrespective of whether it contained the precursor's sign al sequence or its own N-terminal hydrophobic sequence. Coexpression of G1 and G2 from separate gene constructs resulted in rescue of efficient G1 tra nsport, as the proteins coaccumulated in the Golgi complex, indicating that their interaction is essential for proper targeting to this organelle. The results demonstrate that transport and targeting of the plant TSWV glycopr oteins in mammalian BHK cells are strikingly similar to those of animal-inf ecting bunyavirus glycoproteins in mammalian cells. The observations are li kely to reflect the dual tropism of TSWV, which replicates both in its plan t host and in its animal (thrips) vector.