Localization to the Golgi complex of Uukuniemi virus glycoproteins G1 and G2 expressed from cloned cDNAs.

The membrane glycoproteins G1 and G2 of Uukuniemi virus, a bunyavirus, accumulate in the Golgi complex (GC) during virus infection. These proteins have therefore been considered to be good models for studying the intracellular transport to and retention in the GC. In this study, I have used indirect immunofluorescence to localize in COS cells the Uukuniemi virus glycoproteins G1 and G2 expressed together or separately from cloned cDNAs with use of simian virus 40-based vectors. When expressed together from the full-length cDNA, G1 and G2 were correctly translocated, processed, and targeted to the GC, indicating that the information for GC targeting resides in the proteins. When the proteins were expressed separately, G1 was transported to the GC and retained there. In contrast, G2 could not be detected in the GC but was most probably retained and finally degraded in the endoplasmic reticulum. However, in cells cotransfected with G1 and G2 cDNAs, the proteins could both again be found in the GC. These results suggest that G1 is a responsible for targeting to and retention of the Uukuniemi virus glycoproteins in the GC. G2 would thus accumulate in the GC by virtue of its binding to G1.