A SORTING MOTIF LOCALIZES THE FOAMY VIRUS GLYCOPROTEIN TO THE ENDOPLASMIC-RETICULUM

We recently identified an endoplasmic reticulum (ER) retrieval signal- the dilysine motif-in the glycoproteins of all five foamy viruses (FVs ) for which sequences were available (P. A. Goepfert, G. Wang, and M. J. Mulligan, Cell 82:543-544, 1995). In the present study, expression of recombinant human FV (HFV) glycoprotein and analyses of oligosaccha ride modifications and precursor cleavage indicated that the protein w as localized to the ER. HFV glycoproteins encoding seven different dil ysine motif mutations were then expressed. The results indicated that disruptions of the dilysine motif resulted in higher levels of forward transport of the HFV glycoprotein from the ER through the Golgi appar atus to the plasma membrane. We conclude that the dilysine moth is res ponsible for ER sorting of the FV glycoprotein. Signal-mediated ER loc alization has not previously been described for a retroviral glycoprot ein.