EFFECT OF TUNICAMYCIN AND MONENSIN ON THE TRANSPORT TO THE CELL-SURFACE AND SECRETION OF A VIRAL MEMBRANE GLYCOPROTEIN CONTAINING BOTH N-LINKED AND O-LINKED SUGARS

Most membrane glycoproteins contain either N-linked or O-linked oligos accharides, which play important roles in comet folding, stability, an d intracellular transport. Some glycoproteins, however, contain both t he N- and O-linked sugars. To study the roles of the two types of glyc osylation in intracellular transport we have used as a model the glyco protein gC-1 of herpes simplex virus type 1 (HSV-1), which contains bo th N- and O-linked oligosaccharides. Cloned gene of gC-1 was expressed constitutively in mammalian cells to produce the gC-1 glycoprotein co ntaining both types of glycosylation. Only a fraction of the gC-1 glyc oprotein was secreted into the medium. Addition of tunicamycin blocked N-golycosylation and the gC-1 protein of reduced size containing only O-linked sugars was formed. This O-glycosylated gC-1 protein was tran sported to the cell surface and secreted into the medium, indicating t hat glycoprotein transport to and across the cell surface occurs in th e absence of N-glycans. The data suggest either that O-glycans may con tribute to this process or that transport can occur in the absence of both N- and O-glycans.