O-glycosylation of intact and truncated ribophorins in brefeldin A- treated cells: newly synthesized intact ribophorins are only transiently accessible to the relocated glycosyltransferases

To overexpress ribophorin I the rat ribophorin I eDNA was excised from the pGEMI vector (Harnlk-Ort et al., 1987) and ligated into the eukaryofic expression vector pMT2 (Kaufman, 1990) using standard procedures (Sambrook et al., 1989) . HeLa cells were transiently transfected with this construct by the calcium phosphate precipitation method (10-20/zg DNA per 100-ram dish) and the synthesis, modification, and stability of ribophorin I were analyzed at 50-75 h after transfection.