Dolichyl-phosphate-mannose (DPM, DOLPman) is the donor of mannose groups in the synthesis of the dolichyl pyrophosphate-linked precursor oligosaccharide in asparagine-linked glycosylation, in the synthesis of the glycosyl phosphatidylinositol (GPI) anchor precursor, in protein O-mannosylation and in protein C-mannosylation. Its synthesis proceeds in two steps. First, cytosolic GDP-mannose reacts with dolichyl phosphate exposed on the cytosolic face of the endoplasmic reticulum membrane to form DPM with its mannose moiety oriented toward the cytosol. The DPM molecule then flips in the endoplasmic reticulum membrane, so that its mannose moiety is in the endoplasmic reticulum lumen, accessible to the enzymes that catalyze its transfer to growing glycolipids and glycoproteins (Kinoshita and Inoue, 2000; Maeda et al, 2000).