DPM2 regulates the biosynthesis of dolichol phosphate-mannose. Dolichol-phosphate mannose (Dol-P-Man) serves as a donor of mannosyl residues on the lumenal side of the endoplasmic reticulum (ER). Lack of Dol-P-Man results in defective surface expression of GPI-anchored proteins. Dol-P-Man is synthesized from GDP-mannose and dolichol-phosphate on the cytosolic side of the ER by the enzyme dolichyl-phosphate mannosyltransferase. The protein encoded by DPM2 is a hydrophobic protein that contains 2 predicted transmembrane domains and a putative ER localization signal near the C terminus. This protein associates with DPM1 in vivo and is required for the ER localization and stable expression of DPM1 and also enhances the binding of dolichol-phosphate to DPM1.