Regulates the biosynthesis of dolichol phosphate-mannose (PubMed:9724629). Regulatory subunit of the dolichol-phosphate mannose (DPM) synthase complex; essential for the ER localization and stable expression of DPM1 (PubMed:9724629). Part of the glycosylphosphatidylinositol-N-acetylglucosaminyltransferase (GPI-GnT) complex that catalyzes the transfer of N-acetylglucosamine from UDP-N-acetylglucosamine to phosphatidylinositol and participates in the first step of GPI biosynthesis. May act by regulating the GPI-GNT complex (By similarity). Protein modification; protein glycosylation. Component of the dolichol-phosphate mannose (DPM) synthase complex composed of DPM1, DPM2 and DPM3; in the complex interacts directly with DPM3 (PubMed:9724629). Component of the glycosylphosphatidylinositol-N-acetylglucosaminyltransferase (GPI-GnT) complex composed at least by PIGA, PIGC, PIGH, PIGP, PIGQ, PIGY and DPM2. Interacts with PIGA, PIGC and PIGQ (By similarity). Belongs to the DPM2 family.