Stabilizer subunit of the dolichol-phosphate mannose (DPM) synthase complex; tethers catalytic subunit DPM1 to the endoplasmic reticulum. Protein modification; protein glycosylation. Component of the dolichol-phosphate mannose (DPM) synthase complex composed of DPM1, DPM2 and DPM3; within the complex, associates with DPM1 via its C-terminal domain and with DPM2 via its N-terminal portion. This interaction stabilizes DPM1 protein. Belongs to the DPM3 family.