Required for proper folding and/or the stability of a subset of proteins in the endoplasmic reticulum. Aids the autocatalytic processing of PRB1. Component of glycosylphosphatidylinositol-mannosyltransferase 1 which transfers the first of the 4 mannoses in the GPI-anchor precursors during GPI-anchor biosynthesis. Probably acts by stabilizing the mannosyltransferase GPI14. Glycolipid biosynthesis; glycosylphosphatidylinositol-anchor biosynthesis. N-glycosylated. Present with 4930 molecules/cell in log phase SD medium. Belongs to the PIGX family.