Probable component of the GPI-GlcNAc transferase (GPI-GnT) complex in the endoplasmic reticulum, a complex that catalyzes transfer of GlcNAc from UDP-GlcNAc to an acceptor phosphatidylinositol, the first step in the production of GPI-anchors for cell surface proteins. Ras may inhibit the enzyme activity of the GPI-GnT complex via the association between ERI1 and RAS2. Glycolipid biosynthesis; glycosylphosphatidylinositol-anchor biosynthesis. Component of the phosphatidylinositol N-acetylglucosaminyltransferase (GPI-GlcNAc transferase) complex composed of at least GPI1, GPI2, GPI3, GPI15, GPI19 and ERI1 (Probable). Interacts with GPI2 (PubMed:15163411). Interacts with GTP-bound RAS2 in an effector loop-dependent manner (PubMed:12832483). Defects cause hyperactive Ras phenotypes, probably due to diminished GPI-anchor protein production.