Glycosylphosphatidylinositol (GPI) represents an important anchoring molecule for cell surface proteins. The first step in its synthesis is the transfer of N-acetylglucosamine (GlcNAc) from UDP-N-acetylglucosamine to phosphatidylinositol (PI). This chemically simple step is genetically complex because three or four genes are required in both Saccharomyces cerevisiae (GPI1, GPI2 and GPI3) and mammals (GPI1, PIG A, PIG H and PIG C), respectively [].This entry includes the mammalian Phosphatidylinositol N-acetylglucosaminyltransferase subunit Q (PigQ), its homologue Phosphatidylinositol N-acetylglucosaminyltransferase subunit GPI1 (Gpi1) from yeast, and similar eukaryotic proteins. PigQ stabilises the complex of PIG-A, PIG-H, and PIG-C. It is important for the activity of this protein complex but not essential []. A similar function has been suggested for the yeast Gpi1 [].
