Glycosylphosphatidylinositol (GPI) lipid anchoring is an important post-translational modification of proteins that takes place in the endoplasmic reticulum. The synthesis of GPI is initiated by GPI-N-acetylglucosaminyltransferase (GPI-GnT), a complex of proteins including PIG-A, PIG-H, PIG-C, GPI1, and DPM2. PIG-Y, the mammalian homolog to yeast Eri1p, is also thought to be involved in the biosynthesis of GPI. The PIG-Y gene encodes two proteins, one of which arises from leaky scanning of the mRNA. This antibody only detects isoform 1 of PIG-Y. Despite its predicted molecular weight, PIG-Y often migrates at 28-30 kDa in SDS-PAGE.