Part of the glycosylphosphatidylinositol-N- acetylglucosaminyltransferase (GPI-GnT) complex that catalyzes the transfer of N-acetylglucosamine from UDP-N-acetylglucosamine to phosphatidylinositol and participates in the first step of GPI biosynthesis (PubMed:16162815). May act by regulating the catalytic subunit PIGA (PubMed:16162815). . This is the function of Ensembl gene identifier ENSG00000255072 (PIGY, phosphatidylinositol glycan anchor biosynthesis class Y).