Glycosylphosphatidylinositol (GPI) anchoring of proteins is a conserved 
posttranslational modification in the endoplasmic reticulum (ER). Soon after GPI 
is attached, an acyl chain on the GPI inositol is removed by post-GPI attachment 
to proteins 1 (PGAP1), a GPI-inositol deacylase. This is crucial for switching 
GPI-anchored proteins (GPI-APs) from protein folding to transport states. We 
performed haploid genetic screens to identify factors regulating GPI-inositol 
deacylation, identifying seven genes. In particular, calnexin cycle impairment 
caused inefficient GPI-inositol deacylation. Calnexin was specifically 
associated with GPI-APs, dependent on N-glycan and GPI moieties, and assisted 
efficient GPI-inositol deacylation by PGAP1. Under chronic ER stress caused by 
misfolded GPI-APs, inositol-acylated GPI-APs were exposed on the cell surface. 
These results indicated that N-glycans participate in quality control and 
temporal ER retention of GPI-APs, ensuring their correct folding and GPI 
processing before exiting from the ER. Once the system is disrupted by ER 
stress, unprocessed GPI-APs become exposed on the cell surface.