Effects of N-Glycosylation and Inositol on the ER Stress Response in YeastSaccharomyces cerevisiae

Abstract

IRE1 and HAC1 are essential for the unfolded protein response in the endoplasmic reticulum (ER). IRE1- and HAC1-disruptants require high concentrations of inositol for its normal growth. The ALG6, ALG8, and ALG10 genes encode the glucosyltransferases necessary for the completion of the synthesis of the lipid-linked oligosaccharide used for the asparagine-linked glycosylation of proteins in that order. Here we show that, given a combination of the hac1 defect with a disruption of ALG6, ALG8, and ALG10, no strains grow on inositol-free medium. However, the growth defect of the hac1-alg10 double disrupted was partially, but significantly, suppressed by the addition of inositol to the medium. These results indicate that inositol, according to the numbers of glucose residues in the oligosaccharide, plays an important role in the stress response and quality control of glycoproteins in the ER.