The function of ALG5 (ALG5 dolichyl-phosphate beta-glucosyltransferase, Ensembl gene identifier ENSG00000120697) is as follows. Dolichyl-phosphate beta-glucosyltransferase that operates in the biosynthetic pathway of dolichol-linked oligosaccharides, the glycan precursors employed in protein asparagine (N)-glycosylation. The assembly of dolichol-linked oligosaccharides begins on the cytosolic side of the endoplasmic reticulum membrane and finishes in its lumen. The sequential addition of sugars to dolichol pyrophosphate produces dolichol-linked oligosaccharides containing fourteen sugars, including two GlcNAcs, nine mannoses and three glucoses. Once assembled, the oligosaccharide is transferred from the lipid to nascent proteins by oligosaccharyltransferases. Dolichyl-phosphate beta-glucosyltransferase produces dolichyl beta-D-glucosyl phosphate/Dol-P-Glc, the glucose donor substrate used sequentially by ALG6, ALG8 and ALG10 to add glucose residues on top of the Man(9)GlcNAc(2)-PP-Dol structure. These are the three last steps in the biosynthetic pathway of dolichol-linked oligosaccharides to produce Glc(3)Man(9)GlcNAc(2)-PP-Dol. The enzyme is most probably active on the cytoplasmic side of the endoplasmic reticulum while its product Dol-P-Glc is the substrate for ALG6, ALG8 and ALG11 in the lumen of the endoplasmic reticulum. .