A HOMOLOG OF SACCHAROMYCES-CEREVISIAE DPM1P IS NOT SUFFICIENT FOR SYNTHESIS OF DOLICHOL-PHOSPHATE-MANNOSE IN MAMMALIAN-CELLS

Dolichol-phosphate-mannose (Dol-P-Man) serves as a donor of mannosyl r esidues in major eukaryotic glycoconjugates, It donates four mannosyl residues in the N-linked oligosaccharide precursor and all three manno syl residues in the core of the glycosylphosphatidylinositol anchor, I n yeasts it also donates one mannose to the O-linked oligosaccharide. The yeast DPM1 gene encodes a Dol-P-Man synthase that is a transmembra ne protein expressed in the endoplasmic reticulum, We cloned human and mouse homologues of DPM1, termed hDPM1 and mDPM1, respectively, both of which encode proteins of 260 amino acids, having 30% amino acid ide ntity with yeast Dpm1 protein but lacking a hydrophobic transmembrane domain, which exists in the yeast synthase, Human and mouse DPM1 cDNA restored Dol-P-Man synthesis in mouse Thy-1-deficient mutant class E c ells, Mouse class E mutant cells had an inactivating mutation in the m DPM1 gene, indicating that mDPM1 is the gene for class E mutant, In co ntrast, hDPM1 and mDPM1 cDNA did not complement another Dol-P-Man synt hesis mutant, hamster Lec15 cells, whereas yeast DPM1 restored both mu tants, Therefore, in contrast to yeast, mammalian cells require hDPM1/ mDPM1 protein and a product of another gene that is defective in Lec15 mutant cells for synthesis of Dol-P-Man.