CLONING AND ANALYSIS OF THE MNN4 GENE REQUIRED FOR PHOSPHORYLATION OFN-LINKED OLIGOSACCHARIDES IN SACCHAROMYCES-CEREVISIAE

The Saccharomyces cerevisiae MNN4 gene, which is involved in mannosylp hosphate transfer from GDP-mannose to N-linked oligosaccharide, has be en cloned from a lambda phage containing a yeast chromosome XI DNA fra gment, The MNN4 ORF encodes a protein of 1178 amino acids, The deduced amino acid sequence shows a topology of type II membrane proteins and has a unique repeated sequence of lysine and glutamic acid at the C-t erminus, Disruption and overexpression of MNN4 led to a decrease and i ncrease, respectively, of the mannosylphosphate content in cell wall m annans prepared from both mnn4 and wild type strains. A dramatic decre ase of mannosylphosphate occurs in Delta mnn4 mutants. The results fro m genetic and biochemical experiments combine to suggest that Mnn4p is required to mediate mannosylphosphate transfer in both the core and o uter chain portions of N-linked oligosaccharides.