CLONING AND ANALYSIS OF THE SACCHAROMYCES-CEREVISIAE MNN9 AND MNN1 GENES REQUIRED FOR COMPLEX GLYCOSYLATION OF SECRETED PROTEINS

Proteins secreted by the yeast Saccharomyces cerevisiae are usually mo dified by the addition at asparagine-linked glycosylation sites of lar ge heterogeneous mannan units that are highly immunogenic. Secreted pr oteins from mnn1 mnn9 mutant strains, in contrast, have homogeneous Ma n10GlcNAC2 oligosaccharides that lack the immunogenic alpha1,3-mannose linkages. We have cloned and sequenced the MNN9 and MNN1 genes, both of which encode proteins with the characteristics of type II membrane proteins. Mnn9p is a membrane-associated protein with unknown function that is required for the addition of the long alpha 1,6-mannose backb one of the complex mannan, whereas Mnn1p is most likely the alpha1,3-m annosyltransferase located in the Golgi apparatus.