The present invention relates to eukaryotic host cells having modified oligosaccharides which may be modified further by 
heterologous expression of a set of glycosyltransferases, 
sugar transporters and mannosidases to become host-strains for the production of mammalian, e.g., human therapeutic glycoproteins. The invention provides 
nucleic acid molecules and combinatorial libraries which can be used to successfully target and express mammalian enzymatic activities such as those involved in 
glycosylation to 
intracellular compartments in a eukaryotic host 
cell. The process provides an engineered host 
cell which can be used to express and target any desirable 
gene(s) involved in 
glycosylation. Host cells with modified oligosaccharides are created or selected. N-glycans made in the engineered host cells have a Man5GlcNAc2 core structure which may then be modified further by 
heterologous expression of one or more enzymes, e.g., glycosyltransferases, 
sugar transporters and mannosidases, to yield human-like glycoproteins. For the production of therapeutic proteins, this method may be adapted to engineer 
cell lines in which any desired 
glycosylation structure may be obtained.