The present invention provides genetically engineered strains of methylotrophic yeast including Pichia and especially Pichia pastoris capable of producing proteins with reduced or modified glycosylation. Methods of producing glycoproteins with reduced and/or modified glycosylation using such genetically engineered strains of Pichia are also provided. Vectors, which comprise coding sequences for null-1,2-mannosidase I, glucosidase II, GlcNAc-tranferase I and mannosidase II or comprising OCH1 disrupting sequence, for transforming methylotrophic yeasts are contemplated by the present invention. Kit for providing the comtemplated vectors are also included in this invention.