Abstract: A method for making a chitosan product from yeast cells is disclosed herein. Yeast cells are cultured to form a biomass of yeast cells. The yeast cells are induced to undergo meiosis causing the yeast cells to form asci containing ascospores wherein each ascospore contains a chitosan protective layer in the ascospore wall. Chitosan is extracted from the ascospores, purified to form purified chitosan, and precipitated and dried to form a chitosan product.

Abstract: Novel promoters which are derived from P. pastoris pastoris which are inducible or repressible under specific growth conditions are provided. These promoters are useful for regulating the expression of a desired structural gene, e.g., a mammalian polypeptide. Particularly preferred is the use of these novel promoters to regulate gene expression in polyploidal yeast such as diploidal P. pastoris produced by mating or spheroplast fusion.

Abstract: Methods are provided for the synthesis and secretion of recombinant proteins preferably large mammalian proteins or hetero-multimeric proteins at high levels and for prolonged time in polyploid, preferably diploid yeast. These methods use various mating competent yeast, including Pichia. In a preferred embodiment, a first expression vector is transformed into a first haploid cell; and a second expression vector is transformed into a second haploid cell. The transformed haploid cells, each individually synthesizing a non-identical polypeptide, are identified and then genetically crossed or fused. The resulting diploid strains are utilized to produce and secrete fully assembled and biologically functional hetero-multimeric protein.