PRODUCTION OF FOREIGN PROTEINS IN THE YEAST PICHIA-PASTORIS

The methanol-utilizing yeast Pichia pastoris has been developed as a h ost system for the production of heterologous proteins of commercial i nterest. An industrial yeast selected for efficient growth on methanol for biomass generation, P. pastoris is readily grown on defined mediu m in continuous culture at high volume and density. A unique feature o f the expression system is the promoter employed to drive heterologous gene expression, which is derived from the methanol-regulated alcohol oxidase I gene (AOX1) of P, pastoris, one of the most efficient and t ightly regulated promoters known. The strength of the AOX1 promoter re sults in high expression levels in strains harboring only a single int egrated copy of a foreign-gene expression cassette. Levels may often b e further enhanced through the integration of multiple cassette copies into the P, pastoris genome and strategies to construct and select mu lticopy cassette strains have been devised. The system is particularly attractive for the secretion of foreign-gene products. Because P. pas toris endogenous protein secretion levels are low, foreign secreted pr oteins often appear to be virtually the only proteins in the culture b roth, a major advantage in processing and purification.