Regulated secretion of MuGM-CSF in Saccharomyces cerevisiae via GAL1:MF alpha 1 prepro sequences

Murine granulocyte-macrophage colony-stimulating factor (GM-CSF) was expressed in Saccharomyces cerevisiae using a novel regulated secretion system. This system involves the fusion of the GAL1 upstream regulatory region to the signal sequence of the alpha mating pheromone, and the integration of this GAL1:MF alpha 1 prepro:MuGM-CSF construct into the yeast chromosome. These constructs were very stable under both selective and nonselective conditions: after 30 generations of growth no plasmid loss was observed. The expression and secretion of MuGM-CSF were analyzed by biological assays and Western blots of yeast culture medium and yeast cell extracts. Expression of MuGM-CSF was regulated by galactose induction. In addition, expression levels were proportional to the number of tandem copies of the gene inserted into the yeast chromosome.