GCN4-based expression system (pGES): Translationally regulated yeast expression vectors

The expression of foreign proteins in Saccharomyces cerevisiae is a powerfu l tool for basic research and the biotechnological industry. In spite of th e potential of S. cerevisiae, only a few useful expression vectors have bee n developed for this yeast. These vectors are based on an increasing transc ription rate in combination with an increase in gene dosage. Most vectors a re maintained as plasmids, which forces growth of cultures on poor selectiv e media. Expression of the yeast Gcn4 protein is regulated at the translati onal level and increases strongly Lender amino acid starvation. Because und er these conditions protein synthesis in general ceases, it is conceivable that regulatory elements that control Gcn4 expression could support selecti ve expression of foreign genes. We cloned DNA fragments residing upstream f rom the GCN4 coding sequence (including the 5' UTR) and ligated them to a c DNA that encodes the human serum albumin (HSA) gene. These GCN4 regulatory, elements induced efficient HSA expression at the translational level under amino acid starvation. The GCN4/HSA cassette promoted efficient, inducible expression on either a multicopy or integrative plasmid. The integrated ca ssette induced a high level of HSA in dense cultures grown on rich media. T hus, the GCN4-based expression system (pGES) provides high protein quantiti es. pGES Is the first expression vector to be induced at the translational level.