GCN4-Based Expression System (pGES): Translationally Regulated Yeast Expression Vectors

Abstract

The expression of foreign proteins in Saccharomyces cerevisiae is a powerful tool for basic research and the biotechnological industry. In spite of the potential of S. cerevisiae, only a few useful expression vectors have been developed for this yeast. These vectors are based on an increasing transcription rate in combination with an increase in gene dosage. Most vectors are maintained as plasmids, which forces growth of cultures on poor selective media. Expression of the yeast Gcn4 protein is regulated at the translational level and increases strongly under amino acid starvation. Because under these conditions protein synthesis in general ceases, it is conceivable that regulatory elements that control Gcn4 expression could support selective expression of foreign genes. We cloned DNA fragments residing upstream from the GCN4 coding sequence (including the 5′ UTR) and ligated them to a cDNA 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 cassette induced a high level of HSA in dense cultures grown on rich media. Thus, the GCN4-based expression system (pGES) provides high protein quantities. pGES is the first expression vector to be induced at the translational level.