Construction and Characterization of a Temperature‐Sensitive Expression System in Recombinant Yeast

A temperature‐regulated system for the expression of cloned genes has been developed and studied in recombinant yeast. A temperature‐sensitive (ts) strain of Saccharomyces cerevisiae was constructed which, in conjunction with plasmid promoters controlled by the yeast galactose regulatory circuit, allows induction of cloned gene product synthesis by temperature‐shift. Induction of cloned gene expression by temperature‐shift in the ts strain was compared with induction by galactose addition in a non‐ts, but otherwise identical, strain. In batch fermentations at 35°C, the levels of product protein produced by temperature‐shift induction were comparable or better than those produced by galactose induction. However, higher levels were formed by galactose induction at the preferred growth temperature of 30°C. At either temperature, β‐galactosidase synthesis was greatest when the ts strain was cultivated in galactose‐containing medium. Continuous culture experiments were performed to further characterize and compare the two induction methods. Induction by galactose addition at 30°C was superior, indicating the importance of temperature for cell growth and cloned gene expression.