Physiological and genetic modulation of inducible expression of Escherichia coli β-galactosidase in Saccharomyces cerevisiae

Saccharomyces cerevisiae cells transformed with plasmids bearing the lacZ gene from Escherichia coli, under the control of the inducible GAL1-10/CYC1 promoter, produce the highest amount of β-galactosidase during a transient physiological condition corresponding to the early stationary phase of growth. This enhanced enzyme expression is characteristic of active cycling cells down-modulated by the nutrients. By increasing the dosage of the GAL4 gene, after transformation of yeast cells with a multicopy plasmid bearing the GAL4 gene, a positive but limited enhancement of enzyme expression is induced