Fusion of the Saccharomyces cerevisiae leu2 Gene to an Escherichia coli β-Galactosidase Gene

Abstract

The promoter and translation initiation region of the Saccharomyces cerevisiae leu2 gene was fused to the Escherichia coli β-galactosidase gene. This fusion located the control region of the leu gene and orientated its direction of expression. When the fusion was placed into yeast cells, β-galactosidase was expressed under the same regulatory pattern as the original leu2 gene product: its synthesis was repressed in the presence of leucine and threonine. Sensitive chromogenic substrates for β-galactosidase were used to detect expression in isolated colonies growing on agar medium. Mutant yeast cells with increased β-galactosidase activity were identified by the color of the colonies they formed. One class of mutants obtained appeared to affect ars1 plasmid maintenance, and another class appeared to affect β-galactoside uptake.