Construction and characterization of bidirectional expression vectors in Saccharomyces cerevisiae

The GAL1 and GAL10 genes of Saccharomyces cerevisiae are transcribed divergently and transcription of both genes can be induced by galactose and repressed by glucose. This study describes the construction and characterization of 8 bidirectional expression vectors. These vectors carry both a modified inducible GAL promoter in one direction and a constitutive GPD promoter in the reverse direction. When the gene-encoded alpha-galactosidase was cloned into the modified GAL1 and GAL10 vectors, promoter activity was 85% of wild-type for the GAL1 promoter and 90% of wild-type for the GAL10 promoter, respectively. The modified GAL promoters and GPD promoter did not interfere with one another in the bidirectional vectors. Furthermore, yeast overexpressing human Bax under the control of either modified GAL1 or modified GAL10 in a bidirectional vector conferred a lethal phenotype that was rescued by coexpression of human Bcl-2 under the control of the GPD promoter in the same vector. These eight vectors can be used to express lethal genes and screen for genes that rescue the yeast from the lethal gene product.