Enhancing drug accumulation in Saccharomyces cerevisiae by repression of pleiotropic drug resistance genes with chimeric transcription repressors.

Yeast is a powerful model system for studying the action of small-molecule therapeutics. An important limitation has been low efficacy of many small molecules in yeast due to limited intracellular accumulation. We used the DNA binding domain of the pleiotropic drug resistance regulator pleiotropic drug resistance 1 (Pdr1) fused in-frame to transcription repressors to repress Pdr1-regulated genes. Expression of these chimeric regulators conferred dominant enhancement of sensitivity to a different class of compounds and led to greatly diminished levels of Pdr1p-regulated transcripts, including the yeast p-glycoprotein homolog Pdr5. Enhanced sensitivity was seen for a wide range of small molecules. Biochemical measurements demonstrated enhanced accumulation of rhodamine in yeast cells expressing the chimeric repressors. These repressors of Pdr1p-regulated transcripts can be introduced into large collections of strains such as the Saccharomyces cerevisiae deletion set and enhance the utility of yeast for studying drug action and for mechanism-based drug discovery.