Expression regulation of the yeast PDR5 ATP-binding cassette (ABC) transporter suggests a role in cellular detoxification during the exponential growth phase

The yeast ATP-binding cassette transporter Pdr5p mediates pleiotropic drug resistance (PDR) by effluxing a variety of xenobiotics. Immunoblotting demonstrates that Pdr5p levels are high in the logarithmic growth phase, while its levels decrease sharply when cells exit exponential growth. Here, we show that PDR5 promoter activity is dramatically reduced when cells stop growing due to a limitation of glucose or nitrogen or when they approach stationary phase. Interestingly, Pdr3p, a major transcriptional regulator of PDR5, shows the same regulatory pattern. Feeding glucose to starved cells rapidly re-induces both PDR5 and PDR3 transcription. Importantly, diminished Pdr5p levels, as present after starvation, are rapidly restored in response to xenobiotic challenges that activate the transcription factors Pdr1p and Pdr3p. Our data indicate a role for yeast Pdr5p in cellular detoxification during exponential growth.