Positive Autoregulation of the Yeast Transcription Factor Pdr3p, Which is Involved in Control of Drug Resistance

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Abstract
Simultaneous resistance to an array of drugs with different cytotoxic activities is a property of Saccharomyces cerevisiae, in which the protein Pdr3p has recently been shown to play a role as a transcriptional regulator. We provide evidence that the yeast PDR3 gene, which encodes a zinc finger transcription factor implicated in certain drug resistance phenomena, is under positive autoregulation by Pdr3p. DNase I footprinting analyses using bacterially expressed Pdr3p showed specific recognition by this protein of at least two upstream activating sequences in the PDR3 promoter. The use of lacZ reporter constructs, a mutational analysis of the upstream activating sequences, as well as band shift experiments enabled the identification of two 5'TC CGCGGA3' sequence motifs in the PDR3 gene as consensus elements for the binding of Pdr3p. Several similar sequence motifs can be found in the promoter of PDR5, a gene encoding an ATP-dependent drug pump whose Pdr3p-induced overexpression is responsible for drug resistance phenomena. Recently one of these sequence elements was shown to be the target of Pdr3p to elevate the level of PDR5 transcription. Finally, we provide evidence in the absence of PDR1 for a PDR3-controlled transcriptional induction of the drug pump by cycloheximide and propose a model for the mechanism governing the transcriptional autoregulation of Pdr3p.