POSITIVE AUTOREGULATION OF THE YEAST TRANSCRIPTION FACTOR PDR3P, WHICH IS INVOLVED IN CONTROL OF DRUG-RESISTANCE

Simultaneous resistance to an array of drugs with different cytotoxic activities is a property of Saccharomyces cerevisiae, in which the pro tein Pdr3p has recently been shown to play a role as a transcriptional regulator. We provide evidence that the yeast PDR3 gene, which encode s a zinc finger transcription factor implicated in certain drug resist ance phenomena, is under positive autoregulation by Pdr3p. DNase I foo tprinting analyses using bacterially expressed Pdr3p showed specific r ecognition by this protein of at least two upstream activating sequenc es in the PDR3 promoter. The use of lacZ reporter constructs, a mutati onal analysis of the upstream activating sequences, as well as band sh ift experiments enabled the identification of two 5'TC CGCGGA3' sequen ce motifs in the PDR3 gene as consensus elements for the binding of Pd r3p. Several similar sequence motifs can be found in the promoter of P DRS, a gene encoding an ATP-dependent drug pump whose Pdr3p-induced ov erexpression is responsible for drug resistance phenomena. Recently on e of these sequence elements was shown to be the target of Pdr3p to el evate the level of PDRS transcription. Finally, we provide evidence in the absence of PDR1 for a PDR3-controlled transcriptional induction o f the drug pump by cycloheximide and propose a model for the mechanism governing the transcriptional autoregulation of Pdr3p.