TRANSCRIPTIONAL CONTROL OF THE YEAST PDR5 GENE BY THE PDR3 GENE-PRODUCT

Saccharomyces cerevisiae cells possess the ability to simultaneously a cquire resistance to an array of drugs with different cytotoxic activi ties. The genes involved in this acquisition are referred to as pleiot ropic drug resistant (PDR) genes. Several semidominant, drug resistanc e-encoding PDR mutations have been found that map near the centromere on chromosome II, including PDR3-1 and PDR4-1. DNA sequencing of chrom osome II identified a potential open reading frame, designated YBL03-2 3, that has the potential to encode a protein with strong sequence sim ilarity to the product of the PDR1 gene, a zinc finger-containing tran scription factor. Here,ve show that YBL03-23 is allelic with PDR3. The presence of a functional copy of either PDR1 or PDR3 is essential for drug resistance and expression of a putative membrane transporter-enc oding gene, PDR5. Deletion mapping of the PDR5 promoter identified a r egion from -360 to -112 that is essential for expression of this gene. DNase I footprinting analysis using bacterially expressed Pdr3p showe d specific recognition by this protein of at least one site in the -36 0/-112 interval in the PDR5 promoter. A high-copy-number plasmid carry ing the PDR3 gene elevated resistance to both oligomycin and cyclohexi mide. Increasing the number of PDR3 gene copies in a Delta pdr5 strain increased oligomycin resistance but was not able to correct the cyclo heximide hypersensitivity that results from loss of PDR5. These data a re consistent with the notion that PDR3 acts to increase cycloheximide resistance by elevating the level of PDR5 transcription, while PDR3-m ediated oligomycin resistance acts through some other target gene.