Mutations in the yeast PDR3, PDR4, PDR7 and PDR9 pleiotropic (multiple) drug resistance loci affect the transcript level of an ATP binding cassette transporter encoding gene, PDR5.

The yeast pleiotropic (multiple drug) resistance gene PDR5 encodes a product with homology to a large number of membrane transport proteins including the mammalian multiple drug resistance family. In this study, we identified four genes on chromosome II that affect the steady-state level of PDR5 transcript in addition to a previously identified positive regulator, PDR1. The genes in question are PDR3, PDR4, PDR7 and PDR9. We also analyzed the interaction between PDR5 and YAP1. YAP1 encodes a positive regulator with a leucine zipper motif that causes pleiotropic drug resistance when overproduced. YAP1-mediated pleiotropic drug resistance is not dependent on the presence of PDR5 and must act through other genes.