Diazaborine resistance in the yeast Saccharomyces cerevisiae reveals a link between YAP1 and the pleiotropic drug resistance genes PDR1 and PDR3.

We have investigated the mechanisms underlying resistance to the drug diazaborine in Saccharomyces cerevisiae. We used UV mutagenesis to generate resistant mutants, which were divided into three different complementation groups. The resistant phenotype in these groups was found to be caused by allelic forms of the genes AFG2, PDR1, and PDR3. The AFG2 gene encodes an AAA (ATPases associated to a variety of cellular activities) protein of unknown function, while PDR1 and PDR3 encode two transcriptional regulatory proteins involved in pleiotropic drug resistance development. The isolated PDR1-12 and PDR3-33 alleles carry mutations that lead to a L1044Q and a Y276H exchange, respectively. In addition, we report that overexpression of Yap1p, the yeast homologue of the transcription factor AP1, results in a diazaborine-resistant phenotype. The YAP1-mediated diazaborine resistance is dependent on the presence of functional PDR1 and PDR3 genes, although PDR3 had a more pronounced effect. These results provide the first evidence for a functional link between the Yap1p-dependent stress response pathway and Pdr1p/Pdr3p-dependent development of pleiotropic drug resistance.