The PDR5 gene encodes the major multidrug resistance efflux pump in Saccharomyces cerevisiae. In drug‐resistant cells, the hyperactive Pdr1p or Pdr3p transcriptional activators are responsible for ...the PDR5 upregulation. In this work, it is shown that the RPD3 gene encoding the histone deacetylase that functions as a transcriptional corepressor at many promoters and the ROM2 gene coding for the GDP/GTP exchange protein for Rho1p and Rho2p participating in signal transduction pathways are required for PDR5 transcription under cycloheximide‐induced and noninduced conditions. Transposon insertion mutations in ROM2, RPD3 and some other genes encoding specific subunits of the large Rpd3L protein complex resulted in enhanced susceptibility of mutant cells to antifungals. In the rpd3Δ and rom2Δ mutants, the level of PDR5 mRNA and the rate of rhodamine 6G efflux were reduced. Unlike rpd3Δ, in rom2Δ mutant cells the drug hypersensitivity and the defect in PDR5 expression were suppressed by PDR1 or PDR3 overexpressed from heterologous promoters and by the hyperactive pdr3‐9 mutant allele. The results indicate that Rpd3p histone deacetylase participating in chromatin remodeling and Rom2p participating in the cell integrity pathway are involved in the control of PDR5 expression and modulation of multidrug resistance in yeast.
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