Abstract
In Saccharomyces cerevisiae, the Rpd3L complex contains a histone deacetylase, Rpd3, and the DNA binding proteins, Ume6 and Ash1, and acts as a transcriptional repressor or activator. We previously showed that RPD3 and UME6 are required for the activation of PDR5, which encodes a major efflux pump, and pleiotropic drug resistance (PDR) in ρ0/− cells, which lack mitochondrial DNA. However, there are inconsistent reports regarding whether RPD3 and UME6 are required for Pdr5-mediated PDR in ρ+ cells with mitochondrial DNA. Since PDR5 expression or PDR in the ρ+ cells of the rpd3Δ and ume6Δ mutants have primarily been examined using fermentable media, mixed cultures of ρ+ and ρ0/− cells could be used. Therefore, we examined whether RPD3 and UME6 are required for basal and drug-induced PDR5 transcription and PDR in ρ+ cells using fermentable and nonfermentable media. UME6 suppresses the basal transcription levels of the ABC transporters, including PDR5, and drug resistance in ρ+ cells independent of the carbon source used in the growth medium. In contrast, RPD3 is required for drug resistance but did not interfere with the basal PDR5 mRNA levels. UME6 is also required for the cycloheximide-induced transcription of PDR5 in nonfermentable media but not in fermentable media.
Highlights
In the yeast Saccharomyces cerevisiae, ATP-binding cassette (ABC) transporters, such asPdr5, Snq2, and Yor1, efflux a variety of functionally and structurally unrelated compounds, such as fluconazole and cycloheximide from cells [1–5]
To examine whether RPD3 and UME6 are responsible for pleiotropic drug resistance (PDR) in ρ+ cells of S. cerevisiae, a spot dilution assay using yeast extract peptone glycerol (YPG) medium containing the nonfermentable carbon source glycerol was carried out to determine the resistance or susceptibility in the ρ+ cells of the rpd3∆ and ume6∆ mutants to the PDR substrates fluconazole and cycloheximide. ρ+ cells of the wild-type strain required a lower concentration of fluconazole and cycloheximide for growth inhibition in YPG medium than in yeast extract peptone dextrose (YPD) medium, which is consistent with previous reports [45]
We have shown that UME6 suppresses the basal transcription levels of the ABC transporters, including PDR5, and drug resistance in the ρ+ cells of S. cerevisiae independent of the carbon source used in the growth medium while RPD3 does not interfere with basal PDR5 transcription but contributes to drug resistance
Summary
In the yeast Saccharomyces cerevisiae, ATP-binding cassette (ABC) transporters, such as. Snq, and Yor, efflux a variety of functionally and structurally unrelated compounds, such as fluconazole and cycloheximide from cells [1–5]. The overexpression of the ABC transporters causes multidrug resistance, which is referred to as pleiotropic drug resistance (PDR) in S. cerevisiae [6,7]. The ABC transporters PDR5, SNQ2, YOR1, PDR10, and PDR15 are regulated by the paralogous Zn2 Cys transcription factors, Pdr and/or Pdr3 [1,8,9]. Pdr or Pdr recognizes the pleiotropic drug response elements (PDRE) DNA consensus motifs in the promoter regions of PDR5, SNQ2, YOR1, PDR10, and PDR15 [9–12]. PDR3 has two PDREs in its promoter region that are recognized by Pdr and Pdr1 [13]. PDR3 is subject to positive transcriptional autoregulation by Pdr and transcriptional regulation by Pdr, via these two PDREs [13]. The basal expression levels of PDR5 and SNQ2 and PDR are reduced by PDR1 deletion in ρ+ cells, which contains mitochondrial
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