The yeast zinc finger regulators Pdr1p and Pdr3p control pleiotropic drug resistance (PDR) as homo- and heterodimers in vivo

Expression regulation of the yeast PDR5 ATP-binding cassette (ABC) transporter suggests a role in cellular detoxification during the exponential growth phase

The yeast ATP-binding cassette transporter Pdr5p mediates pleiotropic drug resistance (PDR) by effluxing a variety of xenobiotics. Immunoblotting demonstrates that Pdr5p levels are high in the logarithmic growth phase, while its levels decrease sharply when cells exit exponential growth. Here, we show that PDR5 promoter activity is dramatically reduced when cells stop growing due to a limitation of glucose or nitrogen or when they approach stationary phase. Interestingly, Pdr3p, a major transcriptional regulator of PDR5, shows the same regulatory pattern. Feeding glucose to starved cells rapidly re-induces both PDR5 and PDR3 transcription. Importantly, diminished Pdr5p levels, as present after starvation, are rapidly restored in response to xenobiotic challenges that activate the transcription factors Pdr1p and Pdr3p. Our data indicate a role for yeast Pdr5p in cellular detoxification during exponential growth.

Competitive Promoter Occupancy by Two Yeast Paralogous Transcription Factors Controlling the Multidrug Resistance Phenomenon

Highly flexible gene expression programs are required to allow cell growth in the presence of a wide variety of chemicals. We used genome-wide expression analyses coupled with chromatin immunoprecipitation experiments to study the regulatory relationships between two very similar yeast transcription factors involved in the control of the multidrug resistance phenomenon. Yrm1 (Yor172w) is a new zinc finger transcription factor, the overproduction of which decreases the level of transcription of the target genes of Yrr1, a zinc finger transcription factor controlling the expression of several membrane transporter-encoding genes. Surprisingly, the absence of YRR1 releases the transcriptional activity of Yrm1, which then up-regulates 23 genes, 14 of which are also direct target genes of Yrr1. Chromatin immunoprecipitation experiments confirmed that Yrm1 binds to the promoters of the up-regulated genes only in yeast strains from which YRR1 has been deleted. This sophisticated regulatory program can be associated with drug resistance phenotypes of the cell. The program-specific distribution of paired transcription factors throughout the genome may be a general mechanism by which similar transcription factors regulate overlapping gene expression programs in response to chemical stress.

Aft1p and Aft2p mediate iron-responsive gene expression in yeast through related promoter elements

The transcription factors Aft1p and Aft2p from Saccharomyces cerevisiae regulate the expression of genes that are involved in iron homeostasis. In vitro studies have shown that both transcription factors bind to an iron-responsive element (FeRE) that is present in the upstream region of genes in the iron regulon. We have used DNA microarrays to distinguish the genes that are activated by Aft1p and Aft2p and to establish for the first time that each factor gives rise to a unique transcriptional profile due to the differential expression of individual iron-regulated genes. We also show that both Aft1p and Aft2p mediate the in vivo expression of FET3 and FIT3 through a consensus FeRE. In addition, both proteins regulate MRS4 via a variant FeRE with Aft2p being the stronger activator from this particular element. Like other paralogous pairs of transcription factors within S. cerevisiae, Aft1p and Aft2p are able to interact with the same promoter elements while maintaining specificity of gene activation.