Transcriptional activation of FLR1 gene during Saccharomyces cerevisiae adaptation to growth with benomyl: role of Yap1p and Pdr3p

Unraveling the secrets: Evolution of resistance mediated by membrane proteins

Membrane protein-mediated resistance is a multidisciplinary challenge that spans fields such as medicine, agriculture, and environmental science. Understanding its complexity and devising innovative strategies are crucial for treating diseases like cancer and managing resistant pests in agriculture. This paper explores the dual nature of resistance mechanisms across different organisms: On one hand, animals, bacteria, fungi, plants, and insects exhibit convergent evolution, leading to the development of similar resistance mechanisms. On the other hand, influenced by diverse environmental pressures and structural differences among organisms, they also demonstrate divergent resistance characteristics. Membrane protein-mediated resistance mechanisms are prevalent across animals, bacteria, fungi, plants, and insects, reflecting their shared survival strategies evolved through convergent evolution to address similar survival challenges. However, variations in ecological environments and biological characteristics result in differing responses to resistance. Therefore, examining these differences not only enhances our understanding of adaptive resistance mechanisms but also provides crucial theoretical support and insights for addressing drug resistance and advancing pharmaceutical development.

Activity of the pleiotropic drug resistance transcription factors Pdr1p and Pdr3p is modulated by binding site flanking sequences

The transcription factors Pdr1p and Pdr3p regulate pleiotropic drug resistance (PDR) in Saccharomyces cerevisiae via the PDR responsive elements (PDREs) to modulate gene expression. However, the exact mechanisms underlying the differences in their regulons remain unclear. Employing genomic occupancy profiling (CUT&RUN), binding assays, and transcription studies, we characterized the differences in sequence specificity between transcription factors. Findings reveal distinct preferences for core PDRE sequences and the flanking sequences for both proteins. While flanking sequences moderately alter DNA binding affinity, they significantly impact Pdr1/3p transcriptional activity. Notably, both proteins demonstrated the ability to bind half sites, showing potential enhancement of transcription from adjacent PDREs. This insight sheds light on ways Pdr1/3p can differentially regulate PDR.

Unraveling the Half and Full Site Sequence Specificity of the Saccharomyces cerevisiae Pdr1p and Pdr3p Transcription Factors

The transcription factors Pdr1p and Pdr3p regulate pleotropic drug resistance (PDR) in Saccharomyces cerevisiae , via the PDR responsive elements (PDREs) to modulate gene expression. However, the exact mechanisms underlying the differences in their regulons remain unclear. Employing genomic occupancy profiling (CUT&RUN), binding assays, and transcription studies, we characterized the differences in sequence specificity between transcription factors. Findings reveal distinct preferences for core PDRE sequences and the flanking sequences for both proteins. While flanking sequences moderately alter DNA binding affinity, they significantly impact Pdr1/3p transcriptional activity. Notably, both proteins demonstrated the ability to bind half sites, showing potential enhancement of transcription from adjacent PDREs. This insight sheds light on ways Pdr1/3 can differentially regulate PDR.

Influence of tetraconazole on the proteome profile of Saccharomyces cerevisiae Lalvin T73™ strain

This work aimed to evaluate the modifications on the proteome profile of Saccharomyces cerevisiae T73™ strain as a consequence of its adaptive response to the presence of tetraconazole molecules in the fermentation medium. Pasteurised grape juices were separately supplemented with tetraconazole or a commercial formulation containing 12.5% w/v of tetraconazole at two concentration levels. In addition, experiments without fungicides were developed for comparative purposes. Proteome profiles of yeasts cultured in the presence or absence of fungicide molecules were different. Independently of the fungicide treatment applied, the highest variations concerning the control sample were observed for those proteins involved in metabolic processes, especially in the metabolism of nitrogen compounds. Tetraconazole molecules altered the abundance of several enzymes involved in the biosynthesis of amino acids, purines, and ergosterol. Moreover, differences in the abundance of several enzymes of the TCA cycle were found. Changes observed were different between the active substance and the commercial formulation. SIGNIFICANCE: The presence of fungicide residues in grape juice has direct implications on the development of the aromatic profile of the wine. These alterations could be related to changes in the secondary metabolism of yeasts. However, the molecular mechanisms involved in the response of yeasts to fungicide residues remains quite unexplored. Through this exhaustive proteomic study, alterations in the amino acids biosynthesis pathways due to the presence of the tetraconazole molecules were observed. Amino acids are precursors of some important higher alcohols and ethyl acetates (such as methionol, 2-phenylethanol, isoamyl alcohol or 2-phenylacetate). Besides, the effect of tetraconazole on the ergosterol biosynthesis pathway could be related to a higher production of medium-chain fatty acids and their corresponding ethyl acetates.

The MFS-type efflux pump Flr1 induced by Yap1 promotes canthin-6-one resistance in yeast

Screening for suppressors of canthin-6-one toxicity in yeast identified Yap1, a transcription factor involved in cell response to a broad range of injuries. Although canthin-6-one did not promote a significant oxidative stress, overexpression of YAP1 gene clearly increased resistance to this drug. We demonstrated that Yap1-mediated resistance involves the plasma membrane major-facilitator-superfamily efflux pump Flr1 but not the vacuolar ATP-binding-cassette transporter Ycf1. FLR1 overexpression was sufficient to reduce sensitivity to the drug, but strictly dependent on a functional YAP1 gene.

Qualitative modelling and formal verification of the FLR1 gene mancozeb response in Saccharomyces cerevisiae

BACKGROUND

Qualitative models allow understanding the relation between the structure and the dynamics of gene regulatory networks. The dynamical properties of these models can be automatically analysed by means of formal verification methods, like model checking. This facilitates the model-validation process and the test of new hypotheses to reconcile model predictions with the experimental data.

RESULTS

The authors report in this study the qualitative modelling and simulation of the transcriptional regulatory network controlling the response of the model eukaryote Saccharomyces cerevisiae to the agricultural fungicide mancozeb. The model allowed the analysis of the regulation level and activity of the components of the gene mancozeb-induced network controlling the transcriptional activation of the FLR1 gene, which is proposed to confer multidrug resistance through its putative role as a drug eflux pump. Formal verification analysis of the network allowed us to confront model predictions with the experimental data and to assess the model robustness to parameter ordering and gene deletion.

CONCLUSIONS

This analysis enabled us to better understand the mechanisms regulating the FLR1 gene mancozeb response and confirmed the need of a new transcription factor for the full transcriptional activation of YAP1. The result is a computable model of the FLR1 gene response to mancozeb, permitting a quick and cost-effective test of hypotheses prior to experimental validation.

Facilitated assembly of the preinitiation complex by separated tail and head/middle modules of the mediator

Mediator is a general coactivator of RNA polymerase II (RNA pol II) bridging enhancer-bound transcriptional factors with RNA pol II. Mediator is organized in three distinct subcomplexes: head, middle, and tail modules. The head and middle modules interact with RNA pol II, and the tail module interacts with transcriptional activators. Deletion of one of the tail subunits SIN4 results in derepression of a subset of genes, including FLR1, by a largely unknown mechanism. Here we show that derepression of FLR1 transcription in sin4Δ cells occurs by enhanced recruitment of the mediator as well as Swi/Snf and SAGA complexes. The tail and head/middle modules of the mediator behave as separate complexes at the induced FLR1 promoter. While the tail module remains anchored to the promoter, the head/middle modules are also found in the coding region. The separation of the tail and head/middle modules in sin4Δ cells is also supported by the altered stoichiometry of the tail and head/middle modules at several tested promoters. Deletion of another subunit of the tail module MED2 in sin4Δ cells results in significantly decreased transcription of FLR1, pointing to the importance of the integrity of the separated tail module in derepression. All tested genes exhibited increased recruitment of the tail domain; however, only genes with increased occupancy of the head/middle modules also displayed increased transcription. The separated tail module thus represents a promiscuous transcriptional factor that binds to many different promoters and is necessary for derepression of FLR1 in sin4Δ cells.

Yeast response and tolerance to polyamine toxicity involving the drug : H+ antiporter Qdr3 and the transcription factors Yap1 and Gcn4

The yeast QDR3 gene encodes a plasma membrane drug : H(+) antiporter of the DHA1 family that was described as conferring resistance against the drugs quinidine, cisplatin and bleomycin and the herbicide barban, similar to its close homologue QDR2. In this work, a new physiological role for Qdr3 in polyamine homeostasis is proposed. QDR3 is shown to confer resistance to the polyamines spermine and spermidine, but, unlike Qdr2, also a determinant of resistance to polyamines, Qdr3 has no apparent role in K(+) homeostasis. QDR3 transcription is upregulated in yeast cells exposed to spermine or spermidine dependent on the transcription factors Gcn4, which controls amino acid homeostasis, and Yap1, the main regulator of oxidative stress response. Yap1 was found to be a major determinant of polyamine stress resistance in yeast and is accumulated in the nucleus of yeast cells exposed to spermidine-induced stress. QDR3 transcript levels were also found to increase under nitrogen or amino acid limitation; this regulation is also dependent on Gcn4. Consistent with the concept that Qdr3 plays a role in polyamine homeostasis, QDR3 expression was found to decrease the intracellular accumulation of [(3)H]spermidine, playing a role in the maintenance of the plasma membrane potential in spermidine-stressed cells.

Insights into the mechanisms of toxicity and tolerance to the agricultural fungicide mancozeb in yeast, as suggested by a chemogenomic approach

Abstract Saccharomyces cerevisiae was used to uncover the mechanisms underlying tolerance and toxicity of the agricultural fungicide mancozeb, linked to cancer and Parkinson's disease development. Chemogenomics screening of a yeast deletion mutant collection revealed 286 genes that provide protection against mancozeb toxicity. The most significant Gene Ontology (GO) terms enriched in this dataset are associated to transcriptional machinery, vacuolar organization and biogenesis, intracellular trafficking, and cellular pH regulation. Clustering based on physical and genetic interactions further highlighted the role of oxidative stress response, protein degradation and carbohydrate/energy metabolism in mancozeb stress tolerance. Mancozeb was found to act in yeast as a thiol-reactive compound, but not as a free radical or reative oxygen species (ROS) inducer, leading to massive oxidation of protein cysteins, consistent with the requirement of genes involved in glutathione biosynthesis and reduction and in protein degradation to provide mancozeb resistance. The identification of Botrytis cinerea homologues of yeast mancozeb tolerance determinants is expected to guide studies on mancozeb mechanisms of action and tolerance in phytopathogenic fungi. The generated networks of protein-protein associations of yeast mancozeb tolerance determinants and their human orthologues share a high degree of similarity. This toxicogenomics analysis may, thus, increase the understanding of mancozeb toxicity and adaptation mechanisms in humans.

Overexpression of SNG1 causes 6-azauracil resistance in Saccharomyces cerevisiae

The mechanism of action of 6AU, a growth inhibitor for many microorganisms causing depletion of intracellular nucleotide pools of GTP and UTP, is not well understood. To gain insight into the mechanisms leading to 6AU resistance, and in an attempt to uncover novel genes required for this resistance, we undertook a high-copy-number suppressor screening to identify genes whose overexpression could repair the 6AU(S) growth defect caused by rpb1 mutations in Saccharomyces cerevisiae. We have identified SNG1 as a multicopy suppressor of the 6AU(S) growth defect caused by the S. cerevisiae rpb1 mutant. The mechanism by which Sng1 causes 6AU resistance is independent of the transcriptional elongation and of the nucleotide-pool regulation through Imd2 and Ura2, as well as of the Ssm1-mediated 6AU detoxification. This resistance to 6AU is not extended to other uracil analogues, such as 5-fluorouracil, 5FU. In addition, our results suggest that 6AU enters S. cerevisiae cells through the uracil permease Fur4. Our results demonstrate that Sng1 is localised in the plasma membrane and evidence SNG1 and FUR4 genes as determinants of resistance and susceptibility to this inhibitory compound, respectively. Taken together, these results show new mechanisms involved in the resistance and susceptibility to 6AU.

Drug:H+ antiporters in chemical stress response in yeast

The emergence of widespread multidrug resistance (MDR) is a serious challenge for therapeutics, food-preservation and crop protection. Frequently, MDR is a result of the action of drug-efflux pumps, which are able to catalyze the extrusion of unrelated chemical compounds. This review summarizes the current knowledge on the Saccharomyces cerevisiae drug:H+ antiporters of the major facilitator superfamily (MFS), a group of MDR transporters that is still characterized poorly in eukaryotes. Particular focus is given here to the physiological role and expression regulation of these transporters, while we provide a unified view of new data emerging from functional genomics approaches. Although traditionally described as drug pumps, evidence reviewed here corroborates the hypothesis that several MFS-MDR transporters might have a natural substrate and that drug transport might occur only fortuitously or opportunistically. Their role in MDR might even result from the transport of endogenous metabolites that affect the partition of cytotoxic compounds indirectly. Finally, the extrapolation of the gathered knowledge on the MDR phenomenon in yeast to pathogenic fungi and higher eukaryotes is discussed.

Adaptive response to the antimalarial drug artesunate in yeast involves Pdr1p/Pdr3p-mediated transcriptional activation of the resistance determinants TPO1 and PDR5

The expression of the transcription regulator Pdr1p and its target genes PDR5 and TPO1 is required for Saccharomyces cerevisiae adaptation and resistance to artesunate, a promising antimalarial drug, also active against tumour cells and viruses. PDR5 and TPO1 encode plasma membrane multidrug transporters of the ATP-binding cassette and the major facilitator superfamilies, respectively. The transcriptional activation of TPO1 (10-fold) and PDR5 (13-fold) was registered after 30 min of exposure of the unadapted yeast population to acute artesunate-induced stress, being significantly reduced in the absence of Pdr1p and abolished in the absence of Pdr1p and Pdr3p. Maximum TPO1 mRNA levels were rapidly reduced to basal values following adaptation of the yeast population to artesunate, while high PDR5 levels were maintained during drug-stressed exponential growth.

Identification of promoter elements responsible for the regulation of MDR1 from Candida albicans, a major facilitator transporter involved in azole resistance

Upregulation of the MDR1 (multidrug resistance 1) gene is involved in the development of resistance to antifungal agents in clinical isolates of the pathogen Candida albicans. To better understand the molecular mechanisms underlying the phenomenon, the cis-acting regulatory elements present in the MDR1 promoter were characterized using a beta-galactosidase reporter system. In an azole-susceptible strain, transcription of this reporter is transiently upregulated in response to either benomyl or H(2)O(2), whereas its expression is constitutively high in an azole-resistant strain (FR2). Two cis-acting regulatory elements within the MDR1 promoter were identified that are necessary and sufficient to confer the same transcriptional responses on a heterologous promoter (CDR2). One, a benomyl response element (BRE), is situated at position -296 to -260 with respect to the ATG start codon. It is required for benomyl-dependent MDR1 upregulation and is also necessary for constitutive high expression of MDR1. A second element, termed H(2)O(2) response element (HRE), is situated at position -561 to -520. The HRE is required for H(2)O(2)-dependent MDR1 upregulation, but dispensable for constitutive high expression. Two potential binding sites (TTAG/CTAA) for the bZip transcription factor Cap1p (Candida AP-1 protein) lie within the HRE. Moreover, inactivation of CAP1 abolished the transient response to H(2)O(2). Cap1p, which has been previously implicated in cellular responses to oxidative stress, may thus play a trans-acting and positive regulatory role in the H(2)O(2)-dependent transcription of MDR1. A minimal BRE (-290 to -273) that is sufficient to detect in vitro sequence-specific binding of protein complexes in crude extracts prepared from C. albicans was also defined. Interestingly, the sequence includes a perfect match to the consensus binding sequence of Mcm1p, raising the possibility that MDR1 may be a direct target of this MADS box transcriptional activator. In conclusion, while the identity of the trans-acting factors that bind to the BRE and HRE remains to be confirmed, the tools developed during this characterization of the cis-acting elements of the MDR1 promoter should now serve to elucidate the nature of the components that modulate its activity.

The bZip transcription factor Cgap1p is involved in multidrug resistance and required for activation of multidrug transporter gene CgFLR1 in Candida glabrata

Transcriptional regulation in response to environmental challenges is crucial for survival of many organisms. In this study, we characterized structural and functional properties of CgAP1, a Saccharomyces cerevisiae YAP1 ortholog, which encodes a transcription factor involved in various stress responses. Deletion of CgAP1 led to decreased resistance to hydrogen peroxide, 4-nitroquinoline-N-oxide (4-NQO), benomyl, and cadmium chloride, which could be fully recovered by reintroduction of an intact CgAP1. CgAP1 was shown to function in S. cerevisiae as it restored the drug resistance of the yap1 mutant. Moreover, overexpression of CgAP1 in a S. cerevisiae wild-type strain increased its resistance to cycloheximide, 1,10-phenanthroline, 4-NQO, and fluconazole. Overexpression of CgAP1 also phenotypically suppressed the drug sensitivity of two Yap1p-regulated transporter mutants, Deltaatr1 and Deltaflr1, to diamide, 4-NQO, and cadmium. Northern blot analysis indicated that Cgap1p regulates the benomyl-induced expression of CgFLR1, a homolog of S. cerevisiae FLR1, which encodes a transporter of the major facilitator superfamily. In contrast to the S. cerevisiae flr1 mutant, deletion of CgFLR1 in C. glabrata only resulted in increased sensitivity to benomyl, diamide, and menadione, but not 4-NQO, cycloheximide, or fluconazole. Taken together, this report demonstrated that CgAP1 plays a critical role in response to various stresses in C. glabrata and reduces the stress through transcriptional activation of its target genes including CgFLR1.

A stress regulatory network for co‐ordinated activation of proteasome expression mediated by yeast heat shock transcription factor

Heat shock transcription factor (HSF) mediates the transcriptional response of eukaryotic cells to heat, infection and inflammation, pharmacological agents, and other stresses. Although genes encoding heat shock proteins (HSPs) are the best characterized targets of HSF, recent genome-wide localization of Saccharomyces cerevisiae HSF revealed novel HSF targets involved in a wide range of cellular functions. One such target, the RPN4 gene, encodes a transcription factor that directly activates expression of a number of genes encoding proteasome subunits. Here we demonstrate that HSF co-ordinates a feed-forward gene regulatory circuit for RPN4 activation. We show that HSF activates expression of PDR3, encoding a multidrug resistance (MDR) transcription factor that also directly activates RPN4 gene expression. We demonstrate that the HSF binding site (HSE) in the RPN4 promoter is primarily responsible for heat- or methyl methanesulphonate induction of RPN4, with a minor contribution of Pdr3 binding sites (PDREs), while a Yap1 binding site (YRE) is responsible for RPN4 induction in response to oxidative stress. Furthermore, heat-induced expression of Rpn4 protein leads to expression of Rpn4 targets at later stages of heat stress, providing a temporal controlling mechanism for proteasome synthesis upon stress conditions that could result in irreversibly damaged proteins. In addition, the overlapping transcriptional regulatory networks involving HSF, Yap1 and Pdr3 suggest a close linkage between stress responses and pleiotropic drug resistance.

The YEASTRACT database: a tool for the analysis of transcription regulatory associations in Saccharomyces cerevisiae

We present the YEAst Search for Transcriptional Regulators And Consensus Tracking (YEASTRACT; ) database, a tool for the analysis of transcription regulatory associations in Saccharomyces cerevisiae. This database is a repository of 12 346 regulatory associations between transcription factors and target genes, based on experimental evidence which was spread throughout 861 bibliographic references. It also includes 257 specific DNA-binding sites for more than a hundred characterized transcription factors. Further information about each yeast gene included in the database was obtained from Saccharomyces Genome Database (SGD), Regulatory Sequences Analysis Tools and Gene Ontology (GO) Consortium. Computational tools are also provided to facilitate the exploitation of the gathered data when solving a number of biological questions as exemplified in the Tutorial also available on the system. YEASTRACT allows the identification of documented or potential transcription regulators of a given gene and of documented or potential regulons for each transcription factor. It also renders possible the comparison between DNA motifs, such as those found to be over-represented in the promoter regions of co-regulated genes, and the transcription factor-binding sites described in the literature. The system also provides an useful mechanism for grouping a list of genes (for instance a set of genes with similar expression profiles as revealed by microarray analysis) based on their regulatory associations with known transcription factors.

Expression of FLR1 transporter requires phospholipase C and is repressed by Mediator

In budding yeast, phosphoinositide-specific phospholipase C (Plc1p encoded by PLC1 gene) is important for function of kinetochores. Deletion of PLC1 results in benomyl sensitivity, alterations in chromatin structure of centromeres, mitotic delay, and a higher frequency of chromosome loss. Here we intended to utilize benomyl sensitivity as a phenotype that would allow us to identify genes that are important for kinetochore function and are downstream of Plc1p. However, our screen identified SIN4, encoding a component of the Mediator complex of RNA polymerase II. Deletion of SIN4 gene (sin4Delta) does not suppress benomyl sensitivity of plc1Delta cells by improving the function of kinetochores. Instead, benomyl sensitivity of plc1Delta cells is caused by a defect in expression of FLR1, and the suppression of benomyl sensitivity in plc1Delta sin4Delta cells occurs by derepression of FLR1 transcription. FLR1 encodes a plasma membrane transporter that mediates resistance to benomyl. Several other mutations in the Mediator complex also result in significant derepression of FLR1 and greatly increased resistance to benomyl. Thus, benomyl sensitivity is not a phenotype exclusively associated with mitotic spindle defect. These results demonstrate that in addition to promoter-specific transcription factors that are components of the pleiotropic drug resistance network, expression of the membrane transporters can be regulated by Plc1p, a component of a signal transduction pathway, and by Mediator, a general transcription factor. The results thus suggest another layer of complexity in regulation of pleiotropic drug resistance.

Activation of an AP1-like transcription factor of the maize pathogen Cochliobolus heterostrophus in response to oxidative stress and plant signals

Redox sensing is a ubiquitous mechanism regulating cellular activity. Fungal pathogens face reactive oxygen species produced by the host plant's oxidative burst in addition to endogenous reactive oxygen species produced during aerobic metabolism. An array of preformed and induced detoxifying enzymes, including superoxide dismutase, catalases, and peroxidases, could allow fungi to infect plants despite the oxidative burst. We isolated a gene (CHAP1) encoding a redox-regulated transcription factor in Cochliobolus heterostrophus, a fungal pathogen of maize. CHAP1 is a bZIP protein that possesses two cysteine-rich domains structurally and functionally related to Saccharomyces cerevisiae YAP1. Deletion of CHAP1 in C. heterostrophus resulted in decreased resistance to oxidative stress caused by hydrogen peroxide and menadione, but the virulence of chap1 mutants was unaffected. Upon activation by oxidizing agents or plant signals, a green fluorescent protein (GFP)-CHAP1 fusion protein became localized in the nucleus. Expression of genes encoding antioxidant proteins was induced in the wild type but not in chap1 mutants. Activation of CHAP1 occurred from the earliest stage of plant infection, in conidial germ tubes on the leaf surface, and persisted during infection. Late in the course of infection, after extensive necrotic lesions were formed, GFP-CHAP1 redistributed to the cytosol in hyphae growing on the leaf surface. Localization of CHAP1 to the nucleus may, through changes in the redox state of the cell, provide a mechanism linking extracellular cues to transcriptional regulation during the plant-pathogen interaction.

Drug-induced regulation of the MDR1 promoter in Candida albicans

Resistance of Candida albicans to azole antifungal drugs is mediated by two types of efflux pumps, encoded by the MDR1 gene and the CDR gene family. MDR1 mRNA levels in a susceptible clinical isolate are induced by benomyl (BEN) but not by other drugs previously shown to induce MDR1. To monitor MDR1 expression under several conditions, the MDR1 promoter was fused to the Renilla reniformis luciferase reporter gene (RLUC). The promoter was monitored for its responses to four oxidizing agents, five toxic hydrophobic compounds, and an alkylating agent, all shown to induce major facilitator pumps in other organisms. Deletion constructs of the MDR1 promoter were used to analyze the basal transcription of the promoter and its responses to the toxic compound BEN and the oxidizing agent tert-butyl hydrogen peroxide (T-BHP). The cis-acting elements in the MDR1 promoter responsible for induction by BEN were localized between -399 and -299 upstream of the start codon. The cis-acting elements responsible for MDR1 induction by T-BHP were localized between -601 and -500 upstream of the start codon. The T-BHP induction region contains a sequence that resembles the YAP1-responsive element (YRE) in Saccharomyces cerevisiae. This Candida YRE was placed upstream of a noninducible promoter in the luciferase construct, resulting in an inducible promoter. Inversion or mutation of the 7-bp YRE eliminated induction. Many of the drugs used in this analysis induce the MDR1 promoter at concentrations that inhibit cell growth. These analyses define cis-acting elements responsible for drug induction of the MDR1 promoter.

Saccharomyces cerevisiae Aqr1 is an internal-membrane transporter involved in excretion of amino acids

Excretion of amino acids by yeast cells was reported long ago but has not been characterized in molecular terms. It is typically favored by overproduction of the amino acid and/or impairment of its uptake. Here we describe the construction of a yeast strain excreting threonine and homoserine. Using this excretor strain, we then applied a reverse-genetics approach and found that the transporter encoded by the YNL065w/AQR1 gene, a protein thought to mediate H(+) antiport, is involved in homoserine and threonine excretion. Furthermore, overexpression of AQR1 led to increased excretion of several amino acids (alanine, aspartate, and glutamate) known to be relatively abundant in the cytosol. Transcription of the AQR1 gene is induced severalfold by a number of amino acids and appears to be under the negative control of Gcn4. An Aqr1-green fluorescent protein fusion protein is located in multiple internal membrane structures and appears to cycle continuously between these compartments and the plasma membrane. The Aqr1 sequence is significantly similar to the vesicular amine transporters of secretory vesicles of neuronal cells. We propose that Aqr1 catalyzes transport of excess amino acids into vesicles, which then release them in the extracellular space by exocytosis.

Early expression of yeast genes affected by chemical stress

The variety of environmental stresses is probably the major challenge imposed on transcription activators and the transcriptional machinery. To precisely describe the very early genomic response developed by yeast to accommodate a chemical stress, we performed time course analyses of the modifications of the yeast gene expression program which immediately follows the addition of the antimitotic drug benomyl. Similar analyses were conducted with different isogenic yeast strains in which genes coding for relevant transcription factors were deleted and coupled with efficient bioinformatics tools. Yap1 and Pdr1, two well-known key mediators of stress tolerance, appeared to be responsible for the very rapid establishment of a transient transcriptional response encompassing 119 genes. Yap1, which plays a predominant role in this response, binds, in vivo, promoters of genes which are not automatically up-regulated. We proposed that Yap1 nuclear localization and DNA binding are necessary but not sufficient to elicit the specificity of the chemical stress response.

Acetaminophen toxicity and resistance in the yeast Saccharomyces cerevisiae

Acetaminophen (paracetamol), one of the most widely used analgesics, is toxic under conditions of overdose or in certain disease conditions, but the mechanism of acetaminophen toxicity is still not entirely understood. To obtain fresh insights into acetaminophen toxicity, this phenomenon was investigated in yeast. Acetaminophen was found to be toxic to yeast cells, with erg mutants displaying hypersensitivity. Yeast cells grown in the presence of acetaminophen were found to accumulate intracellular acetaminophen, but no metabolic products of acetaminophen could be detected in these extracts. The toxicity response did not lead to an oxidative stress response, although it did involve Yap1p. The cytochrome P450 enzymes of yeast, Erg5p and Erg11p, did not appear to participate in this process, unlike the mammalian systems. Furthermore, we could not establish a central role for glutathione depletion or the cellular glutathione redox status in acetaminophen toxicity, suggesting differences from mammalian systems in the pathways causing toxicity. Investigations of the resistance mechanisms revealed that deletion of the glutathione-conjugate pumps Ycf1p (a target of Yap1p) and Bpt1p, surprisingly, led to acetaminophen resistance, while overexpression of the multidrug resistance pumps Snq2p and Flr1p (also targets of Yap1p) led to acetaminophen resistance. The Yap1p-dependent resistance to acetaminophen required a functional Pdr1p or Pdr3p protein, but not a functional Yrr1p. In contrast, resistance mediated by Pdr1p/Pdr3p did not require a functional Yap1p, and revealed a distinct hierarchy in the resistance to acetaminophen.

Saccharomyces cerevisiae multidrug transporter Qdr2p (Yil121wp): localization and function as a quinidine resistance determinant

This work reports the functional analysis of Saccharomyces cerevisiae open reading frame YIL121w, encoding a member of a family of drug:H(+) antiporters with 12 predicted membrane-spanning segments (DHA12 family). Like its close homologue Qdr1p, Yil121wp was localized at the plasma membrane, and its increased expression also led to increased tolerance to the antiarrhythmia and antimalarial drug quinidine. The quinidine resistance phenotype was confirmed for different yeast strains and growth media, including a prototrophic strain, and YIL121w was named the QDR2 gene. Both QDR1 and QDR2 were also implicated in yeast resistance to the herbicide barban (4-chloro-2-butynyl [3-chlorophenyl] carbamate), and the genes are functionally interchangeable with respect to both resistance phenotypes. The average intracellular pH of a yeast population challenged with quinidine added to the acidic growth medium was significantly below the intracellular pH of the unstressed population, suggesting plasma membrane permeabilization by quinidine with consequent increase of the H(+) influx rate. For the same extracellular quinidine concentration, internal acidification was more intense for the Deltaqdr2 deletant compared with the parental strain. Although QDR2 transcription was not enhanced in response to quinidine, the results confirmed that Qdr2p is involved in the active export of quinidine out of the cell, thus conferring resistance to the drug.

A general strategy to uncover transcription factor properties identifies a new regulator of drug resistance in yeast

We demonstrate a genomewide approach to determine the physiological role of a putative transcription factor, Ylr266, identified through yeast genome sequencing program. We constructed activated forms of the zinc finger (Zn(2)Cys(6)) protein Ylr266, and we analyzed the corresponding transcriptomes with DNA microarrays to characterize the up-regulated genes. The direct target genes of Ylr266 were further identified by in vivo chromatin immunoprecipitation procedure. The functions of the genes directly controlled by YLR266c are in agreement with the observed drug-resistance phenotype of the cell expressing an activated form of Ylr266. These target genes code for ATP-binding cassette or major facilitator superfamily transporters such as PDR15, YOR1, or AZR1 or for other proteins such as SNG1, YJL216c, or YLL056c which are already known to be involved in the yeast pleiotropic drug resistance (PDR) phenomenon. YLR266c could thus be named PDR8. Overlaps with the other PDR networks argue in favor of a new specific role for PDR8 in connection with the well known PDR regulators PDR1/PDR3 and YRR1. This strategy to identify the regulatory properties of an anonymous transcription factor is likely to be generalized to all the Zn(2)Cys(6) transcription factors from Saccharomyces cerevisiae and related yeasts.

The multidrug resistance transporters of the major facilitator superfamily, 6 years after disclosure of Saccharomyces cerevisiae genome sequence

The emergence of multidrug resistance (MDR) plays a crucial role in the failure of treatments of tumors and infectious diseases and in the control of plant pathogens, weeds and food-poisoning and food-spoilage microorganisms. Among the mechanisms underlying the MDR phenomenon in various organisms is the action of transmembrane transport proteins that presumably catalyse the active expulsion of structurally and functionally unrelated cytotoxic compounds out of the cell or their intracellular partitioning. On the basis of the complete genome sequence of Saccharomyces cerevisiae, numerous established and putative multidrug transporters were identified in this non-pathogenic, easy to manipulate eukaryotic model system. In yeast, the putative drug:H(+)-antiporters belong to the major facilitator superfamily; they comprise at least 23 proteins that have largely escaped characterisation by classical approaches. Other MDR determinants are membrane transporters belonging to the ATP binding cassette (ABC) superfamily, that utilize the energy of ATP hydrolysis for activity, and factors for transcriptional regulation of all the MDR transporters. This work reviews the current status of knowledge on the poorly characterized H(+)-antiporters, with 12 and 14 predicted spans, DHA12 and DHA14, drug efflux families. Consideration is given to the inventory and phylogenetic characterization, role as MDR determinants, regulation of gene expression, subcellular localisation and activity as solute transporters. Most of the present knowledge on these putative drug:H(+)-antiporters was driven by disclosure of S. cerevisiae genome sequence, in April 1996, being a paradigm of post-genomic research.

AQR1 gene (ORF YNL065w) encodes a plasma membrane transporter of the major facilitator superfamily that confers resistance to short-chain monocarboxylic acids and quinidine in Saccharomyces cerevisiae

We report results on the functional analysis of Saccharomyces cerevisiae ORF YNL065w, predicted to code for a protein belonging to the poorly characterized major facilitator superfamily (MFS) of transporters that are involved in multidrug resistance (MDR). YNL065w is important for a moderate increase of yeast tolerance to ketoconazole and to the cationic dye crystal violet; it protects the cell against short-chain monocarboxylic acids (C(2)-C(6)), but not against highly liposoluble acids such as octanoic acid or the phenoxyacetic-acid herbicides 2,4-D and MCPA; it is also a determinant of resistance to the antiarrhytmic and antimalarial drug quinidine. The encoding ORF was, thus, denominated the AQR1 gene. Results obtained using an AQR1-lacZ fusion indicate that gene expression is very low and it is not stimulated under weak acid stress. The encoded putative transporter was localized in the plasma membrane by fluorescence microscopy observation of the overproduced Aqr1-GFP fusion protein distribution.

New insights into the pleiotropic drug resistance network from genome-wide characterization of the YRR1 transcription factor regulation system

Yrr1p is a recently described Zn(2)Cys(6) transcription factor involved in the pleiotropic drug resistance (PDR) phenomenon. It is controlled in a Pdr1p-dependent manner and is autoregulated. We describe here a new genome-wide approach to characterization of the set of genes directly regulated by Yrr1p. We found that the time-course production of an artificial chimera protein containing the DNA-binding domain of Yrr1p activated the 15 genes that are also up-regulated by a gain-of-function mutant of Yrr1p. Gel mobility shift assays showed that the promoters of the genes AZR1, FLR1, SNG1, YLL056C, YLR346C, and YPL088W interacted with Yrr1p. The putative consensus Yrr1p binding site deduced from these experiments, (T/A)CCG(C/T)(G/T)(G/T)(A/T)(A/T), is strikingly similar to the PDR element binding site sequence recognized by Pdr1p and Pdr3p. The minor differences between these sequences are consistent with Yrr1p and Pdr1p and Pdr3p having different sets of target genes. According to these data, some target genes are directly regulated by Pdr1p and Pdr3p or by Yrr1p, whereas some genes are indirectly regulated by the activation of Yrr1p. Some genes, such as YOR1, SNQ2, and FLR1, are clearly directly controlled by both classes of transcription factor, suggesting an important role for the corresponding membrane proteins.

Saccharomyces cerevisiae resistance to chlorinated phenoxyacetic acid herbicides involves Pdr1p-mediated transcriptional activation of TPO1 and PDR5 genes

The transcription regulator Pdr1p is a determinant of Saccharomyces cerevisiae resistance to 2-methyl-4-chlorophenoxyacetic acid (MCPA) and 2,4-dichlorophenoxyacetic acid (2,4-D). The Pdr1p-regulated genes, TPO1 and PDR5, encoding putative multidrug transporters belonging to the major facilitator superfamily (MFS) and to the ATP-binding cassette (ABC) superfamily, respectively, are required for yeast resistance to sudden exposure to these herbicides. A rapid and transient activation of TPO1 (sixfold) and PDR5 (twofold) transcription takes place during the adaptation period preceding cell division under MCPA or 2,4-D moderate stress. These activations are mediated by both Pdr1p and Pdr3p and, as soon as adapted cells start duplication under herbicide stress, mRNA levels are drastically reduced to basal values. The longer duration of the adaptation period, observed for the Delta(pdr1) population, may involve the abolishment of the Pdr1p-mediated transcriptional activation of TPO1 and PDR5 genes, whose expression is critical to surpass the viability loss during the initial period of adaptation to the herbicides.