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TRANSCRIPTION FACTORS YAP1P AND PDR1P IN THE CONTROL OF MULTIDRUG RESISTANCE IN KLUYVEROMYCES LACTIS Svrbická A., Balážfyová Z., Tóth Hervay N., Gbelská Y. Department of Microbiology and Virology, Faculty of Natural Sciences, Comenius University in Bratislava, 842 15 Bratislava, Slovak Republic Multidrug resistance (MDR), known as pleiotropic drug resistance (PDR) is a ubiquitous cellular defence mechanism to deal with potential toxicity from environmental small molecular toxins or bioactives. The rapid induction of MDR in the model yeast Saccharomyces cerevisiae is controled by two networks of genes, YAP and PDR. In these networks two types of transcription factors are involved: with the structural motif of leucine zipper (bZIP) or zinc finger motifs Zn2Cys6, respectively. Many duplicated or multiplicated genes encoding transcriptional regulators in S. cerevisiae are present in fewer copies in Kluyveromyces lactis. Yap1p is a key determinant of oxidative stress response. It regulates expression of genes encoding proteins that maintain a favourable redox balance in the cell and proteins conferring metal and drug resistance. The main determinants of MDR in S. cerevisiae include the transcription factors Pdr1p and Pdr3p that control expression of ABC, MFS transporters and several other genes. KlPdr1p is the only homologue of ScPdr1p and ScPdr3p in K. lactis. In silico analysis of KlPDR1 gene promoter revealed the presence of one PDRE element and two YRE elements. In vitro binding of KlYap1p to the KlPDR1 promoter showed Hodúrová et al. (2011). In this work, we studied the mutual functional interaction between KlPdr1p and KlYap1p in more detail. We compared the sensitivity of standard strains and its isogenic deletion mutants (Klpdr1Δ, Klyap1Δ, Klpdr1Δyap1Δ) to antifungal azoles. Our results showed differences in strain´s susceptibilities to the cytotoxic drugs used. The influence of the transcription factors on the expression of the main ABC transporter gene KlPDR5 in K. lactis was also analysed. The activity of the reporter gene (promoter of KlPDR5 gene fused in frame with bacterial β-Dglucuronidase; PKlPDR5- gusA) was assessed together with the analysis of KlPDR5 gene expression in the strains studied using qPCR. Our results indicate that KlPdr1p influences the expression of KlPDR5 gene. Based on the results obtained, we propose that the transcription factor KlYap1p binds to the YRE elements present in the KlPDR1 gene promoter and controls the KlPDR5 gene expression. Further clarification of the relations between the main transcriptional regulators KlYap1p and KlPdr1p could help to understand the origin and the control of the multidrug resistance phenomenon in K. lactis yeast. Acknowledgments This work was supported by grants from the Slovak Grant Agency of Science (VEGA 1/0077/14 and 2/0111/15), the Slovak Research and Developmental Agency (APVV0282-10) and Comenius University (UK 246/2014). The contribution is also supported by the Research and Development Operational Programme funded by the ERDF (ITMS 26240220086). HODUROVA Z, TOTH HERVAY N, BALAZFYOVA Z, et al. 2011. Interplay among regulators of multidrug resistance in Kluyveromyces lactis. Gen Physiol Biophys 30:S1–92.