Regulation of the pleiotropic drug resistance transcription factors Pdr1 and Pdr3 in yeast

Aim: To understand how transcriptional factors Pdr1 and Pdr3, belonging to the pleiotropic drug resistance system, are activated, and regulated after introducing chemical tox- ins to the cell in the model organism Saccharomyces cere-visiae. Methods: Series of molecular methods were applied using different strains ofS. cerevisiae over-expressing proteins of interest as a eukaryotic cell model. The chemical stress in- troduced to the cell is represented by menadione. Results were obtained performing protein detection and analysis. Additionally, the regulation of the DNA binding of the tran- scriptional activators after stimulation is quantified using chromatin immunoprecipitation, employing epitope-tagged factors and real-time qPCR. Results: Our results indicated higher expression levels of the Pdr1 transcriptional factor, compared to its homolo- gous Pdr3 after treatment with menadione. The yeast-cell defence system was tested against various organic solvents to exclude the possibility of their presence potentially af- fecting the results. The results indicate that Pdr1 is most abundant after 30 minutes from the beginning of the treat- ment, compared with 240 minutes after the treatment when the function of the transcription factor is faded. It appears that Pdr1 binding to the PDR5 and SNQ2 promoters, which are both activated by Pdr1, peaks around the same time, or more precisely after 40 minutes from the start of the treatment. Conclusion: The tendency of Pdr1 reduction after its activa- tion by menadione is detected. One possibility is that Pdr1, after recognizing the xenobiotic menadione, is removed by a degradation mechanism. Given the fact that Pdr1 directly binds the xenobiotic molecule, its destruction might help the cells to remove toxic levels of menadione. It is possible that overexpressing the part of Pdr1 which recognizes me- nadione alone was sufficient to detoxify and hence produce a tolerance towards menadione.