| dc.description.abstract | Mediator is a protein complex in eukaryotes which integrates signals from a diverse range of transcription factors and relays them to RNA polymerase. Much of mediator is highly conserved, but it is expected that some sequences would become specialized according to the regulatory needs of particular organisms. Since the ability to tolerate high concentrations of ethanol is a characteristic feature of Saccharomyces cerevisiae, we studied mediator structure/function relationships through growth analysis of mutants on 2% glucose ± 6% ethanol. From this work, we identified a 35 amino acid sequence within Med8 in the "neck" region of the head module that plays a key role in ethanol tolerance under certain conditions, but which has little impact on growth on 2% glucose alone. Surprisingly, this region was only required for ethanol tolerance when the sequences that tether Med18 & Med20 to the head module were deleted or when the nearby Med31 subunit was deleted. Based on cryo-EM, these are both conditions which induce flexibility of the head module. Our working model is that this region of the mediator "neck" stabilizes a conformation of the mediator complex which is necessary for appropriate expression of key genes that confer ethanol tolerance, but which is not necessary for growth on glucose without ethanol. This is likely due to gene and context-specific changes in the structure and activity of the adjacent RNA polymerase CTD binding region. | en |
