GSE129898
The polymorphic PolyQ tail protein of the Mediator Complex, Med15, regulates variable response to stress
The Mediator is composed of multiple of proteins in the head, body, tail and CDK subunits conserved from yeast to humans. However, not all the components are required for transcription. Components of the tail subunit are not essential but to varying degrees are required for changes in transcription to stress. While some stresses are familiar such as heat, desiccation, and starvation, others are exotic yet elicit a physical stress response. MCHM is a hydrotrope that induces growth arrest in yeast. By exploiting genetic variation, specifically in Med15, between yeast strains, we found that Med15 with the polyQ expansion conferred MCHM sensitivity. This sensitivity was not from a loss of function as the reciprocal hemizygous hybrids were all sensitive, suggesting that there is an incompatibility between Mediator complexes from genetic divergent yeast strains. Transcriptomics from yeast expressing the incompatible Med15 changed expression in diverse pathways. Expansion of polyQ tracts in Med15 resulted in multiple isoforms which were mostly from likely post-translational modifications. Stability of Med15 was dependent on Ydj1, a chaperone and the incompatible Med15 allele was expressed at lower levels and less stable than the compatible Med15 allele. Med15 is tethered to the rest of the Mediator complex via Med2 and 3. Deletion of either Med2 or Med3 changes the Med15 isoform patterns in the in a similar manner whereas deletion of Med5, a distal component of the tail did not change the pattern. The med2 and 3 mutants are similarly sensitive to MCHM while med5 mutants are not. Differences between the Med15 alleles extend to responses to different stresses. Whereas the incompatible allele of Med15 improved growth to chemicals that produce free radicals, and the compatible allele of Med15 improved growth to reducing agents, caffeine, and hydroxyurea. This may reflect the positive and negative role that Med15 has in transcription. Overall design: mRNA profiles of med15 knockout and mutants in a BY4741 background, in YPD or YM, treated or not with MCHM, in triplicate, using Illumina Miseq.