The Effect of MCHM on Stress Response Pathway Regulators, Med15 and Snf1

In 2014, large volumes of MCHM (4-methylcyclohexane) spilled into the Elk River of West Virginia contaminating drinking-water supplies. By studying cellular stress response through the Mediator complex in Saccharomyces cerevisiae(baker’s yeast), the molecular effects of the industrial coal-cleaning chemical can be determined. Mediator, a highly conserved multi subunit complex relays signals from DNA binding transcription factors to RNA polymerase II. Med15, a subunit found within the tail domain of the Mediator complex works with stress-induced transcription factors and is regulated by many kinases including CDKs and the AMP kinase Snf1. Because Snf1 interacts with the Mediator complex and is required for many cellular activities such as glucose-repressed gene transcription and pH tolerance. snf1∆ yeasts are much more sensitive to MCHM compared to wild-type. Genetic variation in terms of polyQ tracts between yeast strains (YJM789 and S288c) exhibit varying tolerance to MCHM and other chemical stressors. A C-terminal Myc tag has an impact on Med15 and its sensitivity to MCHM. There are multiple isoforms of Med15-Myc tag protein detected on a western blot and the levels of the Med15 protein differ based on the alleles and the presence of Snf1 and Reg1 (negative regulator of Snf1).