A role for the RNA Polymerase II-CTD phosphatase, FCP1 in the oxidative stress response

Fcp1 is a protein phosphatase that facilitates transcription elongation and termination by dephosphorylating the C-terminal domain of RNA Polymerase II. Here, we report an unanticipated role in the repression of the oxidative stress induced genes. High-throughput genetic and gene expression profiling of FCP1 mutants uncovered a link to Skn7, a key transcription factor in the oxidative stress response pathways, as well as a link to the Mediator complex kinase subunit, Cdk8. Interestingly, loss of CDK8 suppressed FCP1 mutant growth phenotypes upon exposure to oxidative stress, an effect dependent on SKN7. Furthermore, FCP1 and CDK8 regulated Skn7 protein levels and stability, as well as the expression of target genes through interdependent mechanisms. Focusing on the latter, while the FCP1 mutant robustly increased mRNA levels of Skn7-dependent genes under basal and induced conditions, it decreased Skn7 promoter occupancy, both defects normalized by loss of CDK8. Intriguingly, both FCP1 and CDK8 also altered Skn7 phosphorylation levels, a modification known to control Skn7 function, although the significance of this effect and residues involved remain unclear. Loss of CDK8 also alleviated the sensitivity of FCP1 mutants to other stressors, implicating these factors in regulating the response to other environmental insults. Microarray expression profiling was performed in duplicate. Cultures were grown in a 24-well plate incubator/reader to mid-log phase, with spiked-in RNA controls to monitor global changes in mRNA levels. Since no global changes in mRNA levels were detected, expression values were normalized to total mRNA levels. Fold changes were determined by comparing mutant to wild type profiles, with differentially expressed genes having a p-value <0.01 and absolute fold change >1.7 .