The Kinase Module of the Mediator regulates cell cycle re-entry and transcriptional response following DNA damage

When faced with a DNA double strand break, cells activate an elaborate signaling cascade called the DNA damage response to protect genomic integrity. To identify novel factors that modulate the DNA damage response to DNA double strand breaks, we performed an epistatic miniarray profile (E-MAP) analysis of Mec1 and Rad53, two essential kinases that coordinate the DNA damage response in budding yeast. Through this analysis, we discovered a genetic interaction between the kinase module (CKM) of the Mediator of transcription and Rad53. We find that all four subunits of the CKM, as well as CKM’s kinase activity are critical for cell cycle re-entry following a DNA break, whereas the core Mediator subunits are dispensable. Notably, CKM mutants do not impair DNA repair by homologous recombination or confer sensitivity to DNA damaging reagents, suggesting that CKM specifically impinges on DNA damage signaling. In support of this, we find that Rad53 and CKM physically interact in response to DNA damage. Following the induction of a DNA break, CKM is a critical regulator of global transcription inhibition. In addition to this global effect, we illustrate that CKM functions locally at DNA breaks together with the core Mediator. In the absence of catalytically active CKM, the CKM-Mediator complexes at DNA breaks are replaced by RNAPII. Taken together, our results reveal a previously uncharacterized role for CKM in the DNA damage response. ### Competing Interest Statement The authors have declared no competing interest.