Tail and Kinase Modules Differently Regulate Core Mediator Recruitment and Function In Vivo

Mediator is a highly conserved transcriptional coactivator organized into four modules, namely Tail, Middle, Head, and Kinase (CKM). Previous work suggests regulatory roles for Tail and CKM, but an integrated model for these activities is lacking. Here, we analyzed the genome-wide distribution of Mediator subunits in wild-type and mutant yeast cells in which RNA polymerase II promoter escape is blocked, allowing detection of transient Mediator forms. We found that although all modules are recruited to upstream activated regions (UAS), assembly of Mediator within the pre-initiation complex is accompanied by the release of CKM. Interestingly, our data show that CKM regulates Mediator-UAS interaction rather than Mediator-promoter association. In addition, although Tail is required for Mediator recruitment to UAS, Tailless Mediator nevertheless interacts with core promoters. Collectively, our data suggest that the essential function of Mediator is mediated by Head and Middle at core promoters, while Tail and CKM play regulatory roles. [Display omitted] •A dynamic model for Mediator module interactions with genes•CKM is release upon integration of Mediator into the pre-initiation complex•Mediator can integrate the PIC without prior recruitment to UAS by the Tail module•CKM regulates Mediator-UAS interactions rather than Mediator-PIC association Jeronimo et al. describe a dynamic model for the interaction of Mediator modules with genes. CKM negatively regulates Mediator-UAS interactions and dissociates from Mediator upon integration of Mediator into the PIC. Tailless Mediator integrates PIC through an alternative pathway.