Mechanistic basis for selective Mediator-dependence of cell type-specifying transcription

ABSTRACT: The Mediator complex routes signals from DNA-binding transcription factors to RNA polymerase (Pol) II. Despite its pivotal position, mechanistic understanding of Mediator in human cells remains incomplete. Here, we quantified Mediator-controlled Pol II kinetics by coupling rapid subunit degradation with orthogonal experimental readouts. Consistent with a model of condensate-driven transcription initiation, large clusters of hypo-phosphorylated Pol II rapidly disassembled upon Mediator degradation. This was accompanied by a selective and pronounced disruption of cell type-specifying transcriptional circuits, whose constituent genes featured exceptionally high rates of Pol II turnover. Remarkably, transcriptional output of most other genes was largely unaffected by acute Mediator ablation. Maintenance of transcriptional activity at these genes was linked to an unexpected, CDK9-dependent compensatory feedback loop that elevated Pol II pause release rates genome-wide. Collectively, our work positions human Mediator as a globally acting coactivator that selectively safeguards the functionality of cell type-specifying transcriptional networks.

INSTRUMENT(S): Orbitrap Fusion Lumos

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Blood Cell, Cell Suspension Culture

DISEASE(S): Chronic Myeloid Leukemia

SUBMITTER: Martin Jaeger  

LAB HEAD: Georg E. Winter

PROVIDER: PXD017611 | Pride | 2021-09-08

REPOSITORIES: Pride