Gene Regulation
Role for the MED21-MED7 Hinge in Assembly of the Mediator-RNA Polymerase II Holoenzyme
Mediator plays an integral role in activation of RNA polymerase II (Pol II) transcription. A key step in activation is binding of Mediator to Pol II to form the Mediator-Pol II holoenzyme. Here, we exploit a combination of biochemistry and macromolecular EM to investigate holoenzyme assembly. We identify a subset of human Mediator head module subunits that bind Pol II independent of other subunits and thus probably contribute to a major Pol II binding site. In addition, we show that binding of human Mediator to Pol II depends on the integrity of a conserved “hinge” in the middle module MED21-MED7 heterodimer.Assembly of the Elongin A Ubiquitin Ligase Is Regulated by Genotoxic and Other Stresses
Background: Elongin is both a Pol II elongation factor and part of a ubiquitin ligase targeting stalled Pol II.Results: Elongin ubiquitin ligase assembly is driven by signals that provoke Pol II stalling and/or activate Elongin-dependent transcription.Conclusion: Elongin ligase assembly is a regulated process.Significance: This study provides insight into Elongin ubiquitin ligase functions and general mechanisms of ubiquitin ligase activation.
