Evidence that Mediator is essential for Pol II transcription, but is not a required component of the preinitiation complex in vivo
Abstract
The Mediator complex has been described as a general transcription factor, but it is unclear if it is essential for Pol II transcription and/or is a required component of the preinitiation complex (PIC) in vivo. Here, we show that depletion of individual subunits, even those essential for cell growth, causes a general but only modest decrease in transcription. In contrast, simultaneous depletion of all Mediator modules causes a drastic decrease in transcription. Depletion of head or middle subunits, but not tail subunits, causes a downstream shift in the Pol II occupancy profile, suggesting that Mediator at the core promoter inhibits promoter escape. Interestingly, a functional PIC and Pol II transcription can occur when Mediator is not detected at core promoters. These results provide strong evidence that Mediator is essential for Pol II transcription and stimulates PIC formation, but it is not a required component of the PIC in vivo.
Data availability
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Mediator is essential for Pol II transcription, but is not a required component of the preinitiation complexPublicly available at NCBI Gene Expression Omnibus (accession no. GSE93190).
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Saccharomyces cerevisiae S288c Genome sequencingPublicly available via DNA Data Bank of Japan (accession no. SRP047524).
Article and author information
Author details
Funding
National Institutes of Health (GM 30186)
- Kevin Struhl
Croucher Foundation
- Koon Ho Wong
University of Macau (MYRG2015-00186-FHS)
- Koon Ho Wong
University of Macau (MYRG2016-0-0211-FHS)
- Koon Ho Wong
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Reviewing Editor
- Alan G Hinnebusch, National Institutes of Health, United States
Version history
- Received: December 24, 2016
- Accepted: July 9, 2017
- Accepted Manuscript published: July 12, 2017 (version 1)
- Version of Record published: July 26, 2017 (version 2)
- Version of Record updated: September 18, 2017 (version 3)
Copyright
© 2017, Petrenko et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Further reading
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- Chromosomes and Gene Expression
- Developmental Biology
Developmental programming involves the accurate conversion of signalling levels and dynamics to transcriptional outputs. The transcriptional relay in the Notch pathway relies on nuclear complexes containing the co-activator Mastermind (Mam). By tracking these complexes in real time, we reveal that they promote the formation of a dynamic transcription hub in Notch ON nuclei which concentrates key factors including the Mediator CDK module. The composition of the hub is labile and persists after Notch withdrawal conferring a memory that enables rapid reformation. Surprisingly, only a third of Notch ON hubs progress to a state with nascent transcription, which correlates with polymerase II and core Mediator recruitment. This probability is increased by a second signal. The discovery that target-gene transcription is probabilistic has far-reaching implications because it implies that stochastic differences in Notch pathway output can arise downstream of receptor activation.