Comparison of transcriptional initiation by RNA polymerase II across eukaryotic species

  1. Natalia Petrenko
  2. Kevin Struhl  Is a corresponding author
  1. Harvard Medical School, United States


The preinitation complex (PIC) for transcriptional initiation by RNA polymerase (Pol) II is composed of general transcription factors that are highly conserved. However, analysis of ChIP-seq datasets reveals kinetic and compositional differences in the transcriptional initiation process among eukaryotic species. In yeast, Mediator associates strongly with activator proteins bound to enhancers, but it transiently associates with promoters in a form that lacks the kinase module. In contrast, in human, mouse, and fly cells, Mediator with its kinase module stably associates with promoters, but not with activator-binding sites. This suggests that yeast and metazoans differ in the nature of the dynamic bridge of Mediator between activators and Pol II and the composition of a stable inactive PIC-like entity. As in yeast, occupancies of TBP and associated factors (Tafs) at mammalian promoters are not strictly correlated. This suggests that within PICs, TFIID is not a monolithic entity, and multiple forms of TBP affect initiation at different classes of genes. TFIID in flies, but not yeast and mammals, interacts strongly at regions downstream of the initiation site, consistent with the importance of downstream promoter elements in that species. Lastly, Taf7 and the mammalian-specific Med26 subunit of Mediator also interact near the Pol II pause region downstream of the PIC, but only in subsets of genes and often not together. Species-specific differences in PIC structure and function are likely to affect how activators and repressors affect transcriptional activity.

Data availability

All datasets and their accession numbers are listed in Table 1.

Article and author information

Author details

  1. Natalia Petrenko

    Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, United States
    Competing interests
    No competing interests declared.
  2. Kevin Struhl

    Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, United States
    For correspondence
    Competing interests
    Kevin Struhl, Senior editor, eLife.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-4181-7856


National Institutes of Health (GM 30186)

  • Kevin Struhl

National Institutes of Health (GM 131801)

  • Kevin Struhl

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Reviewing Editor

  1. Naama Barkai, Weizmann Institute of Science, Israel

Version history

  1. Received: March 1, 2021
  2. Accepted: September 10, 2021
  3. Accepted Manuscript published: September 13, 2021 (version 1)
  4. Version of Record published: September 24, 2021 (version 2)


© 2021, Petrenko & Struhl

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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  1. Natalia Petrenko
  2. Kevin Struhl
Comparison of transcriptional initiation by RNA polymerase II across eukaryotic species
eLife 10:e67964.

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Further reading

    1. Chromosomes and Gene Expression
    Natalia Petrenko, Yi Jin ... Kevin Struhl
    Research Article Updated

    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.

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