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Nature. 2019 Aug;572(7770):543-548. doi: 10.1038/s41586-019-1464-0. Epub 2019 Aug 7.

Pol II phosphorylation regulates a switch between transcriptional and splicing condensates.

Author information

1
Whitehead Institute for Biomedical Research, Cambridge, MA, USA.
2
Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, USA.
3
Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA.
4
Department of Physics, University of Illinois at Chicago, Chicago, IL, USA.
5
Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.
6
Institute of Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, MA, USA.
7
Computational Biology, St Jude Children's Research Hospital, Memphis, TN, USA.
8
Department of Biochemistry, University of Colorado, Boulder, CO, USA.
9
Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA, USA.
10
Whitehead Institute for Biomedical Research, Cambridge, MA, USA. young@wi.mit.edu.
11
Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, USA. young@wi.mit.edu.

Abstract

The synthesis of pre-mRNA by RNA polymerase II (Pol II) involves the formation of a transcription initiation complex, and a transition to an elongation complex1-4. The large subunit of Pol II contains an intrinsically disordered C-terminal domain that is phosphorylated by cyclin-dependent kinases during the transition from initiation to elongation, thus influencing the interaction of the C-terminal domain with different components of the initiation or the RNA-splicing apparatus5,6. Recent observations suggest that this model provides only a partial picture of the effects of phosphorylation of the C-terminal domain7-12. Both the transcription-initiation machinery and the splicing machinery can form phase-separated condensates that contain large numbers of component molecules: hundreds of molecules of Pol II and mediator are concentrated in condensates at super-enhancers7,8, and large numbers of splicing factors are concentrated in nuclear speckles, some of which occur at highly active transcription sites9-12. Here we investigate whether the phosphorylation of the Pol II C-terminal domain regulates the incorporation of Pol II into phase-separated condensates that are associated with transcription initiation and splicing. We find that the hypophosphorylated C-terminal domain of Pol II is incorporated into mediator condensates and that phosphorylation by regulatory cyclin-dependent kinases reduces this incorporation. We also find that the hyperphosphorylated C-terminal domain is preferentially incorporated into condensates that are formed by splicing factors. These results suggest that phosphorylation of the Pol II C-terminal domain drives an exchange from condensates that are involved in transcription initiation to those that are involved in RNA processing, and implicates phosphorylation as a mechanism that regulates condensate preference.

PMID:
31391587
PMCID:
PMC6706314
[Available on 2020-02-07]
DOI:
10.1038/s41586-019-1464-0

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