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Updated: Sep 14, 2025
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Author Spotlight: Evaluation of Protein-Condensate Dynamics in Live Human Cells
Published on: January 5, 2024
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Single-molecule live imaging of subunit interactions and exchange within cellular regulatory complexes
Thomas G W Graham1, Claire Dugast-Darzacq2, Gina M Dailey2
1Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA; Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, CA 94720, USA.
Molecular Cell
|July 24, 2025
Summary
New live-cell imaging reveals how positive transcription elongation factor b (P-TEFb) is regulated by protein-RNA interactions and chromatin binding, uncovering rapid feedback mechanisms.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Cells rely on complex molecular interaction networks.
- Understanding protein complex regulation in live cells is challenging.
Purpose of the Study:
- To investigate subunit interactions within endogenous protein complexes in live human cells.
- To elucidate the regulatory mechanisms of positive transcription elongation factor b (P-TEFb).
Main Methods:
- Proximity-assisted photoactivation (PAPA) combined with automated fast single-molecule tracking (fSMT).
- Live human cell imaging to observe molecular dynamics.
Main Results:
- The P-TEFb:7SK ribonucleoprotein complex is mobile and not chromatin-bound in its inactive state.
- hnRNPs interact with the 7SK complex, with binding modulated by Cdk9 inhibition.
- BRD4 enhances P-TEFb chromatin binding via its bromodomains.
- HIV Tat releases P-TEFb from 7SK.
Conclusions:
- P-TEFb regulation involves rapid, homeostatic negative feedback through competing protein-RNA interactions.
- BRD4 acts as a coactivator, influencing P-TEFb chromatin localization.
- P-TEFb release from 7SK by Tat highlights dynamic regulatory events.
