Nucleated transcriptional condensates amplify gene expression.

Area of Science:

• Cell Biology
• Molecular Biology
• Biophysics

Background:

• Membraneless organelles, or condensates, form via liquid-liquid phase separation.
• Transcriptional condensates are hypothesized to regulate gene expression at specific genomic loci.
• Direct biophysical evidence linking phase separation to dynamic gene transcription in living cells is limited.

Purpose of the Study:

• To investigate the role of FET-family proteins in phase separation and transcriptional regulation within living cells.
• To explore the biophysical mechanisms underlying condensate formation and gene expression.
• To establish a direct link between phase separation and dynamic transcriptional output.

Main Methods:

• Utilized an optogenetic approach to study FET-family protein behavior in living cells.
• Analyzed the charge distribution of FET family members, focusing on TAF15.
• Investigated the interaction between TAF15 and the C-terminal domain of RNA polymerase II.
• Examined condensate nucleation at genomic loci and recruitment of RNA polymerase II.

Main Results:

• FET-family transcriptional regulators demonstrate a propensity for phase separation in living cells.
• TAF15's unique charge distribution facilitates enhanced interaction with RNA polymerase II's C-terminal domain.
• Clusters of RNA polymerase II C-terminal domains at genomic loci reduce the energy barrier for TAF15 condensate nucleation.
• TAF15 condensates recruit additional RNA polymerase II, leading to amplified transcriptional output.

Conclusions:

• Phase separation of FET proteins, particularly TAF15, plays a direct role in driving localized RNA transcription.
• Positive feedback loops between interacting transcriptional components promote localized phase separation.
• This mechanism amplifies gene expression by concentrating the necessary molecular machinery at specific genomic sites.