PAR-Driven Condensation Maintains Stalled Replication Fork Stability

Area of Science:

• Cell Biology
• Biochemistry
• Genomics

Background:

• Poly(ADP-ribose) (PAR) is a nucleic acid-like polymer involved in cellular events.
• PAR polymerases (PARPs) catalyze PAR formation as a post-translational modification.
• Liquid-liquid phase separation (LLPS) generates functional subcellular condensates.

Purpose of the Study:

• To investigate the role of PAR in biomolecular condensation.
• To identify cellular conditions and factors influencing PAR condensation.
• To understand the functional implications of PAR condensation in stressed cells.

Main Methods:

• Imaging-based screening of small molecules.
• Proteasome inhibition in various cell types.
• Co-localization studies of PAR, proteasome, and ubiquitin chains.
• Assessment of DNA replication fork stability.

Main Results:

• PAR undergoes LLPS upon proteasome inhibition, forming nuclear condensates.
• These condensates involve PAR, proteasome, and ubiquitin chains, dependent on PARP2 and K6-linked ubiquitylation.
• PAR directly interacts with ubiquitin chains for the first time.
• Stalled DNA replication forks co-localize with these condensates.

Conclusions:

• PAR condensation is a novel self-protective mechanism in cells under proteasomal stress.
• PAR-proteasome-ubiquitin chain condensates stabilize stalled replication forks, maintaining genomic integrity.
• This study provides fundamental insights into PAR condensation and its cellular functions.