Single-molecule measurements reveal that PARP1 condenses DNA by loop stabilization

Area of Science:

• Molecular Biology
• Biophysics
• Genetics

Background:

• Poly(ADP-ribose) polymerase 1 (PARP1) is a key nuclear enzyme involved in DNA repair, transcription, and chromatin organization.
• While PARP1's role at DNA damage sites is well-studied, its interaction with undamaged DNA and impact on chromatin structure remain unclear.

Purpose of the Study:

• To investigate how PARP1 interacts with and organizes long, undamaged DNA molecules.
• To elucidate the mechanism by which PARP1 influences chromatin architecture.

Main Methods:

• Utilized single-molecule techniques to observe PARP1-DNA interactions under mechanical force.
• Performed stepwise decondensation and DNA braiding experiments to analyze DNA condensation activity.

Main Results:

• PARP1 binds to and condenses kilobase-length undamaged DNA under low mechanical forces (sub-piconewton).
• Condensation is mediated by PARP1 stabilizing DNA loops, as evidenced by decondensation at high force and braiding assays.
• PARP inhibitors did not affect undamaged DNA condensation but blocked reversal for damaged DNA with NAD+.

Conclusions:

• PARP1 actively organizes chromatin by condensing undamaged DNA through DNA loop stabilization.
• PARP1's function in chromatin organization may differ between undamaged and damaged DNA states.
• Findings propose a novel mechanism for PARP1 in shaping higher-order chromatin structure.