Atomic Force Microscopy Analysis of Bridging-Induced Phase Separation Mediated by SMC Proteins

Area of Science:

• Molecular Biology
• Genetics
• Biophysics

Background:

• Structural maintenance of chromosome (SMC) proteins are crucial for genome stability and chromosomal organization.
• SMC complexes like cohesin typically organize DNA through loop extrusion.
• Recent studies suggest an alternative mechanism: bridging-induced phase separation (BIPS).

Purpose of the Study:

• To present a detailed protocol for exploring BIPS in cohesin/DNA condensates using atomic force microscopy (AFM).
• To facilitate the investigation of ATP-independent DNA-bridging-dependent condensate formation.
• To provide insights into the molecular mechanisms of DNA/protein co-condensation.

Main Methods:

• Atomic Force Microscopy (AFM) for high-resolution imaging of protein-DNA interactions.
• Detailed protocol for AFM image acquisition.
• Comprehensive data analysis strategies for AFM datasets.

Main Results:

• Demonstration of a robust protocol for visualizing cohesin/DNA condensates.
• Characterization of BIPS as a mechanism for SMC protein-mediated DNA organization.
• Validation of ATP-independent condensate formation.

Conclusions:

• The presented AFM protocol enables detailed study of BIPS in cohesin/DNA systems.
• BIPS offers a new perspective on SMC protein function in genome organization.
• This methodology can be extended to investigate other DNA-binding proteins involved in phase separation.