Dynamics of nucleosome remodelling by individual ACF complexes

Area of Science:

• Chromatin biology
• Molecular mechanisms of gene regulation
• Nucleosome dynamics

Background:

• The ATP-dependent chromatin assembly and remodelling factor (ACF) is crucial for generating regularly spaced nucleosomes, essential for heritable gene silencing.
• The precise mechanism by which ACF mobilizes nucleosomes remains largely unelucidated.

Purpose of the Study:

• To investigate the real-time dynamics and intermediates of nucleosome remodelling by ACF using single-molecule Förster Resonance Energy Transfer (FRET).
• To elucidate the distinct roles of ATP hydrolysis in the nucleosome remodelling process mediated by ACF.

Main Methods:

• Single-molecule Förster Resonance Energy Transfer (smFRET) was employed to monitor individual nucleosome remodelling events by ACF in real time.
• Kinetic analysis was performed to identify intermediate states and translocation steps during ACF-mediated nucleosome movement.

Main Results:

• ACF-mediated nucleosome translocation along DNA occurs in gradual steps, characterized by well-defined kinetic pauses after approximately 7 or 3-4 base pairs of movement.
• ATP hydrolysis is essential for ACF binding, DNA translocation, and the release from kinetic pauses, highlighting three distinct ATP-dependent functions.
• ACF exhibits high processivity and bidirectionality, capable of repeatedly translocating nucleosomes back and forth before dissociation.

Conclusions:

• ACF functions as a processive and bidirectional nucleosome translocase, with ATP hydrolysis driving key steps in the remodelling cycle.
• The study reveals novel intermediates and dynamics in ACF-mediated nucleosome remodelling, advancing our understanding of chromatin dynamics and gene silencing mechanisms.