Histone protein surface accessibility dictates direction of RSC-dependent nucleosome mobilization

Area of Science:

• Molecular Biology
• Epigenetics
• Chromatin Dynamics

Background:

• Chromatin remodeling enzymes, like the RSC complex, use ATP hydrolysis to alter nucleosome structure and facilitate DNA accessibility.
• The precise mechanisms by which the RSC complex interacts with nucleosomes to achieve remodeling remain incompletely understood.

Purpose of the Study:

• To investigate the functional interaction between the RSC complex and specific nucleosome surfaces using a steric mapping approach.
• To elucidate how RSC activity, including nucleosome mobilization and DNA site exposure, is dependent on its binding orientation and access to nucleosomal components.

Main Methods:

• Utilized a steric mapping approach involving streptavidin binding to block specific nucleosome surfaces, including H2A N-terminal tails and regions near the acidic patch.
• Assessed RSC nucleosome mobilization and remodeling-dependent DNA site exposure using restriction enzyme accessibility assays.

Main Results:

• Blocking SHL ±4.5 on H2A N-terminal tails inhibited RSC nucleosome mobilization but not internal DNA site exposure.
• Complete occlusion of both nucleosome protein faces near the acidic patch abolished both mobilization and DNA site exposure.
• Partial inhibition upon single-face occlusion suggests RSC utilizes two productive binding orientations, with one being critical for mobilization.

Conclusions:

• Nucleosome mobilization by RSC necessitates access to the trailing protein surface, not the leading one.
• This study reveals a mechanism for RSC-mediated unidirectional nucleosome movement, crucial for regulating DNA sequences in vivo.