Inseparable RNA binding and chromatin modification activities of a nucleosome-interacting surface in EZH2.

Area of Science:

• Epigenetics
• Molecular Biology
• Gene Regulation

Background:

• Polycomb repressive complex 2 (PRC2) is essential for maintaining transcription programs in differentiated cells.
• The interaction between PRC2 and RNA is known, but its regulatory role in PRC2 functions remains unclear.
• PRC2's canonical functions include chromatin modification, specifically histone methylation.

Purpose of the Study:

• To investigate the role of RNA binding in PRC2's chromatin modification and gene repression activities.
• To determine whether RNA binding itself or other functions of the RNA-binding surface regulate PRC2.
• To elucidate the mechanism by which RNA binding influences PRC2's enzymatic activity.

Main Methods:

• Utilized separation-of-function mutants of EZH2, the catalytic subunit of PRC2.
• Assayed mutants defective in RNA binding but retaining methyltransferase activity.
• Performed in vitro and in-cell assays to assess chromatin modification and gene repression activities.

Main Results:

• A specific region on the EZH2 RNA-binding surface is required for chromatin modification, independent of RNA binding.
• This surface interacts with nucleosomal DNA, mediating chromatin modification in vitro and in cells.
• An RNA-binding-defective mutant showed normal chromatin modification and gene repression in lineage-committed cells.

Conclusions:

• The RNA-binding surface of EZH2, not RNA binding per se, is critical for histone methylation.
• Interactions with nucleosomal DNA via the EZH2 RNA-binding surface are essential for chromatin modification.
• PRC2's function in maintaining transcription programs is regulated by its interaction with chromatin, independent of direct RNA interaction.