Polycomb group targeting through different binding partners of RING1B C-terminal domain

Area of Science:

• Epigenetics and Chromatin Biology
• Molecular and Cellular Biology
• Developmental Biology

Background:

• Polycomb Group (PcG) proteins regulate gene expression by modifying chromatin.
• RING1B, a core PcG protein, is known to bind methylated chromatin via Polycomb (Pc).
• RING1B's association with non-methylated chromatin suggests alternative interaction mechanisms.

Purpose of the Study:

• To investigate the alternative mechanisms of RING1B interaction with chromatin.
• To identify proteins that bind RING1B independently of methylated chromatin.
• To elucidate the structural basis and functional significance of these interactions.

Main Methods:

• Protein-protein interaction studies using the C-terminal domain of RING1B (C-RING1B).
• Structural analysis of C-RING1B in complex with Pc cbox domain and RYBP.
• Mutational analysis of Drosophila dRING1 to assess in vivo function.

Main Results:

• RYBP and the Pc cbox domain bind to the same surface on C-RING1B.
• Both proteins form a similar intermolecular beta sheet with C-RING1B but possess distinct loop structures.
• Both the beta sheet and loop are essential for stable binding and transcriptional repression.
• A mutation disrupting binding in Drosophila dRING1 impaired chromatin association and PcG function.

Conclusions:

• PcG targeting to chromatin involves diverse binding partners of RING1B.
• These partners exhibit sequence and structural diversity.
• This diversity contributes to the specific targeting of PcG complexes to different chromatin locations.