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Cryo-EM structures of PRC2 simultaneously engaged with two functionally distinct nucleosomes.

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Polycomb repressive complex 2 (PRC2) uses nucleosomal DNA interactions to bind and methylate histone H3. This epigenetic mechanism facilitates gene silencing and heterochromatin formation.

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Area of Science:

  • Epigenetics
  • Molecular Biology
  • Structural Biology

Background:

  • Epigenetic regulation involves protein complexes that modify chromatin.
  • Polycomb repressive complex 2 (PRC2) is a key gene silencer, methylating histone H3 at lysine 27 (H3K27me).
  • PRC2 activity is enhanced by its product and dinucleosomes, promoting H3K27me spreading and gene repression.

Purpose of the Study:

  • To elucidate the structural basis of PRC2 interaction with dinucleosomes.
  • To understand how PRC2 recognizes and is activated by its chromatin substrate.
  • To reveal the mechanism of H3K27 methylation spreading.

Main Methods:

  • Cryo-electron microscopy (cryo-EM) reconstructions.
  • Structural analysis of human PRC2 bound to bifunctional dinucleosomes.
  • Biochemical assays to study PRC2 activity and interactions.

Main Results:

  • Cryo-EM structures reveal how PRC2 binds dinucleosomes via nucleosomal DNA.
  • PRC2 positions H3 tails from both nucleosomes for interaction with EED and EZH2.
  • The structure accommodates varying linker DNA lengths, explaining PRC2's flexibility.

Conclusions:

  • PRC2 utilizes specific DNA interactions to engage complex chromatin substrates.
  • Structural insights explain PRC2's auto-stimulation and substrate preference.
  • This mechanism is crucial for epigenetic gene silencing and heterochromatin formation.