module: dmel_polycomb_group_complexes
title: Polycomb group repressive complexes in Drosophila melanogaster
label: Polycomb group complexes
module_type: PROTEIN_COMPLEX
description: >-
  Polycomb group (PcG) proteins maintain the repressed state of developmental
  regulators such as the Hox genes through cell divisions. They act through
  several distinct complexes recruited to Polycomb response elements (PREs).
  PRC2 trimethylates histone H3 lysine 27 through the E(z) methyltransferase.
  PRC1 binds H3K27me3 through the Polycomb chromodomain and compacts chromatin.
  dRAF and the variant PRC1-like complexes monoubiquitylate histone H2A
  lysine 118 through the Sce (dRing) E3 ligase. PhoRC, built around the
  sequence-specific DNA-binding protein Pho (or its paralog Phol) and Sfmbt,
  helps target PcG complexes to PREs. PR-DUB, formed by Calypso and Asx,
  removes H2A ubiquitin.
summary: >-
  PcG complexes (PRC1, PRC2, PhoRC, PR-DUB, dRAF and variant PRC1) that
  establish and maintain Polycomb silencing at PREs.
concepts:
  - {id: GO:0031519, label: PcG protein complex}
cellular_components:
  - {id: GO:0000785, label: chromatin}
parts:
  - id: prc2
    label: Polycomb repressive complex 2
    role: H3K27 methyltransferase complex
    description: >-
      E(z)-containing complex that trimethylates H3K27. FlyBase distinguishes a
      Pcl-containing variant and a Jarid2-Jing variant.
    complex_term: {id: GO:0035098, label: ESC/E(Z) complex}
    variant_sets:
      - id: prc2_variants
        label: PRC2 accessory-subunit variants
        selection: ONE_OR_MORE
        variants:
          - {id: prc2_pcl, label: PRC2 Pcl variant, group: PRC2, complex_term: {id: GO:0035098, label: ESC/E(Z) complex}, unit_functions: {E(z): {id: GO:0046976, label: histone H3K27 methyltransferase activity}}}
          - {id: prc2_jarid2_jing, label: PRC2 Jarid2-Jing variant, group: PRC2-JJ, complex_term: {id: GO:0035098, label: ESC/E(Z) complex}, unit_functions: {E(z): {id: GO:0046976, label: histone H3K27 methyltransferase activity}}}
  - id: prc1
    label: Polycomb repressive complex 1
    role: H3K27me3 reader and chromatin compaction complex
    variant_sets:
      - id: prc1_variants
        label: PRC1 Psc or Su(z)2 variants
        selection: ONE_OR_MORE
        variants:
          - {id: prc1_psc, label: PRC1 Psc variant, group: PRC1, complex_term: {id: GO:0035102, label: PRC1 complex}, unit_functions: {Sce: {id: GO:0061630, label: ubiquitin protein ligase activity}}}
          - {id: prc1_suz2, label: PRC1 Su(z)2 variant, group: PRC1-VAR, complex_term: {id: GO:0035102, label: PRC1 complex}, unit_functions: {Sce: {id: GO:0061630, label: ubiquitin protein ligase activity}}}
  - id: h2a_ubiquitylation_complexes
    label: H2A ubiquitylating variant PRC1 complexes
    role: H2AK118 monoubiquitylation
    variant_sets:
      - id: vprc1_variants
        label: dRing-containing H2A ubiquitin ligase complexes
        selection: ONE_OR_MORE
        variants:
          - {id: draf, label: dRING-associated factors complex, group: DRAF, unit_functions: {Sce: {id: GO:0061630, label: ubiquitin protein ligase activity}, Kdm2: {id: GO:0051864, label: histone H3K36 demethylase activity}}}
          - {id: bcorl_siesta_ring1, label: BCORL-Siesta-RING1 complex, group: VPRC1-1, unit_functions: {Sce: {id: GO:0061630, label: ubiquitin protein ligase activity}, Kdm2: {id: GO:0051864, label: histone H3K36 demethylase activity}}}
          - {id: tay_siesta_ring1, label: Tay-Siesta-RING1 complex, group: VPRC1-3-5, unit_functions: {Sce: {id: GO:0061630, label: ubiquitin protein ligase activity}}}
  - id: phorc
    label: Pho repressive complex
    role: PRE targeting
    variant_sets:
      - id: phorc_variants
        label: Pho or Phol PhoRC
        selection: ONE_OR_MORE
        variants:
          - {id: phorc_pho, label: PhoRC Pho variant, group: PHORC}
          - {id: phorc_phol, label: PhoRC Phol variant, group: PHORC-L}
  - id: pr_dub
    label: Polycomb repressive deubiquitinase
    role: H2A deubiquitylation
    group: PR-DUB
    complex_term: {id: GO:0035517, label: PR-DUB complex}
    unit_functions:
      caly: {id: GO:0004843, label: cysteine-type deubiquitinase activity}
  - id: pcg_recruiters
    label: Polycomb group recruiters and DNA-binding proteins
    role: PRE-binding recruiters
    description: Sequence-specific DNA-binding proteins that FlyBase groups as PcG recruiters.
    group: PCG-DNA
    complex: false
function_note: >-
  Catalytic subunits carry the complexes' enzymatic activities, each with GOA
  support for the fly protein: E(z) histone H3K27 methyltransferase activity
  in both PRC2 variants (GO:0046976; IDA, IMP, IBA), Sce (dRing) ubiquitin
  protein ligase activity in every Sce-containing PRC1 and variant PRC1
  complex (GO:0061630; IMP, IBA), Kdm2 histone H3K36 demethylase activity in
  the Kdm2-containing complexes (GO:0051864; IMP, IBA), and Calypso
  cysteine-type deubiquitinase activity in PR-DUB (GO:0004843; IDA, EXP).
  Reader and DNA-binding subunits (Pc, Pcl, Sfmbt, Pho, Phol) are not given
  binding terms as their annoton function.