module: dmel_mitochondrial_dna_replisome
title: Mitochondrial DNA replisome in Drosophila melanogaster
label: Mitochondrial DNA replisome
module_type: PROTEIN_COMPLEX
description: >-
  Mitochondrial DNA is copied by a dedicated replisome in the mitochondrial
  matrix that is separate from the nuclear replication machinery. DNA
  polymerase gamma, a heterodimer of the catalytic subunit PolG1 and the
  accessory subunit PolG2, synthesizes DNA and proofreads it. The
  mitochondrial replicative helicase (mtDNA-helicase, the ortholog of human
  Twinkle) unwinds the duplex ahead of the polymerase, and the mitochondrial
  single-stranded DNA-binding protein mtSSB coats the displaced strand and
  stimulates both enzymes. Mutations in these genes in Drosophila reduce
  mtDNA copy number.
summary: >-
  Pol gamma, the Twinkle-family helicase and mtSSB that together replicate
  mitochondrial DNA.
concepts:
  - {id: GO:0030894, label: replisome}
cellular_components:
  - {id: GO:0042645, label: mitochondrial nucleoid}
parts:
  - id: pol_gamma
    label: DNA polymerase gamma
    role: mitochondrial DNA polymerase
    genes: [PolG1, PolG2]
    complex_term: {id: GO:0005760, label: gamma DNA polymerase complex}
    unit_functions:
      PolG1: {id: GO:0003887, label: DNA-directed DNA polymerase activity}
    processes:
      - {id: GO:0006264, label: mitochondrial DNA replication}
  - id: mtdna_helicase
    label: Mitochondrial replicative helicase
    role: replicative helicase
    genes: [mtDNA-helicase]
    function: {id: GO:0043139, label: "5'-3' DNA helicase activity"}
    processes:
      - {id: GO:0006264, label: mitochondrial DNA replication}
  - id: mtssb
    label: Mitochondrial single-stranded DNA-binding protein
    role: single-stranded DNA protection
    genes: [mtSSB]
    function: {id: GO:0003697, label: single-stranded DNA binding}
    processes:
      - {id: GO:0006264, label: mitochondrial DNA replication}
connections:
  - {source: mtdna_helicase, target: pol_gamma, connection_type: PROVIDES_INPUT_FOR, description: The helicase unwinds the template that Pol gamma copies.}
  - {source: mtssb, target: pol_gamma, connection_type: POSITIVELY_REGULATES, description: mtSSB coats displaced single strands and stimulates DNA synthesis.}
notes: >-
  Pol gamma also appears as a part of dmel_dna_polymerase_complexes. The
  5'-3' helicase activity is assigned to mtDNA-helicase by conservation with
  human Twinkle. Mitochondrial RNA polymerase (primer synthesis),
  topoisomerases and TFAM are outside the module.