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The exonuclease activity of DNA polymerase γ is required for ligation during mitochondrial DNA replication

Lookup NU author(s): Dr Jim StewartORCiD



This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


Mitochondrial DNA (mtDNA) polymerase γ (POLγ) harbours a 3′–5′ exonuclease proofreading activity. Here we demonstrate that this activity is required for the creation of ligatable ends during mtDNA replication. Exonuclease-deficient POLγ fails to pause on reaching a downstream 5′-end. Instead, the enzyme continues to polymerize into double-stranded DNA, creating an unligatable 5′-flap. Disease-associated mutations can both increase and decrease exonuclease activity and consequently impair DNA ligation. In mice, inactivation of the exonuclease activity causes an increase in mtDNA mutations and premature ageing phenotypes. These mutator mice also contain high levels of truncated, linear fragments of mtDNA. We demonstrate that the formation of these fragments is due to impaired ligation, causing nicks near the origin of heavy-strand DNA replication. In the subsequent round of replication, the nicks lead to double-strand breaks and linear fragment formation.

Publication metadata

Author(s): Macao B, Uhler JP, Siibak T, Zhu X, Shi Y, Sheng W, Olsson M, Stewart JB, Gustafsson CM, Falkenberg M

Publication type: Article

Publication status: Published

Journal: Nature Communications

Year: 2015

Volume: 6

Online publication date: 22/06/2015

Acceptance date: 27/04/2015

Date deposited: 21/12/2020

ISSN (electronic): 2041-1723

Publisher: Nature Research


DOI: 10.1038/ncomms8303

PubMed id: 26095671


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