Expression of catalytic mutants of the mtDNA helicase Twinkle and polymerase POLG causes distinct replication stalling phenotypes

Sjoerd Wanrooij, Steffi Goffart, Jaakko L.O. Pohjoismäki, Takehiro Yasukawa, Johannes N. Spelbrink

Research output: Contribution to journalArticlepeer-review

104 Citations (Scopus)

Abstract

The mechanism of mitochondrial DNA replication is a subject of intense debate. One model proposes a strand-asynchronous replication in which both strands of the circular genome are replicated semi-independently while the other model proposes both a bidirectional coupled leading- and lagging-strand synthesis mode and a unidirectional mode in which the lagging-strand is initially laid-down as RNA by an unknown mechanism (RITOLS mode). Both the strand-asynchronous and RITOLS model have in common a delayed synthesis of the DNA-lagging strand. Mitochondrial DNA is replicated by a limited set of proteins including DNA polymerase gamma (POLG) and the helicase Twinkle. Here, we report the effects of expression of various catalytically deficient mutants of POLG1 and Twinkle in human cell culture. Both groups of mutants reduced mitochondrial DNA copy number by severe replication stalling. However, the analysis showed that while induction of POLG1 mutants still displayed delayed lagging-strand synthesis, Twinkle-induced stalling resulted in maturated, essentially fully double-stranded DNA intermediates. In the latter case, limited inhibition of POLG with dideoxycytidine restored the delay between leading- and lagging-strand synthesis. The observed cause-effect relationship suggests that Twinkle-induced stalling increases lagging-strand initiation events and/ or maturation mimicking conventional strand-coupled replication.

Original languageEnglish
Pages (from-to)3238-3251
Number of pages14
JournalNucleic acids research
Volume35
Issue number10
DOIs
Publication statusPublished - May 2007
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Genetics

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