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Nature. 2013 Oct 17;502(7471):393-6. doi: 10.1038/nature12585. Epub 2013 Sep 11.

Pif1 helicase and Polδ promote recombination-coupled DNA synthesis via bubble migration.

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1
Baylor College of Medicine, Department of Molecular & Human Genetics, One Baylor Plaza, Houston, Texas 77030, USA.

Abstract

During DNA repair by homologous recombination (HR), DNA synthesis copies information from a template DNA molecule. Multiple DNA polymerases have been implicated in repair-specific DNA synthesis, but it has remained unclear whether a DNA helicase is involved in this reaction. A good candidate DNA helicase is Pif1, an evolutionarily conserved helicase in Saccharomyces cerevisiae important for break-induced replication (BIR) as well as HR-dependent telomere maintenance in the absence of telomerase found in 10-15% of all cancers. Pif1 has a role in DNA synthesis across hard-to-replicate sites and in lagging-strand synthesis with polymerase δ (Polδ). Here we provide evidence that Pif1 stimulates DNA synthesis during BIR and crossover recombination. The initial steps of BIR occur normally in Pif1-deficient cells, but Polδ recruitment and DNA synthesis are decreased, resulting in premature resolution of DNA intermediates into half-crossovers. Purified Pif1 protein strongly stimulates Polδ-mediated DNA synthesis from a D-loop made by the Rad51 recombinase. Notably, Pif1 liberates the newly synthesized strand to prevent the accumulation of topological constraint and to facilitate extensive DNA synthesis via the establishment of a migrating D-loop structure. Our results uncover a novel function of Pif1 and provide insights into the mechanism of HR.

PMID:
24025768
PMCID:
PMC3915060
DOI:
10.1038/nature12585
[Indexed for MEDLINE]
Free PMC Article
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