DNA G-quadruplexes in the human genome: detection, functions and therapeutic potential

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Abstract

DNA G-quadruplexes (G4s) are guanine-rich sequences that fold into four-stranded structures. Recent progress in the detection and mapping of genomic G4 structures has provided new insights into their functions in regulating transcription and genome stability, and has revealed their potential relevance for cancer therapy.

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DNA replication through G-quadruplex motifs is promoted by the Saccharomyces cerevisiae Pif1 DNA helicase.

Katrin Paeschke, John A Capra, Virginia Zakian (2011)

G-quadruplex (G4) DNA structures are extremely stable four-stranded secondary structures held together by noncanonical G-G base pairs. Genome-wide chromatin immunoprecipitation was used to determine the in vivo binding sites of the multifunctional Saccharomyces cerevisiae Pif1 DNA helicase, a potent unwinder of G4 structures in vitro. G4 motifs were a significant subset of the high-confidence Pif1-binding sites. Replication slowed in the vicinity of these motifs, and they were prone to breakage in Pif1-deficient cells, whereas non-G4 Pif1-binding sites did not show this behavior. Introducing many copies of G4 motifs caused slow growth in replication-stressed Pif1-deficient cells, which was relieved by spontaneous mutations that eliminated their ability to form G4 structures, bind Pif1, slow DNA replication, and stimulate DNA breakage. These data suggest that G4 structures form in vivo and that they are resolved by Pif1 to prevent replication fork stalling and DNA breakage. Copyright © 2011 Elsevier Inc. All rights reserved.

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Pif1 family helicases suppress genome instability at G-quadruplex motifs

Katrin Paeschke, Matthew Bochman, P. Daniela Garcia … (2013)

The Saccharomyces cerevisiae Pif1 helicase is the prototypical member of the Pif1 DNA helicase family, which is conserved from bacteria to humans. We show that exceptionally potent G-quadruplex unwinding is conserved amongst Pif1 helicases. Moreover, Pif1 helicases from organisms separated by >3 billion years of evolution suppressed DNA damage at G-quadruplex motifs in yeast. The G-quadruplex-induced damage generated in the absence of Pif1 helicases led to novel genetic and epigenetic changes. Further, when expressed in yeast, human Pif1 suppressed both G-quadruplex-associated DNA damage and telomere lengthening.

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Unraveling cell type-specific and reprogrammable human replication origin signatures associated with G-quadruplex consensus motifs.

Emilie Besnard, Amélie Babled, Laure Lapasset … (2012)

DNA replication is highly regulated, ensuring faithful inheritance of genetic information through each cell cycle. In metazoans, this process is initiated at many thousands of DNA replication origins whose cell type-specific distribution and usage are poorly understood. We exhaustively mapped the genome-wide location of replication origins in human cells using deep sequencing of short nascent strands and identified ten times more origin positions than we expected; most of these positions were conserved in four different human cell lines. Furthermore, we identified a consensus G-quadruplex-forming DNA motif that can predict the position of DNA replication origins in human cells, accounting for their distribution, usage efficiency and timing. Finally, we discovered a cell type-specific reprogrammable signature of cell identity that was revealed by specific efficiencies of conserved origin positions and not by the selection of cell type-specific subsets of origins.