title: G-quadruplexes significantly stimulate Pif1 helicase-catalyzed duplex DNA unwinding.
abstract: The evolutionarily conserved G-quadruplexes (G4s) are faithfully inherited and serve a variety of cellular functions such as telomere maintenance, gene regulation, DNA replication initiation, and epigenetic regulation. Different from the Watson-Crick base-pairing found in duplex DNA, G4s are formed via Hoogsteen base pairing and are very stable and compact DNA structures. Failure of untangling them in the cell impedes DNA-based transactions and leads to genome instability. Cells have evolved highly specific helicases to resolve G4 structures. We used a recombinant nuclear form of Saccharomyces cerevisiae Pif1 to characterize Pif1-mediated DNA unwinding with a substrate mimicking an ongoing lagging strand synthesis stalled by G4s, which resembles a replication origin and a G4-structured flap in Okazaki fragment maturation. We find that the presence of G4 may greatly stimulate the Pif1 helicase to unwind duplex DNA. Further studies reveal that this stimulation results from G4-enhanced Pif1 dimerization, which is required for duplex DNA unwinding. This finding provides new insights into the properties and functions of G4s. We discuss the observed activation phenomenon in relation to the possible regulatory role of G4s in the rapid rescue of the stalled lagging strand synthesis by helping the replicator recognize and activate the replication origin as well as by quickly removing the G4-structured flap during Okazaki fragment maturation.
authors: From the College of Life Sciences, Northwest A & F University, Yangling, Shaanxi 712100, China.
authors: Xiao-Lei
authors: XL
authors: Duan
authors: From the College of Life Sciences, Northwest A & F University, Yangling, Shaanxi 712100, China.
authors: Na-Nv
authors: NN
authors: Liu
authors: From the College of Life Sciences, Northwest A & F University, Yangling, Shaanxi 712100, China.
authors: Yan-Tao
authors: YT
authors: Yang
authors: From the College of Life Sciences, Northwest A & F University, Yangling, Shaanxi 712100, China.
authors: Hai-Hong
authors: HH
authors: Li
authors: the CAS Key Laboratory of Soft Matter Physics, International Associated Laboratory of CNRS-Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China, and.
authors: Ming
authors: M
authors: Li
authors: the CAS Key Laboratory of Soft Matter Physics, International Associated Laboratory of CNRS-Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China, and sxdou@iphy.ac.cn.
authors: Shuo-Xing
authors: SX
authors: Dou
authors: From the College of Life Sciences, Northwest A & F University, Yangling, Shaanxi 712100, China, the Laboratoire de Biologie et Pharmacologie Appliquée, Ecole Normale Supérieure de Cachan, CNRS, 61 Avenue du Président Wilson, 94235 Cachan, France xxi01@ens-cachan.fr.
authors: Xu-Guang
authors: XG
authors: Xi
mesh_terms: D001483:Base Sequence; D055162:Biocatalysis; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D004265:DNA Helicases / Q000378:metabolism*; D054856:G-Quadruplexes; D007700:Kinetics; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D013050:Spectrometry, Fluorescence
chemical_list: D004247:DNA; D004265:DNA Helicases
keywords: DNA Helicase; DNA Replication; G-quadruplex; Genomic Instability; Kinetics; Replication Origin
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