title: G-rich telomeric and ribosomal DNA sequences from the fission yeast genome form stable G-quadruplex DNA structures in vitro and are unwound by the Pfh1 DNA helicase.
abstract: Certain guanine-rich sequences have an inherent propensity to form G-quadruplex (G4) structures. G4 structures are e.g. involved in telomere protection and gene regulation. However, they also constitute obstacles during replication if they remain unresolved. To overcome these threats to genome integrity, organisms harbor specialized G4 unwinding helicases. In Schizosaccharomyces pombe, one such candidate helicase is Pfh1, an evolutionarily conserved Pif1 homolog. Here, we addressed whether putative G4 sequences in S. pombe can adopt G4 structures and, if so, whether Pfh1 can resolve them. We tested two G4 sequences, derived from S. pombe ribosomal and telomeric DNA regions, and demonstrated that they form inter- and intramolecular G4 structures, respectively. Also, Pfh1 was enriched in vivo at the ribosomal G4 DNA and telomeric sites. The nuclear isoform of Pfh1 (nPfh1) unwound both types of structure, and although the G4-stabilizing compound Phen-DC3 significantly enhanced their stability, nPfh1 still resolved them efficiently. However, stable G4 structures significantly inhibited adenosine triphosphate hydrolysis by nPfh1. Because ribosomal and telomeric DNA contain putative G4 regions conserved from yeasts to humans, our studies support the important role of G4 structure formation in these regions and provide further evidence for a conserved role for Pif1 helicases in resolving G4 structures.
authors.affiliation: Department of Medical Biochemistry and Biophysics, Umeå University, SE-901 87, Umeå, Sweden.
authors.forename: Marcus
authors.initials: M
authors.lastname: Wallgren
authors.affiliation: Department of Medical Biochemistry and Biophysics, Umeå University, SE-901 87, Umeå, Sweden.
authors.forename: Jani B
authors.initials: JB
authors.lastname: Mohammad
authors.affiliation: Department of Medical Biochemistry and Biophysics, Umeå University, SE-901 87, Umeå, Sweden.
authors.forename: Kok-Phen
authors.initials: KP
authors.lastname: Yan
authors.affiliation: Department of Medical Biochemistry and Biophysics, Umeå University, SE-901 87, Umeå, Sweden.
authors.forename: Parham
authors.initials: P
authors.lastname: Pourbozorgi-Langroudi
authors.affiliation: Department of Medical Biochemistry and Biophysics, Umeå University, SE-901 87, Umeå, Sweden.
authors.forename: Mahsa
authors.initials: M
authors.lastname: Ebrahimi
authors.affiliation: Department of Medical Biochemistry and Biophysics, Umeå University, SE-901 87, Umeå, Sweden nasim.sabouri@umu.se.
authors.forename: Nasim
authors.initials: N
authors.lastname: Sabouri
mesh_terms: D004247:DNA / Q000737:chemistry / Q000235:genetics; D004265:DNA Helicases / Q000235:genetics*; D004261:DNA Replication / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics*; D054856:G-Quadruplexes; D015966:Gene Expression Regulation, Fungal; D006147:Guanine / Q000378:metabolism; D006801:Humans; D009690:Nucleic Acid Conformation; D012568:Schizosaccharomyces / Q000235:genetics; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics*; D016615:Telomere / Q000235:genetics*
chemical_list: D004275:DNA, Ribosomal; D029702:Schizosaccharomyces pombe Proteins; D006147:Guanine; D004247:DNA; D004265:DNA Helicases; C468287:Pfh1 protein, S pombe