Periodic DNA patrolling underlies diverse functions of Pif1 on R-loops and G-rich DNA.
Pif1 family helicases are conserved from bacteria to humans. Here, we report a novel DNA patrolling activity which may underlie Pif1's diverse functions: a Pif1 monomer preferentially anchors itself to a 3'-tailed DNA junction and periodically reel in the 3' tail with a step size of one nucleotide, extruding a loop. This periodic patrolling activity is used to unfold an intramolecular G-quadruplex (G4) structure on every encounter, and is sufficient to unwind RNA-DNA heteroduplex but not duplex DNA. Instead of leaving after G4 unwinding, allowing it to refold, or going beyond to unwind duplex DNA, Pif1 repeatedly unwinds G4 DNA, keeping it unfolded. Pif1-induced unfolding of G4 occurs in three discrete steps, one strand at a time, and is powerful enough to overcome G4-stabilizing drugs. The periodic patrolling activity may keep Pif1 at its site of in vivo action in displacing telomerase, resolving R-loops, and keeping G4 unfolded during replication, recombination and repair.DOI: http://dx.doi.org/10.7554/eLife.02190.001.
Center for the Physics of Living Cells, Department of Physics, University of Illinois at Urbana-Champaign, Urbana, United States.
Ruobo
R
Zhou
Center for the Physics of Living Cells, Department of Physics, University of Illinois at Urbana-Champaign, Urbana, United States Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, United States.
Jichuan
J
Zhang
Department of Molecular Biology, Princeton University, Princeton, United States.
Matthew L
ML
Bochman
Department of Molecular Biology, Princeton University, Princeton, United States.
Virginia A
VA
Zakian
Center for the Physics of Living Cells, Department of Physics, University of Illinois at Urbana-Champaign, Urbana, United States Howard Hughes Medical Institute, University of Illinois at Urbana-Champaign, Urbana, United States tjha@illinois.edu.
Taekjip
T
Ha
D004265:DNA Helicases / Q000737:chemistry / Q000502:physiology*; D004271:DNA, Fungal / Q000737:chemistry / Q000502:physiology*; D054856:G-Quadruplexes; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000502:physiology*
D004271:DNA, Fungal; D029701:Saccharomyces cerevisiae Proteins; C085463:PIF1 protein, S cerevisiae; D004265:DNA Helicases
G-quadruplexes; Pif1 family helicases; R-loops; single molecule analysis