The encoded protein can resolve gquadruplex structures and rnadna hybrids at the ends of chromosomes. Assembly of a gquadruplex repair complex by the fancj. Gquadruplex g4 structural motifs have been linked to transcription 1,2, replication 3 and genome instability 4,5 and are implicated in cancer and other diseases 6,7,8. The yeast pif1 helicase prevents genomic instability caused by g. The saccharomyces cerevisiae pif1 helicase is the prototypical member of the pif1 dna helicase family, which is conserved from bacteria to humans. Smallmolecule gquadruplex stabilizers reveal a novel pathway of. Pif1 dna helicase is a potent unwinder of gquadruplex g4 structures in vitro and functions to maintain genome stability at g4 sequences in saccharomyces cerevisiae. Human pif1 helicase is a gquadruplex dnabinding protein with gquadruplex dnaunwinding activity cyril m.
The dna helicase pif1 actively destabilizes ceb1 during vegetative growth. Pif1 is essential for efficient replisome progression. G4 dna is a noncanonical dna structure consisting of a stacked array of gquartets held together by base pairing between guanine bases. This gene encodes a dnadependent adenosine triphosphate atpmetabolizing enzyme that functions as a 5 to 3 dna helicase. Likewise, in yeast, the absence of a g4 unwinding helicase, pif1, induces.
The interplay between gquadruplex and transcription. Mms1 is a novel factor supporting pif1 helicase binding to g4s. Using a pulldownbased approach, we identified in yeast, among known g4. The yeast pif1 helicase prevents genomic instability. Interestingly, recently it has been described that gquadruplexstabilizing compounds, such as pyridostatin pyr or cx5461, are toxic to brca1. Here we show that exceptionally potent gquadruplex unwinding is conserved among pif1 helicases. Mms1 is an assistant for regulating gquadruplex dna. Human pif1 helicase is a gquadruplex dnabinding protein. The lack of in vivo redundancy between sgs1 and pif1 in this novel. Pif1 family helicases suppress genome instability at g.
Since then, the number of studies reporting gquadruplex dna unfolding by helicase enzymes has rapidly increased. Gquadruplex unwinding helicases and their function in. Overexpressing the g4dna helicase pif1 in neurons exposed to the g4 stabilizer improves phenotypes associated with g4dna stabilization. Complementary roles of pif1 helicase and single stranded dna. Using a pull downbased approach, we identified in yeast, among known g4. The yeast pif1 helicase prevents genomic instability caused by gquadruplexforming ceb1 sequences in vivo cyril ribeyre1. Recently, the increasing availability of genome sequences has revealed that pif1 helicases are also widely found in diverse prokaryotes, but it is currently unknown what physiological functions prokaryotic pif1 helicases might perform.
G4stabilising ligand o r when the helicase pif1 is disrupted 56. Stable telomeric gquadruplex structures were unfolded in a stepwise manner at a rate slower than that of duplex dna unwinding. Gquadruplex g4 structures can form in dna and rna molecules when. Strikingly, pif1 unfolds and then halts at the ssdsdna junction, followed by rapid reformation of g4 and acrobatic reinitiation of unfolding by the same monomer. Mms1 is an assistant for regulating gquadruplex dna structures. We show that pif1 is very efficient in vitro in processing gquadruplex. Human pif1 helicase is a gquadruplex dnabinding protein with gquadruplex dnaunwinding activity. Moreover, pif1 helicases from organisms separated by more than 3billion years of evolution. The unwinding process of a duplex motif immediately after a quadruplex structure by the action of the pif1 helicase has been recently investigated by. Pif1 proteins are helicases that in yeast are implicated in the. Quadruplex nucleic acids as novel therapeutic targets.
Structural basis for dna unwinding at forked dsdna by two. Moreover, pif1 helicases from organisms separated by 3 billion years of evolution suppressed dna damage at gquadruplex motifs in yeast. Pif1 family helicases, which are found in nearly all eukaryotes, have important roles in both nuclear and mitochondrial genome maintenance. The helicase pif1 facilitates resection over sequences prone to. In a single molecule fret assay they found that pif1 helicase was unable to resolve a duplex structure when preceded by a quadruplex motif. Thus, pif1 unfolds single g4 structures repetitively.
Pif1 helicase family members have been shown to efficiently unwind g4. Pif1 5to3 dna helicase is a protein that in humans is encoded by the pif1 gene. Fancj promotes dna synthesis through gquadruplex structures. The fancj helicase unfolds gquadruplexes g4s in human. We show that exceptionally potent gquadruplex unwinding is conserved amongst pif1 helicases.
In vitro and in vivo, the yeast pif1 helicase is able to unwind fourstranded gquadruplex g4 dna efficiently and suppress the genomic instability that occurs at such structures. Gquadruplexes and helicases nucleic acids research. Gquadruplexes and helicases oscar mendoza1,2, anne bourdoncle1,2. Finally, in performing these studies we discovered a novel and. Furthermore, it is found that pif1 unfolds g4 sequentially in two large steps. Both pif1 and pfh1 can unwind gquadruplex structures in vitro 1823. Gquadruplex structures mark human regulatory chromatin. The first indication of how gquadruplex structures could be unfolded enzymatically came in the late 1990s with reports that some wellknown duplex dna helicases resolved these structures in vitro. Here, we developed and utilized a livecell imaging approach to quantitatively measure the progression rates of single replication forks through different g4 containing sequences in individual yeast cells. Sanders1 institute for cancer studies, university of shef. Pif1 helicase unfolding of gquadruplex dna is highly dependent on.