title: BLM helicase facilitates telomere replication during leading strand synthesis of telomeres.
abstract: Based on its in vitro unwinding activity on G-quadruplex (G4) DNA, the Bloom syndrome-associated helicase BLM is proposed to participate in telomere replication by aiding fork progression through G-rich telomeric DNA. Single molecule analysis of replicated DNA (SMARD) was used to determine the contribution of BLM helicase to telomere replication. In BLM-deficient cells, replication forks initiating from origins within the telomere, which copy the G-rich strand by leading strand synthesis, moved slower through the telomere compared with the adjacent subtelomere. Fork progression through the telomere was further slowed in the presence of a G4 stabilizer. Using a G4-specific antibody, we found that deficiency of BLM, or another G4-unwinding helicase, the Werner syndrome-associated helicase WRN, resulted in increased G4 structures in cells. Importantly, deficiency of either helicase led to greater increases in G4 DNA detected in the telomere compared with G4 seen genome-wide. Collectively, our findings are consistent with BLM helicase facilitating telomere replication by resolving G4 structures formed during copying of the G-rich strand by leading strand synthesis.
authors.affiliation: Department of Cell Biology, Albert Einstein College of Medicine, New York, NY 10461 drosopou@aecom.yu.edu schildkr@aecom.yu.edu.
authors.forename: William C
authors.initials: WC
authors.lastname: Drosopoulos
authors.affiliation: Department of Cell Biology, Albert Einstein College of Medicine, New York, NY 10461.
authors.forename: Settapong T
authors.initials: ST
authors.lastname: Kosiyatrakul
authors.affiliation: Department of Cell Biology, Albert Einstein College of Medicine, New York, NY 10461 drosopou@aecom.yu.edu schildkr@aecom.yu.edu.
authors.forename: Carl L
authors.initials: CL
authors.lastname: Schildkraut
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004261:DNA Replication; D054856:G-Quadruplexes; D020862:GC Rich Sequence; D055786:Gene Knockout Techniques; D007700:Kinetics; D018345:Mice, Knockout; D053484:RecQ Helicases / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D018741:Replication Origin; D016615:Telomere / Q000502:physiology*; D000071657:Werner Syndrome Helicase
chemical_list: C097151:Bloom syndrome protein; D053484:RecQ Helicases; D000071657:Werner Syndrome Helicase; C499253:Wrn protein, mouse