title: Top3α is required during the convergent migration step of double Holliday junction dissolution.
abstract: Although Blm and Top3α are known to form a minimal dissolvasome that can uniquely undo a double Holliday junction structure, the details of the mechanism remain unknown. It was originally suggested that Blm acts first to create a hemicatenane structure from branch migration of the junctions, followed by Top3α performing strand passage to decatenate the interlocking single strands. Recent evidence suggests that Top3α may also be important for assisting in the migration of the junctions. Using a mismatch-dHJ substrate (MM-DHJS) and eukaryotic Top1 (in place of Top3α), we show that the presence of a topoisomerase is required for Blm to substantially migrate a topologically constrained Holliday junction. When investigated by electron microscopy, these migrated structures did not resemble a hemicatenane. However, when Blm is together with Top3α, the dissolution reaction is processive with no pausing at a partially migrated structure. Potential mechanisms are discussed.
authors.affiliation: Department of Biochemistry, Duke University Medical Center, Durham, North Carolina, United States of America.
authors.forename: Stefanie Hartman
authors.initials: SH
authors.lastname: Chen
authors.affiliation: Department of Microbiology, University of California Davis, Davis, California, United States of America.
authors.forename: Jody L
authors.initials: JL
authors.lastname: Plank
authors.affiliation: Lineberger Cancer Center, University of North Carolina, Chapel Hill, North Carolina, United States of America.
authors.forename: Smaranda
authors.initials: S
authors.lastname: Willcox
authors.affiliation: Lineberger Cancer Center, University of North Carolina, Chapel Hill, North Carolina, United States of America.
authors.forename: Jack D
authors.initials: JD
authors.lastname: Griffith
authors.affiliation: Department of Biochemistry, Duke University Medical Center, Durham, North Carolina, United States of America ; Institute of Cellular and Organismic Biology, Academia Sinica, Taipei, Taiwan.
authors.forename: Tao-shih
authors.initials: TS
authors.lastname: Hsieh
mesh_terms: D000818:Animals; D004265:DNA Helicases / Q000378:metabolism; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D045566:DNA, Cruciform / Q000378:metabolism* / Q000648:ultrastructure; D004330:Drosophila; D029721:Drosophila Proteins / Q000378:metabolism; D011485:Protein Binding; D013379:Substrate Specificity
chemical_list: D045566:DNA, Cruciform; D029721:Drosophila Proteins; D004265:DNA Helicases; C470639:blm protein, Drosophila; D004264:DNA Topoisomerases, Type I