title: Mitotic chromosomes are constrained by topoisomerase II-sensitive DNA entanglements.
abstract: We have analyzed the topological organization of chromatin inside mitotic chromosomes. We show that mitotic chromatin is heavily self-entangled through experiments in which topoisomerase (topo) II is observed to reduce mitotic chromosome elastic stiffness. Single chromosomes were relaxed by 35% by exogenously added topo II in a manner that depends on hydrolysable adenosine triphosphate (ATP), whereas an inactive topo II cleavage mutant did not change chromosome stiffness. Moreover, experiments using type I topos produced much smaller relaxation effects than topo II, indicating that chromosome relaxation by topo II is caused by decatenation and/or unknotting of double-stranded DNA. In further experiments in which chromosomes are first exposed to protease to partially release protein constraints on chromatin, ATP alone relaxes mitotic chromosomes. The topo II-specific inhibitor ICRF-187 blocks this effect, indicating that it is caused by endogenous topo II bound to the chromosome. Our experiments show that DNA entanglements act in concert with protein-mediated compaction to fold chromatin into mitotic chromosomes.
authors.affiliation: Department of Physics, University of Illinois at Chicago, Chicago, IL 60607, USA.
authors.forename: Ryo
authors.initials: R
authors.lastname: Kawamura
authors.forename: Lisa H
authors.initials: LH
authors.lastname: Pope
authors.forename: Morten O
authors.initials: MO
authors.lastname: Christensen
authors.forename: Mingxuan
authors.initials: M
authors.lastname: Sun
authors.forename: Ksenia
authors.initials: K
authors.lastname: Terekhova
authors.forename: Fritz
authors.initials: F
authors.lastname: Boege
authors.forename: Christian
authors.initials: C
authors.lastname: Mielke
authors.forename: Anni H
authors.initials: AH
authors.lastname: Andersen
authors.forename: John F
authors.initials: JF
authors.lastname: Marko
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000951:Antigens, Neoplasm / Q000235:genetics / Q000378:metabolism*; D002875:Chromosomes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004247:DNA / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004250:DNA Topoisomerases, Type II / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008938:Mitosis / Q000502:physiology*; D009690:Nucleic Acid Conformation; D013314:Stress, Mechanical; D014357:Trypsin / Q000378:metabolism
chemical_list: D000951:Antigens, Neoplasm; D004268:DNA-Binding Proteins; D007527:Isoenzymes; D000255:Adenosine Triphosphate; D004247:DNA; D014357:Trypsin; D004250:DNA Topoisomerases, Type II