Mitotic chromosomes are constrained by topoisomerase II-sensitive DNA entanglements.
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.
Kawamura
Ryo
R
Department of Physics, University of Illinois at Chicago, Chicago, IL 60607, USA.
Pope
Lisa H
LH
Christensen
Morten O
MO
Sun
Mingxuan
M
Terekhova
Ksenia
K
Boege
Fritz
F
Mielke
Christian
C
Andersen
Anni H
AH
Marko
John F
JF
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
D000951:Antigens, Neoplasm; D004268:DNA-Binding Proteins; D007527:Isoenzymes; D000255:Adenosine Triphosphate; D004247:DNA; D014357:Trypsin; D004250:DNA Topoisomerases, Type II