J. Biol. Chem., Vol. 266, Issue 15, 9508-9514, 05, 1991
Aggregates of oligo(dG) bind and inhibit topoisomerase II activity and induce formation of large networks
IK Chung and MT Muller
Department of Molecular Genetics, Ohio State University, Columbus 43210- 1292.
DNA cleavage by eukaryotic type II DNA topoisomerase (EC 5.99.1.3) was
strongly inhibited by an oligonucleotide containing 10 dGua residues.
Catalytic activities of topoisomerase II, as measured by relaxation and
decatenation reactions, were also inhibited by oligo(dG)10. Inhibition was
specific to oligo(dG)10; other oligonucleotides, nucleotides, or
single-stranded DNAs tested did not influence the activity of topoisomerase
II. Oligo(dG)10 did not inhibit other activities such as restriction
enzymes. Although the enzyme neither binds nor cleaves oligo(dG)10,
inhibition can be explained by the finding that topoisomerase II binds
tightly with aggregated oligo(dG) structures (estimated to contain between
20 and 30 molecules of monomeric oligo(dG)10) that form spontaneously prior
to addition of enzyme. These aggregated oligo(dG)-topoisomerase complexes
are large networks that can be pelleted by a 20-min centrifugation step in
a Microfuge. Western blotting with a monoclonal antibody confirmed that
topoisomerase II is trapped in these pellets. The ability of the enzyme to
form large DNA- protein networks could be a biochemical mechanism by which
topoisomerase II might promote or participate in chromosome condensation in
vivo prior to mitosis.
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