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M9471075.TXT
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1994-08-09
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Document 1075
DOCN M9471075
TI Alternative dna structures in topoisomerase II-DNA interactions.
DT 9409
AU Howard MT; Univ. of North Carolina at Chapel Hill
SO Diss Abstr Int [B]; 53(9):4481 1993. Unique Identifier : AIDSLINE
ICDB/94690788
AB The type II DNA topoisomerases are enzymes that can change the
topological state of DNA. This is accomplished by passing DNA strands
through each other via a transient break in the helix. The result of
this reaction is to relax or introduce DNA supercoils and to resolve
knotted or catenated DNAs. Topoisomerase activity is essential for many
aspects of DNA metabolism such as transcription which generates waves of
DNA supercoiling and replication that produces catenated daughter DNAs.
Several compounds that inhibit topoisomerase II are highly toxic to
actively replicating cells and have been used as anti-tumor agents.
These inhibitors act by trapping a topoisomerase II-DNA complex at the
cleavage step of the catalytic cycle. DNA cleavage can be captured by
exposing the complexes to a protein denaturants such as SDS. Analysis of
the cleavage products reveals that topoisomerase II acts at specific
locations on the DNA with some sequence preferences. In this study we
report that alternative DNA structures can affect topoisomerase II-DNA
interactions. A strong binding site for Drosophila topoisomerase II was
created by a sequence directed DNA bend. The shape of the bend brings
two distant DNA segments into close proximity creating a DNA crossover
or node. Because topoisomerase II binds two DNA segments simultaneously
it preferentially localizes to this structure. In the absence of a fixed
DNA crossover, topoisomerase II captures two DNA segments by random
collision. DNA gyrase, the type II topoisomerase from E coli, did not
recognize this structure although it did bind two DNA segments
simultaneously via a random collision event. We have identified a
cluster of strong topoisomerase II sites which map to a complex repeated
sequence element flanking the HIV isolate HXB2. This region is capable
of forming slipped pairing structures, cruciforms, or Z-DNA. We conclude
that topoisomerase II-DNA interactions can be affected by DNA structure
in addition to the primary sequence of DNA. (Full text available from
University Microfilms International, Ann Arbor, MI, as Order No.
AAD93-02534.)
DE Animal Binding Sites DNA/CHEMISTRY/*METABOLISM DNA Topoisomerase
(ATP-Hydrolysing)/*METABOLISM Drosophila Escherichia coli/ENZYMOLOGY
Nucleic Acid Conformation THESIS
SOURCE: National Library of Medicine. NOTICE: This material may be
protected by Copyright Law (Title 17, U.S.Code).