Nucleic Acids Research, Vol 24, Issue 9 1594-1601, Copyright © 1996 by Oxford University Press
ML Carpenter, G Lowe and PR Cook
During replication and recombination, two DNA duplexes lie side by side. We
have developed reagents that might be used to probe structure during these
critical processes; they contain two intercalating groups connected by a
rigid linker that forces those groups to point in opposite directions. If
their stereochemistry proves appropriate, such structure-specific agents
should intercalate specifically into adjacent duplexes in the Y- and
X-shaped structures (i.e. 3- and 4-way junctions, now known as 3H and 4H
junctions) found at replication and recombination sites. We prepared DNA
structures in which four duplexes were arranged in all possible
combinations around 2- and 4-way junctions and then probed the
accessibility to DNase I of all their phosphodiester bonds. In the absence
of any bis-intercalators, 7-9 nucleotides (nt) in each of the strands in
4-way junctions were protected from attack; protected regions were
significantly offset to the 3' side of the junction in continuous strands,
but only slightly offset, if at all, in exchanging strands. All the
intercalators decreased accessibility throughout the structure, but none
did so at specific points in the two adjacent arms of 4-way junctions.
However, one bis-intercalator--but not its sister with a shorter linker--
strikingly increased access to a particular CpT bond that lay 9 nt away
from the centre of some 4-way junctions without reducing access to
neighbouring bonds. Binding was both sequence and structure specific, and
depended on complementary stereochemistry between bis-intercalator and
junction.
ARTICLES
The structure of 4-way DNA junctions: specific binding of bis- intercalators with rigid linkers
The Sir William Dunn School of Pathology, University of Oxford, UK.
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