J Biol Chem, Vol. 274, Issue 38, 27128-27138, September 17, 1999
Selective Nucleosome Disruption by Drugs That Bind in the Minor
Groove of DNA
Daniel J.
Fitzgerald and
John N.
Anderson
From the Department of Biological Sciences, Purdue University,
West Lafayette, Indiana 47907-1392
Previous studies have shown that drugs which bind
in the DNA minor groove reduce the curvature of bent DNA. In this
article, we examined the effects of these drugs on the nucleosome
assembly of DNA molecules that display different degrees of intrinsic
curvature. DAPI (4,6-diamidino-2-phenylindole) inhibited the assembly
of a histone octamer onto a 192-base pair circular DNA fragment from Caenorhabditis elegans and destabilized a nucleosome that
was previously assembled on this segment. The inhibitory effect was highly selective since it was not seen with nonbent molecules, bent
molecules with noncircular shapes, or total genomic DNA. This marked
template specificity was attributed to the binding of the ligand to
multiple oligo A-tracts distributed over the length of the fragment. A
likely mechanism for the effect is that the bound ligand prevents the
further compression of the DNA into the minor groove which is required
for assembly of DNA into nucleosomes. To further characterize the
effects of the drug on chromatin formation, a nucleosome was assembled
onto a 322-base pair DNA fragment that contained the circular element
and a flanking nonbent segment of DNA. The position of the nucleosome
along the fragment was then determined using a variety of nuclease
probes including exonuclease III, micrococcal nuclease, DNase I, and
restriction enzymes. The results of these studies revealed that the
nucleosome was preferentially positioned along the circular element in
the absence of DAPI but assembled onto the nonbent flanking sequence in
the presence of the drug. DAPI also induced the directional movement of
the nucleosome from the circular element onto the nonbent flanking
sequence when a nucleosome preassembled onto this template was exposed
to the drug under physiologically relevant conditions.
Copyright © 1999 by The American Society for Biochemistry and Molecular Biology, Inc.