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J. Biol. Chem., Vol. 277, Issue 11, 9293-9301, March 15, 2002
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,
From the Department of Microbiology, Ohio State University,
Columbus, Ohio 43210
The roles and interdependence of DNA sequence and
archaeal histone fold structure in determining archaeal nucleosome
stability and positioning have been determined and quantitated.
The presence of four tandem copies of TTTAAAGCCG in the polylinker
region of pLITMUS28 resulted in a DNA molecule with increased affinity
(
G of ~700 cal mol
1) for the archaeal
histone HMfB relative to the polylinker sequence, and the
dominant, quantitative contribution of the helical repeats of the
dinucleotide TA to this increased affinity has been established. The
rotational and translational positioning of archaeal nucleosomes assembled on the (TTTAAAGCCG)4 sequence and on DNA
molecules selectively incorporated into archaeal nucleosomes by HMfB
have been determined. Alternating A/T- and G/C-rich regions were
located where the minor and major grooves, respectively, sequentially
faced the archaeal nucleosome core, and identical positioning results
were obtained using HMfA, a closely related archaeal histone also from
Methanothermus fervidus. However, HMfA did not have
similarly high affinities for the HMfB-selected DNA molecules, and
domain-swap experiments have shown that this difference in affinity is
determined by residue differences in the C-terminal region of
-helix
3 of the histone fold, a region that is not expected to directly
interact with DNA. Rather this region is thought to participate in
forming the histone dimer:dimer interface at the center of an archaeal
nucleosome histone tetramer core. If differences in this
interface do result in archaeal histone cores with different sequence
preferences, then the assembly of alternative archaeal nucleosome
tetramer cores could provide an unanticipated and novel structural
mechanism to regulate gene expression.
Present address: Alderon Biosciences, 120 Turner St., Beaufort, NC 28516.
§
To whom correspondence should be addressed: Dept. of Microbiology,
Ohio State University, Columbus, OH 43210. Fax: 1-614-292-8120; E-mail:
reeve.2@osu.edu.
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