Nucleic Acids Research Advance Access originally published online on August 28, 2009
Nucleic Acids Research 2009 37(19):6625-6634; doi:10.1093/nar/gkp701
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Nucleic Acids Research, 2009, Vol. 37, No. 19 6625-6634
© The Author(s) 2009. Published by Oxford University Press.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.5/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Structural Biology |
Arrangements of human telomere DNA quadruplex in physiologically relevant K+ solutions
iuk
koláková
ová
ková**To whom correspondence should be addressed. Tel: 420 541517188; Fax: 420 541211293; Email: mifi{at}ibp.cz
Received June 5, 2009. Revised July 27, 2009. Accepted August 9, 2009.
The arrangement of the human telomeric quadruplex in physiologically relevant conditions has not yet been unambiguously determined. Our spectroscopic results suggest that the core quadruplex sequence G3(TTAG3)3 forms an antiparallel quadruplex of the same basket type in solution containing either K+ or Na+ ions. Analogous sequences extended by flanking nucleotides form a mixture of the antiparallel and hybrid (3 + 1) quadruplexes in K+-containing solutions. We, however, show that long telomeric DNA behaves in the same way as the basic G3(TTAG3)3 motif. Both G3(TTAG3)3 and long telomeric DNA are also able to adopt the (3 + 1) quadruplex structure: Molecular crowding conditions, simulated here by ethanol, induced a slow transition of the K+-stabilized quadruplex into the hybrid quadruplex structure and then into a parallel quadruplex arrangement at increased temperatures. Most importantly, we demonstrate that the same transitions can be induced even in aqueous, K+-containing solution by increasing the DNA concentration. This is why distinct quadruplex structures were detected for AG3(TTAG3)3 by X-ray, nuclear magnetic resonance and circular dichrosim spectroscopy: Depending on DNA concentration, the human telomeric DNA can adopt the antiparallel quadruplex, the (3 + 1) structure, or the parallel quadruplex in physiologically relevant concentrations of K+ ions.