Nucleic Acids Research Advance Access published online on December 22, 2008
Nucleic Acids Research, doi:10.1093/nar/gkn990
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Structural Biology |
A novel chair-type G-quadruplex formed by a Bombyx mori telomeric sequence
Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
*To whom correspondence should be addressed. Tel: +65 6514 1915; Fax: +65 6794 1325; Email: phantuan{at}ntu.edu.sg
Received September 2, 2008. Revised November 23, 2008. Accepted November 24, 2008.
Recently, the human telomeric d[TAGGG(TTAGGG)3] sequence has been shown to form in K+ solution an intramolecular (3+1) G-quadruplex structure, whose G-tetrad core contains three strands oriented in one direction and the fourth in the opposite direction. Here we present a study on the structure of the Bombyx mori telomeric d[TAGG(TTAGG)3] sequence, which differs from the human counterpart only by one G deletion in each repeat. We found that this sequence adopted multiple G-quadruplex structures in K+ solution. We have favored a major G-quadruplex form by a judicious U-for-T substitution in the sequence and determined the folding topology of this form. We showed by NMR that this was a new chair-type intramolecular G-quadruplex which involved a two-layer antiparallel G-tetrad core and three edgewise loops. Our result highlights the effect of G-tract length on the folding topology of G-quadruplexes, but also poses the question of whether a similar chair-type G-quadruplex fold exists in the human telomeric sequences.