Crystallization and characterization of the thallium form of the Oxytricha nova G-quadruplex

Michelle L. Gill¹, Scott A. Strobel¹^,2^,* and J. Patrick Loria²^,*

¹ Department of Molecular Biophysics and Biochemistry, Yale University New Haven, CT 06520, USA ² Department of Chemistry, Yale University New Haven, CT 06520, USA

^*To whom correspondence should be addressed. Tel: +1 203 436 4847; Fax: +1 203 432 6144; Email: patrick.loria{at}yale.edu

^*Correspondence may also be addressed to Scott A. Strobel. Tel: +1 203 432 9772; Fax: +1 203 432 5767; Email: scott.strobel{at}yale.edu

Received June 20, 2006. Revised August 4, 2006. Accepted August 4, 2006.

The crystal structure of the Tl⁺ form of the G-quadruplex formedfrom the Oxytricha nova telomere sequence, d(G₄T₄G₄), has beensolved to 1.55 Å. This G-quadruplex contains five Tl⁺ions, three of which are interspersed between adjacent G-quartetplanes and one in each of the two thymine loops. The structuredisplays a high degree of similarity to the K⁺ crystal structure[Haider et al. (2002), J. Mol. Biol., 320, 189–200], includingthe number and location of the monovalent cation binding sites.The highly isomorphic nature of the two structures, which containsuch a large number of monovalent binding sites (relative tonucleic acid content), verifies the ability of Tl⁺ to mimicK⁺ in nucleic acids. Information from this report confirms andextends the assignment of ²⁰⁵Tl resonances from a previous report[Gill et al. (2005), J. Am. Chem. Soc., 127, 16 723–16732] where ²⁰⁵Tl NMR was used to study monovalent cation bindingto this G-quadruplex. The assignment of these resonances providesevidence for the occurrence of conformational dynamics in thethymine loop region that is in slow exchange on the ²⁰⁵Tl timescale.

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Nucleic Acids Research

Structural Biology

Crystallization and characterization of the thallium form of the Oxytricha nova G-quadruplex