Nucleic Acids Research Advance Access originally published online on March 6, 2007
Nucleic Acids Research 2007 35(6):1978-1991; doi:10.1093/nar/gkm025
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Nucleic Acids Research, 2007, Vol. 35, No. 6 1978-1991
© 2007 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Structural Biology |
Biophysical studies of DNA modified with conformationally constrained nucleotides: comparison of 2'-exo (north) and 3'-exo (south) locked templates
1Laboratory of Medicinal Chemistry, Center for Cancer Research, National Cancer Institute at Frederick, Frederick, MD, 21702 USA, 2Molecular Targets Development Program and 3Laboratory of Proteomics and Analytical Technologies, SAIC-Frederick, Inc., Frederick, MD 21702 USA
*To whom correspondence should be addressed. Tel: +1 301 846 5905; Fax: +1 301 846 6033; Email: barchi{at}helix.nih.gov
Received November 16, 2006. Revised December 27, 2006. Accepted January 3, 2007.
The biophysical properties of oligodeoxyribonucleotides (ODNs) selectively modified with conformationally locked bicyclo[3.1.0]hexane pseudosugars (Maier,M.A., Choi,Y., Gaus,H., Barchi,J.J. Jr, Marquez,V.E., Manoharan,M. (2004) Synthesis and characterization of oligonucleotides containing conformationally constrained bicyclo[3.1.0]hexane pseudosugar analogs Nucleic Acids Res., 32, 3642–3650) have been studied by various techniques. Six separate synthetic ODNs based on the Dickerson Drew dodecamer sequence (CGCGAAT*T*CGCG) were examined where each one (or both) of the thymidines (T*) were substituted with a bicyclic pseudosugar locked in either a North (2'-exo) or South (3'-exo) ring pucker. Circular dichroism spectroscopy, differential scanning calorimetry and 1H NMR spectroscopy were used to examine the duplex stability and conformational properties of the ODNs. Replacement of one or both thymidines with North-locked sugars (RNA-like) into the dodecamer did not greatly affect duplex formation or melt temperatures but distinct differences in thermodynamic parameters were observed. In contrast, incorporation of South-locked sugar derivatives that were predicted to stabilize this standard B-DNA, had the unexpected effect of causing a conformational equilibrium between different duplex forms at specific strand and salt concentrations. Our data and those of others suggest that although DNA can tolerate modifications with RNA-like (North) nucleotides, a more complicated spectrum of changes emerges with modifications restricted to South (DNA-like) puckers.
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