Book of Abstracts: Albany 2009

category image Albany 2009
Conversation 16
June 16-20 2009
© Adenine Press (2008)

A Low-Temperature Thermal Transition for Quadruplex DNAs

It is often assumed that the G-quartet structure that dominates near room temperature is the only low-temperature form of these DNAs. Here we present evidence for additional low-temperature structures of two G-quartet sequences that dominate below 12°C at moderate salt concentrations. Using analytical ultracentrifugation, we found that the sedimentation coefficients of G-quadruplex DNAs have minimum values near 12°C while that of a representative single-stranded DNA increases monotonically with temperature. The minimum in S20w observed with G-quadruplex indicates that at lower temperatures, G-quadruplexes are less compact than they are at ~12°C. Circular dichroism and fluorescence anisotropy data are also consistent with thermal transition near 12°C. We interpret this as evidence in the presence of a conformation that is more stable at low temperature than the dominant conformation that is observed at 20°C. In protein systems, cold denaturation is a characteristic of unfolding transitions with ΔCp>0; the contrasting behaviors of quadruplex and single-stranded DNAs suggests that the magnitude and possibly the sign of ΔCp may depend on the secondary structures of initial and final states.

This work was supported by the National Institutes of Health [GM070662].

Lance M. Hellman
Whitney Tackett
Emily Lawson
Michael G. Fried

Department of Molecular and
Cellular Biochemistry
Center for Structural Biology
University of Kentucky College of Medicine
Lexington, KY 40536