Elucidating the dynamic properties of cis-syn thymine dimer lesion-containing DNA using thermodynamic techniques



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Key to our understanding of skin cancer biology is quantitative information regarding the effects of ionizing radiation and the subsequent formation of base pair lesions on DNA. The cis-syn thymine dimer lesion results when ionizing radiation promotes a concerted [2+2] cycloaddition of two adjacent thymine bases in B-form DNA. The presence of these thymine dimers inhibits replication and transcription of the DNA. Here, we characterize the extent to which a single thymine dimer lesion distorts the structure of duplex DNA, as well as the extent to which a thymine dimer lesion distorts the dynamic structure of duplex DNA. Specifically, we ask how the thermodynamic and kinetic properties of duplex DNA are altered when the duplex structure contains a thymine dimer lesion. The work described within was designed to establish the thermodynamic effects of the thymine dimer lesion within various sequence contexts of DNA. We describe overall thermodynamic properties of several DNA duplexes, using UV visible spectrophotometry thermal melt experiments. To date, all thermodynamic studies on the thymine dimer lesion in DNA have shown that it is subtly destabilizing (small positive ΔΔG). Similar to observations made by other groups, we have seen that the thymine dimer lesion causes an enthalpic stabilization (-ΔΔH) and an entropic destabilization (+ΔΔS) in the DNA melting transitions. However, the major contributor to destabilization (as determined by greater percent change in ΔH or ΔS) is disputable. For one of our sequences, we show that entropic effects dominate the change in the equilibrium over the melting transition, while in a second sequence, enthalpic and entropic effects contribute equally to the change in the melting equilibrium. We propose that the thermodynamic destabilization by the thymine dimer lesion is complex and sequence-dependent.



Biochemistry, DNA damage, thymine dimer, DNA lesions, DNA repair