Conformational Preferences of DNA Strands from the Promoter Region of the c-MYC Oncogene

We characterized the conformational preferences of DNA in an equimolar mixture of complementary G-rich and C-rich strands from the promoter region of the c-MYC oncogene. Our CD-based approach presupposes that the CD spectrum of such a mixture is the spectral sum of the constituent duplex, G-quadruplex, i-motif, and coiled conformations. Spectra were acquired over a range of temperatures at different pH and concentrations of KCl. Each spectrum was unmixed in terms of the predetermined spectra of the constituent conformational states to obtain the corresponding weighting factors for their fractional contributions to the total population of DNA. The temperature-dependences of those contributions then were analyzed in concert according to a model based on a thermodynamic representation of the underlying equilibria. Fitted estimates of the melting enthalpy and temperature obtained for the duplex, G-quadruplex, and i-motif imply that the driving force behind dissociation of the duplex and the concomitant format...