BASE INCLINATIONS IN NATURAL AND SYNTHETIC DNAS

A sophisticated algorithm is developed to analyze flow linear dichroism data on nucleic acids for individual base inclinations. Measured absorption and linear dichroism data for synthetic AT and GC polymers and natural DNAs are analyzed. The reliability of the algorithm is tested on data for the synthetic polymers, and the results are similar to earlier, more straightforward analyses. For the first time, specific base inclinations are derived for all four bases individually from the linear dichroism data for natural deoxyribonucleic acids. For B-form DNA in aqueous solution at moderate salt the inclinations from perpendicular are as follows: d(A) = 16.1 +/- 0.5; d(T) = 25.0 +/- 0.9; d(G) = 18.0 +/- 0.6; d(C) = 25.1 +/- 0.8 deg. Our results indicate that the bases in synthetic and natural DNAs are not perpendicular to the helix axis, not even in the B form.