| Abstract: | The circular dichroism spectra of many natural DNAs and double-stranded synthetic polynucleotides were obtained. The eight first-neighbor contributions to the CD spectra of a DNA have been extracted from these data. Therefore, the CD spectrum for any DNA with known first-neighbor frequencies may be easily calculated. For a natural DNA the CD spectrum may be approximated by assuming the first-neighbor frequencies have the most probable values consistent with the base composition. Under favorable conditions, the measured CD spectrum can be used to determine thirteen of the sixteen first-neighbor frequencies of a DNA to ± 0.02 mole percent. The TG, CA, and TA first-neighbor cannot be unambiguously resolved by our method. The accuracy of the first-neighbor frequency analysis depends on the number of different first-neighbors present in the DNA and the extent to which they differ from the most probable value. The extinction coefficient at 260 nm and the base composition can also be calculated from the CD spectrum. |
