Circular dichroism spectra of twelve short DNA restriction fragments of known sequence: a comparison of measured and calculated spectra.

The CD spectra of twelve DNA restriction fragments ranging in size from 12 to 360 base pairs are reported. Since the sequences of these fragments are known, it is possible to calculate their CD spectra from a set of nearest neighbor contributions derived from a combination of synthetic polydeoxyribonucleotides. While the calculations lead to good agreement in the negative band at approximately 245 nm, they generally reproduce the positive band at approximately 270 nm only poorly. The experimentally observed positive band consists of two peaks centered around 270 and 285 nm. The comparison of calculated and measured spectra reveals that end effects lead to increased disagreement for fragments smaller than approximately 40 base pairs. The disagreement between calculated and measured spectra can be partially attributed to the fraction of next nearest neighbors in the DNAs, which are also in the spectral components. Thus, the sequence specific CD contributions in the long wavelength region of the spectra extend at least to next nearest neighbor nucleotides and may extend beyond.