Figure 2. Schematic illustrating interbase center distance (d_cc) parameters.

Interbase distance between adjacent base centers (labelled 1 and 2) is calculated for each base step (d_cc; dotted line). Calculated base centers are represented by green circles. For pyrimidines, the base center coordinates are equivalent to the ring centroid. For purines, the base center coordinates are the average of the imidazole and pyrimidine ring centroid coordinates.