Table 1:

Name and description of the systems used in this work.

Name of the system	Description	Starting structure example (only central base pairs shown, hydrogen atoms hidden for clarity, red is oxygen, blue is nitrogen, orange is phosphorous and grey is carbon atoms).
I-R	This model was constructed from idealized cylindrical coordinates based on X-ray fiber diffraction data(Arnott, Campbell, & Chandrasekaran, 1976). (rise = 3.38 Å, twist = 36.0°).
I-Rx	These coordinates are directly from the analysis of the 1.4 Å resolution single crystal X-ray diffraction data of the PDB entry code 355D(Shui, McFail-Isom, Hu, & Williams, 1998) (mean rise 3.29 Å, mean twist = 35.4°).
II-Ra	Theoretical cylindrical coordinate data of a DNA form having bases perpendicular to the helix axis was used to build this model (rise = 3.4 Å, twist = 34.6°).
II-Rb	The coordinates for this model are similar to the II-Ra coordinates above but with C2’-endo sugars, rather than C4’-exo (rise = 3.4 Å, twist = 34.6°).
II-L	This model was constructed from theoretical cylindrical coordinates of a DNA form having bases perpendicular to the helix axis(Alexander Rich & Zhang, 2003).
II-Lt	Coordinates for this model were built from theoretical cylindrical coordinates of a left-handed form of DNA designed to satisfy B-DNA fiber diffraction constraints(Gupta, Bansal, & Sasisekharan, 1980). Bases are tilted relative to the helix axis. (rise = 3.4 Å, twist = −36.0°).