Figure 3.

Conformation and hydration of the AP residues U16 (Left) and U6 (Right). Views of base pair step A5pU6-A15pU16 (A) along the helix axis (upper and lower base pair in cyan and yellow, respectively, and selected torsion angles in degrees), and (B) roughly perpendicular to the helix axis, into the minor groove (with hb distances in Å). Atoms are colored green, red, blue, and magenta for carbon, oxygen, nitrogen, and phosphorus, respectively. Atoms of a backbone portion from a neighboring duplex contacting the modified step in the minor groove are colored gray and red for carbon and oxygen, respectively. Hydrogen bonds are thin solid lines and water molecules are cyan spheres.