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Figure 9.
Figure 9 A schematic diagram of the hydrogen-bonding networks
in the minor groove of the Z-DNA hexamer. (a) Hydrogen bonds
bridging N2 amino groups from guanine bases and phosphate groups
in the backbone. Arrows show the directions of the hydrogen
bonds (from proton donor to acceptor). Broken lines are
electrostatic interactions weaker than the hydrogen bond defined
in the text. A symmetry-related atom is marked #. (b) Hydrogen
bonds bridging O2 keto groups from cytosine bases. Wavy lines
represent the connection of the Z-DNA duplex. D[2]O124 has a
spherical contour in the neutron 2|F[o]| - |F[c]| Fourier map;
therefore, the interaction between this D[2]O molecule and Z-DNA
was ambiguously observed. Note that the hydrogen-bonding scheme
in the lower region differs from that in the upper region
because the D[2]O113, D[2]O137, D[2]O121 and D[2]O141 molecules
mimic the second spermine molecule in the Spr crystal
(containing two spermine molecules) as shown in Fig. 4-.
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