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Figure 6.
Figure 6. Stereoviews showing the closing of the deep
groove in the vicinity of the bulges and three magnesium cations
with direct coordination to phosphates and N7 atoms (trigonal
form). (a) Axial coordination of Mg d by the phosphates of G9a
and G9b. Mg g and g' are each localized in a pocket formed by
the phosphate of A8 and the N7 of G9 of strands b and a,
respectively. The ribose of A8a adopts the C3' endo/O4' endo
conformation and its base is in the syn conformation, whereas
the ribose of A8b is shown here in one of the two conformations
(C2' endo). The line of sight is along the noncrystallographic
dyad axis. (b) Representative (2F[obs]-F[calc]) electron-density
map (light blue), superimposed with the (FMn[obs]-FMg[calc])
Fourier difference map (orange), contoured at 4s around site d
and at 6s around sites g and g' (see the Materials and methods
section).
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