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Figure 7.
Fig. 7. (a) Model of DNA-cleavage mechanism of HincII. M1 and
M2 mark the two metal ion binding sites. Dashes indicate direct
ligation to a metal ion or hydrogen bond from the 3′P to the
nucleophilic water, shown as a pink sphere marked nuc. The
scissile bond is colored red. (b) Cartoon of the connection
between the CSPS and the distance between the phosphorus of the
phosphate at the scissile phosphodiester bond (SP) and the
phosphate 3′ from the SP (3′P). Dashes indicate direct
ligation to the metal ion, M1, or hydrogen bond from the 3′P
to the nucleophile (water or hydroxide molecule) shown as a pink
sphere. Left: inactive conformation with the 3′P blocking the
nucleophile binding site on the M1 ion. Right: active
conformation where disruption of the CSPS separates SP from
3′P on each strand to allow the nucleophile to bind to the M1
ion. The scissile bond is shown in red.
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