Figure 10.

The Mg²⁺-binding site which is closest to the cleavage site in the crystal structure. The blue sphere is a Mg²⁺ ion which is observed in the crystal structure (33). The distances between the Mg²⁺ ion and nearby base imino protons are shown. An arrow indicates the 5′-OH group of G2″, the leaving group of the cleavage reaction. The bases are colored according to the extent of the chemical shift change upon addition of 10 mM MgCl₂. Black, orange and red indicate <0.02, 0.06–0.09 and >0.10 p.p.m. chemical shift changes, respectively.