Exploring purine N7 interactions via atomic mutagenesis: The group I ribozyme as a case study

Hydrogen bonds and stacking interactions involving the exogenous guanosine. (A) Schematic of hydrogen bonding interactions between the base of the exogenous guanosine (shown in blue) and the Tetrahymena group I ribozyme from functional (Michel et al. 1989; Forconi et al. 2009) and structural (Adams et al. 2004; Golden et al. 2005; Guo et al. 2005; Stahley and Strobel 2005) data. (B) The same interactions are present in the Azoarcus group I ribozyme structural model 3BO3. The nucleobase of residue G128 (light green), corresponding to residue C262 in the Tetrahymena intron, seems to stack with the exogenous guanosine (blue). The Mg²⁺ ion shown in Figure 2 is also shown in this figure.