We have probed the electrostatic environment of the active site of the Tetrahymena group I ribozyme (E) using protonated 2'-aminoguanosine (), in which the 2'-OH of the guanosine nucleophile (G) is replaced by an group. At low concentrations of divalent metal ion (2 mM Mg(2+)), binds at least 200-fold stronger than G or G(NH)()2, with a dissociation constant of </=1 microM from the ribozyme. ol...
