Figure 3.

EPR spectroscopy of a Mn²⁺ binding site within the hammerhead ribozyme. (A) EPR spectra of a 50 µM solution of Mn²⁺ alone (solid line) and in the presence of 10 µM of an RNA-DNA hybrid hammerhead ribozyme (dotted line). The addition of nucleic acid causes the six-line EPR spectrum of Mn²⁺ to diminish. (B) Model of the A9/G10.1 Mn²⁺ binding site in the tertiary-stabilized hammerhead ribozyme, as determined through energy minimization of crystallographic and ESEEM data. The Mn²⁺ ion coordinates the pro-R_P nonbridging oxygen of A9, the N7 of G10.1, and four water molecules. [Taken from (43) and (46), with permission.]