Figure 1.

Catalytic metal ions are bound within a sea of metal ions that coat RNA. A three-dimensional model for the Tetrahymena ribozyme complexed with the oligonucleotide substrate is depicted, with the oligonucleotide substrate (S) shown in green, the internal guide sequence (IGS) of the ribozyme in yellow, and the rest of the ribozyme in light gray. P1 is the duplex formed between S or P and the IGS. The blue dots depict the numerous metal ions that coat the RNA backbone; this ribozyme, which contains ∼400 nucleotides, is expected to bind 100–200 divalent metal ions (33, 68–70). The red dots depict specific active site metal ions that directly participate in the chemical reaction, which are the focus of this investigation. Adapted from an original drawing by L. Jaeger.