Metal ions are necessary for folding and function of catalytic RNA molecules. However, the structural and mechanistic roles of these ions are poorly understood. What little is known concerning their coordination properties and roles of action is mainly based on either crystal structures or on experiments with mononucleotides. This project focuses on the determination and thermodynamic characterization of metal ion binding motifs in large RNAs. We thereby apply mainly NMR spectroscopic methods to determine the structure of RNA molecules, but are also trying to obtain high resolution crystal structures of our constructs in combination with metal ions. Based on the such obtained structure, metal ion binding properties are then investigated in detail by variety of techniques like NMR, potentiometric pH titrations, hydrolytic cleavage experiments, fluorescence and others. At the center of our interest with regard to this project are naturally occurring self-splicing group II intron ribozymes, a family of large catalytic RNAs. As for all ribozymes, metal ions are essential for folding and catalysis of these large molecular machines with a size of up to several thousand nucleotides. Although only composed of four different nucleotides, group II introns and RNA in general thereby show a remarkable selectivity and specificity for certain kinds of metal ions. Our results contribute not only to the understanding of the global structure and function of these naturally occurring catalytic RNAs, but also promise to have a significant impact on Bioinorganic Chemistry and on RNA Biochemistry in general.