Abstract
This chapter focuses on the interaction of metal ions mainly with RNA. It is an update of the previous Chapter 3.21 in the 2nd Edition of Comprehensive Inorganic Chemistry II (2013) but focusing solely on RNA. Metal ions are key to folding, structure, and function of any nucleic acid. These interactions are generally of a weak and highly dynamic nature as they concern mostly K+ and Mg2+ in living organisms. Aside from the large excess of loosely bound ions for charge compensation, a network of inner-sphere and outer-sphere interactions holds more specifically bound ions in place. Hence, metal ion binding to larger RNAs is rather complicated and has many facets. After a few general considerations on the basic properties of metal ions and the potential coordination sites on the RNA, the thermodynamics of metal ion binding to RNA and known metal ion binding motifs in RNA are described. This is followed by today's knowledge on the role of metal ions in folding, dynamics, sensing, and/or catalysis of riboswitches and ribozymes, respectively, is summarized.