Functional metal ions in nucleic acids.

Metal ions are inevitably involved in almost every aspect of nucleic acid chemistry. Their most prominent role is certainly the maintenance of nucleic acid structural integrity. However, they serve various other roles as well, e.g. as catalytic co-factors in ribozymes, in determining the secondary structure of tetra-stranded helices, during RNA folding, and possibly even in enabling nucleobase-centred acid/base catalysis under physiological conditions and in modulating homogeneous genetic recombination. This tutorial review gives a compact overview of the multifaceted situations in which metal ions exert specific functions in nucleic acids, also including a discussion of structural metal ions in regular DNA and RNA as well as triple helices, guanine quadruplexes, and helical junctions. It has a strong focus on metal ions that are naturally present in living systems and only occasionally includes a description of the interaction of exogenous metal complexes with nucleic acids (or their components), provided that the results of these studies can be transferred into the context of endogenous metal ions.