The [Mg2+]-dependence of the Mg2+ and Na+ (or K+) binding fractions per nucleotide for six different test systems: 80-nt RNA duplex (A-form helix) with 10mM Na+ (A), 76-nt yeast tRNAPhe (PDB ID: 1TRA74) with 32 mM Na+ (B), 58-nt fragment of rRNA (PDB ID: 1HC875) with 20 (C) and 60 mM K+ (D), respectively, adenine riboswitch with 50 mM K+ (E), and rRNA-protein complex with 60 mM K+ (F), respectively. The experimental data in A, B, C and D, E, and F are from the References 95, 96, 97, 98, and 99, respectively.