Table 1.

Summary of line width values obtained for ¹³C,¹⁵N-labeled ligands in the presence of various RNA constructs

RNA	Secondary structure	Ligand (13C,15N-labeled)	Mg2+, mM	Characteristics	Δσ, Hz	Line width ligand, Hz
No RNA		Hypoxanthine			0.11	7.5 ± 1.0
GSRapt		Hypoxanthine		Specific hypoxanthine binding	0.13	31.5 ± 0.6
GSRapt		Hypoxanthine	5	Specific hypoxanthine binding	0.12	30.5 ± 0.4
ASRapt		Hypoxanthine		No binding of hypoxanthine	0.06	11.5 ± 0.5
Helix P2&P3 RNA		Hypoxanthine		No binding of hypoxanthine	0.20	9.6 ± 1.3
No RNA		Adenine			0.16	7.8 ± 0.1
ASRapt		Adenine	5	Specific adenine binding	0.04	27.8 ± 0.4
GSRapt		Adenine		No binding of adenine	0.03	12.1 ± 0.1
Helix P2&P3 RNA		Adenine		No binding of adenine	0.07	10.3 ± 0.6

The RNA constructs include the guanine riboswitch aptamer domain (GSR^apt), the adenine riboswitch aptamer domain (ASR^apt), and an RNA construct (helix P2&P3 RNA), which consists of the structural elements helices P2 and P3 and loops L2 and L3 but lacks the ligand binding site of the purine riboswitches (see SI Fig. 5 for details) (Δσ, deviation of individual DSS reference signal from mean DSS line width value; line width ligand, mean line width value of two signals H2 and H8 of the respective ligand).