Table 1.

Statistics of base stacking modes as observed in experimentally determined structures

Stacking Mode	Counta	X-ray				Countc	NMRb
		θtet (°)		dtet (Å)			θtet (°)		dtet (Å)
		Average	First SDd	Average	First SDd		Average	First SDd	Average	First SDd
Core
Partial 5/6-ring (Anti/Anti)	310	61.5	3.3	3.39	0.10	23	61.1	5.5	3.28	0.17
5-ring (Syn/Anti)	245	83.2	2.4	3.47	0.11	44	84.5	4.7	3.54	0.29
Partial 6-ring (Anti/Syn)	118	29.2	1.4	3.55	0.08	8	30.7	8.2	3.57	0.29
Interfacee
Partial 6-ring	4	26.2		3.50
6-ring	4	41.6		3.41
5/6-ring	3	56.5		3.41		15	61.8		3.43
5-ring	33	83.2	1.4	3.52	0.08	5	81.4		3.11

^aThe number of observed base stacking geometries that are defined uniquely within the unit cell or at the interface of symmetry mates.

^bA selection of NMR structures (Supplementary Table S4) were cataloged to determine if there exist fundamental differences between the base stacking modes exhibited in X-ray and NMR structures.

^cFor NMR structures, the base stacking geometry of a single count of stacked guanines is an average across all of the models present in a given PDB file.

^dStandard deviation (SD) values highlight the ensemble spread of our characterized geometries used to determine θ_tet and d_tet. They do not reflect the uncertainty in experimental measurements.

^e‘Partial 6-ring' stacking was observed for a mixed 5′-3′ stacked structure (PDB ID: 2AVJ) and ‘6-ring' stacking was observed for a 3′-3′ stacked structure (PDB ID: 2HRI) while ‘5/6-ring' and ‘5-ring' stacking were observed for 5′-5′ stacked G-quadruplexes. The interface geometries of some NMR structures (PDB ID: 1MY9 and 2RQJ) were observed to contain mixed base stacking modes at their stacking interface.