Table 1.

Diffraction data collection and refinement statistics

Data set	Native nicked bottom strand	Native nicked top strand	Anomalous Ca2+ nicked bottom strand	Anomalous Ca2+nicked top strand
Space group	P41212	P41212	P41212	P41212
Wavelength (Å)	0.979	1.03	2.29	2.29
Unit cell dimensions (Å)	a = b = 80.61 c = 127.09	a = b = 80.68 c = 128.32	a = b = 80.59 c = 127.93	a = b = 80.60 c = 128.68
Asymmetric unit content	1 complex	1 complex	1 complex	1 complex
D-min (Å)	2.1	2.3	2.7	2.9
Completeness (%)	99.7	99.7	100	100
R-syma (%, outer shell)	6.1 (51.6)	4.4 (43.4)	7.5 (43.0)	6.6 (38.7)
Redundancy (outer shell)	9.2 (9.2)	5.3 (5.1)	11.1 (10.8)	11.0 (9.8)
Refinement
Resolution (Å)	50–2.2	50–2.3
R-factorb (%)	26.8	25.5
R-freeb (%)	28.7	28.2
Number of atoms
Protein	1855	1855
Nucleic acid	978	978
Solvent	98	58
Metal ions	4	3
Rmsd bond lengths (Å)	0.008	0.007
Rmsd bond angles (°)	1.53	1.33
Ramachandran (%)
Allowed	98.5	99.5
Generously allowed	1.5	0.5

^aR_sym = Σ_hΣ_i|I_i(h) − 〈I(h)〉|/Σ_hΣ_iI(h).

^bR-factor = Σ(|F_obs| − k|F_cal|)/Σ|F_obs. R-free was calculated using a random 5% of the reflection data that was omitted in the refinement.