Table S1.

Data collection and refinement statistics

Datasets	nsp14–nsp10	nsp14–nsp10–SAM	nsp14–nsp10–SAH–GpppA
Data collection statistics
Cell parameters
a, b, c, Å	189.9, 195.0, 179.8	189.0, 196.9, 180.1	187.0, 195.9, 181.0
α, β, γ, °	90, 90, 90	90, 90, 90	90, 90, 90
Space group	C2 2 21	C2 2 21	C2 2 21
Wavelength, Å	0.984	0.979	0.979
Resolution, Å*	50.0 (3.46) −3.4	50.0 (3.31) −3.2	50.0 (3.36) −3.30
No. of all reflections	346,535	747,221	339,184
No. of unique reflections	46,052	56,140	50,763
Completeness (%)	100.0 (100.0)	100.0 (100.0)	100.0 (100.0)
Average I/σ (I)	26.8 (2.3)	24.0 (2.44)	16.5 (1.4)
Rmerge† (%)	8.6 (91.7)	9.9 (93.0)	7.6 (87.7)
Refinement statistics
No. of reflections used [σ(F) > 0]	45,999	55,716	48,424
Rwork‡, %	21.8	24.3	21.7
Rfree‡, %	26.6	26.5	26.0
rmsd bond distance, Å	0.024	0.027	0.025
rmsd bond angle, °	1.343	1.179	1.445
Average B-value, Å	151.6	107.7	125.0
No. of protein atoms	10,172	10,172	10,172
No. of ligand atoms	0	52	152
No. of solvent atoms	0	0	0
Ramachandran plot
Residues in favored regions, %	96.02	97.35	95.63
Residues in allowed regions, %	3.67	2.50	4.21
Residues in disallowed regions, %	0.31	0.15	0.16

^*Numbers in parentheses are corresponding values for the highest-resolution shell.

^†R_merge = Σ_hΣ_l | I_ih-<I_h> |/Σ_hΣ_I <I_h>, where <I_h> is the mean of the observations I_ih of reflection h.

^‡R_work = Σ(||F_p(obs)|-|F_p(calc)||)/Σ|F_p(obs)|; R_free is an R factor for a selected subset (5%) of the reflections that was not included in prior refinement calculations.