Extended Data Table 1.

Data collection, processing and refinement statistics

	WT declination		WT declination + CPSF6-FG	T=1 G60A/G61P	T=1 M66A	T=1 G60A/G61P/M66A
EMDB	EMD-26715		EMD-28186	EMD-28054	EMD-28057	EMD-26718
PDB	7urn		8ejl	8eep	8eet	7urt
Data collection, processing and map calculation
Voltage (kV)	300		300	300	200	300
Electron exposure (e-/Å2)	50		54	50	48	50
Defocus range μm)	0.5 to 2.5		0.75 to 2.5	0.5 to 2.5	0.5 to 2.5	0.5 to 2.5
Pixel size (Å)	1.08		1.08	1.08	0.75	1.08
Symmetry imposed	C5		C5	I	I	I
Particles	525,219		166,463	494,057	116,627	509,666
Map Resolution (Å)	3.4		3.9	2.2	3.1	2.4
FSC threshold	0.143		0.143	0.143	0.143	0.143
Coordinate modeling and refinement
Initial model	Chain A (pentamer) PDB 4xfx	Chains L,M,N (half-hexamer) PDB 4xfx	PDB 7urn	PDB 7urt	PDB 7urt	PDB 4xfx
Model resolution (Å)	3.4	3.6	4.1	2.5	3.4	2.5
FSC threshold	0.5	0.5	0.5	0.5	0.5	0.5
Map sharpening B-factor (Å2)	146.9	146.9	159.3	97.0	144.4	109.7
Model composition
Non-hydrogen atoms	1,725	5,175	4,431	1,726	1,726	1,726
Protein residues	221	663	619	221	221	221
IP6	2	0	0	2	2	2
B-factors (Å2)	73.2	78.8	117.0	42.9	42.6
Root mean squared deviations
Bond lengths (Å)	0.006	0.004	0.005	0.002	0.004	0.004
Bond angles (°)	0.623	0.508	0.545	0.647	1.019	0.554
Validation
Molprobity score	1.57	1.42	1.81	1.33	1.37	1.34
Clash score	8.40	5.79	7.23	3.95	6.23	4.05
Poor rotamers (%)	0.43	1.24	3.04	1.59	1.07	1.60
Ramachandran plot
Favored (%)	97.26	97.87	97.82	100	99.54	99.09
Outliers (%)	0	0	0	0	0	0
Z-score	1.00	1.79	1.74	1.98	1.87	1.22