Table 1. Data collection, refinement parameters and model statistics.

Data collection
Particles used in final 3D refinement	175,374
Pixel size (Å)	0.525
Defocus (μm)	−0.5
Voltage (kV)	300
Electron dose (e−Å−2)	40
R.m.s. deviations
Bonds (Å)	0.01
Angles (°)	1.53
Validation
Clashcore, all atoms	3.53
Good outliers (%)	0.0
Ramachandran plot
Favoured (%)	95.23
Allowed (%)	4.77
Outliers (%)	0.0
Refinement of C2 symmetry map (175,374 particles)
Resolution (Å)	3.2
Map sharpening B-factor (Å2)	−176
Fourier shell correlation criterion	0.143
Refinement of asymmetric map (175,374 particles)
Resolution (Å)	3.4
Map sharpening B-factor (Å2)	−179
Fourier shell correlation criterion	0.143
Refinement of asymmetric map (76,150 particles)
Resolution (Å)	3.6
Map sharpening B-factor (Å2)	−157
Fourier shell correlation criterion	0.143