Table S1.

Image processing statistics

Pixel size on the specimen, Å	1.2
Resolution at FRC = 0.143, Å	7
Total length of nonoverlapping segments, nm	29,290
No. of fibrils	29
No. of subunits (repeat units)	62,320
Segment size during refinement, nm	2.2–6.4*
Average twist per subunit, °	−0.769
Axial symmetry	Twofold
Average crossover distance, nm	110
Assumed repeat distance, Å	4.7
Fibril width, nm	10

*Bigger segments for straight fibrils and smaller segments for bent fibrils, as detailed in Rohou and Grigorieff (16).