Extended Data Fig. 3: Various observations in micrographs.

a. At 120 min, micrographs of the PHF reactions showed FIAs (cartoon at bottom left). In some instances, many FIAs appeared to originate from a single point, reminiscent of nucleation and growth of a crystal from an impurity (left two micrographs). In other instances, longer isolated FIAs were observed. b. At 140 min in the PHF reactions, some FIAs remained but most filaments yielded images that did not allow 3D reconstruction. Insets show 2D class averages; circular pie charts show the distribution of unsolvable filaments (grey) versus structures solved (coloured). c. At 160 min in the CTE reactions, nine structures could be solved from three replicates. d. At 180 min in the CTE reactions, some filament types appear to be branching, with specific structures in 2D class averages (insets). e. At 180 min in the CTE reactions, some filaments consist of multiple filament types (purple or blue). f. At 360 min in the PHF reactions, some QHFs (yellow) appear to be branching into two separate PHFs (red). g. At 360 min in the PHF reactions, some QHFs appear to convert into PHFs. Scale bar of 50 nm applies to all micrographs.