Figure 2.

(a–e) Electron micrographs of β protein forming helical filaments on dsDNA. (a) Compressed helix with a pitch less than 115 Å. (b) Helix with a pitch ranging from 115 to 135 Å. (c) Extended helix with a pitch greater than 135 Å. (d) Rotary-shadowed filament, showing left-handed protein helix. (e) Uncoiling of the filaments (arrows). (Scale bar = 700 Å.) (f) Fourier transform (simulated fiber pattern) generated by averaging the intensities from transforms of 59 individual β-DNA filaments. Only the single layer line at 1/125 Å⁻¹ is seen. (g) Pitch distribution of the β-DNA filaments.