Electron micrographs (a–c, scale bars 50 nm) and 2D class averages (d–f, scale bars 10 nm) showing different tube-less, helical ESCRT-III filament bundles formed from Snf7, Vps24, and Vps2 upon detergent removal. The majority of ribbons adopted a zigzag shape (a, d), others appeared sinusoidal (b, e) and a third set consisted of helical ribbons with higher strand numbers (c, f). The ribbon dimensions are rounded averages, for details see Supplementary Table 1. g Unmasked 3D average of a, d shows that the center of the ribbon is a helical bicelle with its plane perpendicular to the tube axis (grey). There are two anti-parallel double-stranded filaments on both sides of the bicelle (red). h 3D average as in a, c with an asymmetric mask that included only one double-stranded filament (red). Inset: scale-matched densities corresponding to two closed-conformation IST1/CHMP8 subunits from EMD-64616 are shown for comparison. Source data are provided as a Source Data file.