Dam1C/DASH oligomerizes into partial and complete rings in vitro. (A) Cryotomographic slice (60 nm) of MTs, encircled by Dam1C/DASH rings. The amorphous densities below and to the left of the white box are protein aggregates. (B) A series of cryotomographic slices (5 nm) through the position boxed in white in A, enlarged twofold. Magenta arrowhead: MT protofilament; green arrows: Dam1C/DASH decamers. (C) Cryotomographic slices (4.6 nm) showing front views of partial (left) and complete (right) Dam1C/DASH rings assembled around MTs. The bottom row shows the same rings but rotated 90° around the horizontal axis. Green arrowheads: densities of adjacent Dam1C/DASH oligomers; green boxes: approximate planes of the partial or complete ring taken in the top panels. (D) 3D models of Dam1C/DASH and MT complexes corresponding to top and bottom rows in C. (E) Two examples of Dam1C/DASH rings with bridges (green arrows), in the front (left) and side (right) views. (F) Asymmetric 3D class averages of Dam1C/DASH rings around MTs. Repeat subunits are numbered for class 1. Classes 2 and 3 (not shown) are very similar to class 4 and were included in the 49%. The top row is the front view. The middle and bottom rows are sequentially rotated 45° around the horizontal axis. Green arrowheads: protrusions; blue arrow: position in class average 4 that deviates from 17-fold symmetry. All density maps were masked to exclude the MT and contoured at 0.1 SD above the mean. (G) Enlarged, cutaway view of a 17-fold symmetrized Dam1C/DASH ring, with landmark motifs labeled. Note that the bridges appear shorter than in the individual subtomograms because their structures are extremely heterogeneous.