FAP216, a C1c protein that may bridge the C1 microtubule and peripheral C1c densities. (A–H) Comparisons of tomographic slices (A, B, E, and F) and isosurface renderings (C, D, G, and H) between averaged CA repeats of WT (A–D) and fap216 (E–H) viewed in cross-sectional (A, C, E, and G) and longitudinal (B, D, F, and H) orientations shows that the fap216 CA lacks a small C1c density (white arrowheads in E–H) that in WT connects between C1 microtubule protofilament 2 and peripheral C1c densities (yellow arrowheads in A–D). In addition, part of the C1e projection (orange arrowheads in A and C) that bridges between the C1e-c subcomplex and the C1a projection is reduced in fap216 (light orange arrowhead in E and G). Classification analysis confirmed that 57% of the fap216 CA repeats lack this C1e density (see Fig. S4). Scale bar in F, 20 nm (valid for all EM images).