FAP81 is required for the stable assembly of the C1e-c subcomplex. (A–F) Comparison of tomographic slices (A and D) and isosurface renderings (B, C, E, and F) between the averaged CA repeats of WT (A–C) and fap81 (D–F), viewed in cross-sectional (A and D) and longitudinal (B, C, E, and F) orientations, shows that the C1e and C1c projections (orange/yellow brackets in A) are present in WT but missing in fap81 (white bracket in D). (G) Schematic drawing of the WT CA structure in longitudinal view to outline the densities of the C1a (red) and C1e (orange) projections and their interactions. Note the transition from 16-nm periodicity (C1a) to 32-nm periodicity (C1e). Blue dots indicate the locations of the FAP76 N-terminus. (H) An overlay of the averaged CA repeats of fap76-1 (transparent gray) and fap81 (colored) shows the interaction (cyan arrowheads) between a rod-shaped C1d density and the gray C1c density, which remains present in the fap76-1 CA and consists of at least the FAP81 protein. Scale bar in A, 20 nm (valid for A and D).