Figure 1. Overall structure of the flagellar MS ring.

a, Schematic showing the location of the MS ring (blue) within the bacterial flagellum. b, Cartoon representation of the domain structure of FliF. c, Composite 3D cryo-EM reconstruction with different symmetries applied within masks (see methods). Regions occupied by RBM2 and RBM3 for each chain are similarly coloured in an alternating scheme, with the exception of chains for which only RBM3 can be seen (yellow). Regions assigned to 9 RBM1 domains are indicated in red as connectivity cannot be definitively assigned. d, Representative 2D class of cross-linked FliF complexes on graphene oxide surface. Scale bar, 100Å. e, Representative density for regions where de-novo building of protein domains was possible in (i, ii) the C33 averaged RBM3-region map and (iii) the C21 averaged RBM2_inner-region map. f, Final model for the 33mer FliF, coloured as in (b). g, Representative density for docking of the RBM2_outer and RBM1 domains.