Extended Data Fig. 5: Structure of the radial spoke head minimal complex (RSP4, 6, 9 and 10).

a, Coomassie-stained SDS-PAGE of the recombinant RS head minimal complex. Uncropped gel image is shown in Supplementary Fig. 1. b, Cryo-EM map (‘map 7’) of the RS head minimal complex colored according to its constituent chains. c, Model built de novo for the RS head minimal complex according to the map in b. d, The positions of the RS head minimal complex within the head region of a C. reinhardtii RS subtomogram- averaged map in grey mesh (EMD-1941)⁸ are shown. e, Cryo-EM data processing workflow for 3D classification, masking and refinement is shown. Examples of picked particles are indicated with green circles on the micrograph. Red boxes indicate the class that was chosen for the next step. The yellow box indicates the map used for model building and submitted to EMDB. See Methods for more details. f, Cryo-EM map colored by local resolution, estimated using RELION. g, Angular orientation distribution of all particles used in the final 3D reconstruction of the map. h, Fourier Shell Coefficient (FSC) curve measured by the Gold- standard method using RELION. i, Alignment of the RS head core from our two models (RS head minimal complex (RSP4, 6, 9 and 10) colored; RS head-neck complex (grey) with an r.m.s.d. of 0.6 Å, indicating the RS head tetrameric core is a rigid unit.