Extended Data Fig. 4: Organization of the radial spoke head tetrameric core.

a, Topology diagram of the fold common to RSP9 and the middle domains of RSP4 and RSP6. The core of the fold is indicated with a grey background. Segments outside the core vary between the three proteins and are shown as they appear in RSP9. b, Three-dimensional structure of RSP9 colored according to the diagram in a. c, A helix-loop-helix motif found at the N-terminus of the RS head fold is used by all chains to dimerize with a neighboring subunit (RSP4 with RSP6 and RSP9 with itself, creating a homodimer). The RSP4-RSP6 dimer is shown as an example.