Structure of radial spokes (RS). (A) Various views of RS (blue) to highlight pseudo twofold symmetry of RS1 and RS2. Red: ODA. Cyan: IDA. Green: DRC. Yellow: IC/LC. Grey: MTD. In the left two panels, the proximal end is left. (B) Juxtaposed flagella structures of the wild-type and mutant Chlamydomonas lacking RSPs and the diagram of RSPs based on the structural and biochemical analyses. Modified from . (C) RS from Chlamydomonas and Tetrahymena , highlighting the difference between RS1/2 and RS3 as well as the similarity between the Tetrahymena RS3 and the short protrusion of Chlamydomonas flagella (arrows).