The architecture of the IDAs on individual microtubule doublets. (a, d, and g) The surface rendering of doublets 2–8 (a), 9 (d), and 1 (g). (b, c, e, f, h, and i) Same section across the averaged density map and the schematic representation of doublets 2–8 (b and c), 9 (e and f), and 1 (h and i) showing the inner arm dynein pattern. Red arrows show the position of the absent dynein b/g adjacent to radial spoke S1, and green arrows show the bulb density on doublet 1. Red, IDA; light blue, ODA; blue, radial spokes; green, DRC; yellow, light chain (LC)/IC of dynein f. The heads of radial spokes were also seen (not depicted) but have been trimmed in these figures to show only the area around the doublets. (j) The doublet-numbering order was performed as described by Hoops and Witman (1983), with doublets 1, 5, and 6 having the beaklike projection and a 1-2 bridge between doublets 1 and 2. Double-ended black arrows indicate the beating plane. Bar, 20 nm.