DC analysis on wild type, oda4 (lacking ODA but retaining DC), oda1 (lacking both ODA and DC), and the doublet 1 average from wild type, oda11, oda4, and oda4s7. The yellow crosses show the center of the extra density and are at the same position in all cross sections. (a) Cross section of the common IDA architecture of wild type with the yellow line indicating the plane of the yz section. (b) yz section of wild type (wt) showing the 24-nm repeat. (c) yz section of oda4 also showing the 24-nm spacing (black arrowheads). (d) No 24-nm repeat is shown in oda1. (e) yz section of the doublet 1 average. (f) Horizontal section of a tomogram involving doublet 1 from wild-type flagellum. ODA is present but with no regular 24-nm periodicity. Red dotted lines indicate the regions with ODA. (g) Overlap of surface rendering of wild type, oda4, and the difference map between oda4 and oda1, showing that the 24-nm periodicity from the difference map (red) is at exactly the same place as the interface of ODA with the A-tubule. The surface rendering of wild type and oda4 are represented by mesh and gray surfaces, respectively. Bars, 20 nm.