Image processing: subtomogram averaging. (a) Isolated C. reinhardtii axoneme. Top row: surface renderings of the density map obtained by averaging radial spokes (RS). Middle row: tomographic slices of the above density map. Bottom: surface renderings of the overall 3D structure: microtubule doublet (gray), outer dynein arms (turquoise), inner dynein arms (IDA, blue), the intermediate and light chains of IDAs (yellow), the dynein regulatory complex (green), and the radial spokes (red). RS1, radial spoke 1; RS2, radial spoke 2. Image copyright Pigino et al. (2011). (b) Flagellar motor of intact Borrelia. Left: tomographic slices of the averaged density map. Right: 3D isosurface views of the motor. Bars, 25 nm. Reproduced from Liu et al. (2009) with permission from the American Society for Microbiology. (c) Bacterial chemosensory receptors. Left: superposition of one ring of the crystal structure (P5 blue, CheW green) with its six receptor dimers (TM14, yellow) on the EM map (blue mesh) with its previously fit 18 receptor dimers (pink). Right: the arrangement of the receptor array produces P6 point symmetry (red; the asymmetric unit yellow). Image copyright Briegel et al. (2012).