Fig. 1. Mouse urothelial plaques. (A) Concave urothelial plaques make up almost the entire mouse urothelial apical surface (arrows) as well as large cytoplasmic fusiform vesicles (arrowheads). Scale bar: 100 nm. (B) A negatively stained, isolated mouse urothelial plaque showing a crystalline hexagonal array of 16 nm uroplakin particles. Scale bar: 100 nm. (C) The calculated diffraction pattern of a frozen-hydrated mouse urothelial plaque. Each spot with a signal/noise ratio of >1 is shown as a square; the size of the square is proportional to its signal/noise ratio. The number in each square is the `IQ' number of the diffraction spot [IQ of 1 to 7 correspond to signal-to-noise ratio of 7 to 1, respectively (Henderson et al., 1990)]. Circles are drawn at contrast transfer function (CTF) correction zeros; one spot at 6.9 Å (IQ=3) resolution is marked with an arrow.