Electron density of the reconstructed PR772 virus normalized to the maximum value. (a) The outer structure of the PR772 virus at the isosurface value of 20% of the maximum electron density. (b) The inner 3D structure of the PR772 virus at the isosurface values of 85% (brown area), 75% (green area) and 20% (gray area). (c) A 3D section of the virus. (d) An electron-density slice of the virus. Amplitude values of less than 0.2 were set to gray color scale. The color map for (c) and (d) is the same. Images were up-sampled three times for better visibility. The scale bar in (d) is 30 nm.