Fig. 2

Assessment of the efficiency of particle orientation distributions in previously published data sets. Each row, from left to right, shows density map of specimen, orientation distribution of particles in the data set, corresponding point spread function and efficiency (N is the number of asymmetric units, R _FSC is the FSC resolution and E _od the efficiency). Scale bars are 100 Å. Incomplete orientation sampling causes distortion of the 3D density map, which can be described by the shape of the point spread function. The beta galactosidase and the 20S proteasome data sets have relatively uniform orientation distributions, which benefit from the symmetry of the particles, and correspondingly high efficiencies. Their PSFs are close to spherical, meaning that the resolution is isotropic. The two ribosome data sets, where the particles exhibit preferred orientations, have lower efficiencies and yield 3D reconstructions, which are smeared (severely, in the last case) in a particular direction, corresponding to the elongation of the point spread function in that direction. Arrows and stars indicate the direction of minimum resolution