Figure 3. Subtraction of unwanted densities in particle images.

Subtraction of densities corresponding to the bulk of the particle is shown in a schematic diagram illustrating a rotavirus triple-layered particle (in blue with external parts of the VP4 spikes in pink). (a) First, subunits of interest are removed from the reconstruction of the complex. A mask (green), defining the subunits of interest, is created and then applied on the particle reconstruction to remove densities within the mask. (b) The masked reconstruction is projected in the orientations of the particle images (top) to create a stack of masked particle projections (middle). These are then subtracted from the original particle images, to create a new stack of particle images (bottom) that contain density corresponding mainly to the subunits of interest.