EXPLICIT CORRECTION OF SEVERELY NON-UNIFORM DISTRIBUTIONS OF CRYO-EM VIEWS

The quality of three-dimensional macromolecular image reconstructions by cryo electron microscopy strongly depends on the number and quality of respective two-dimensional projections and on their angular distribution in space. Distributions with one or a few strongly preferred particle orientations may result in maps deformed in certain directions. A simple removal of overrepresented views may improve the quality of the reconstructed maps when the level of noise in the two-dimensional projections is low and the dataset-size can afford this removal but is counterproductive or insufficient otherwise. Giving complementarily an increased weight to underrepresented views, or taking multiple copies of them during the reconstruction, may improve the results, naturally, depending on how much the views distribution is non-uniform. This work describes the results of three-dimensional reconstructions using an explicit correction of the number of over- and underrepresented projections for non-uniformly distributed sets. SynopsisAn explicit numerical leveling of non-uniformly distributed sets of 2D projections with the program VUE improves the 3D reconstructions and illustrate sources of image distortions.