Resolution improvement of electron micrographs by the direct method for biotin-binding protein streptavidin

Direct-method phase extension has been applied to two-dimensional electrondiffraction data of the protein streptavidin. Structure-factor amplitudesfrom electron diffraction were combined with phases from the correspondingelectron micrographs. Maximum-entropy discrimination and cluster analysiswere used to derive a solution from a large number of random trials. The phase extension from 0.3 to 0.25nm led to substantial improvement of thereconstructed projection image quality.