Extended Data Figure 3. CryoEM maps and tilt-pair validation.

a, CryoEM density of the whole tri-snRNP at 5.9 Å resolution by “gold standard” Fourier Shell Correlation (FSC) of 0.143 criterion at two different contour levels. The high contour map (gold) shows well-resolved densities for protein and RNA helices and flat densities for beta-sheets. The low contour map (silver) shows densities for the more flexible head and arm. The map was sharpened by a B-factor of −214 Ų and low-pass filtered to 5.9 Å as determined by RELION. b, The unsharpened full map of tri-snRNP. c, The map resulting from multi-body refinement, in which tri-snRNP is divided into four parts: the head, body, arm and foot. This resulted in better density for the arm domain (indicated by red circles), which is at 20 Å resolution. d, Tilt-pair validation plot for tri-snRNP. This was obtained from 1196 particles from 32 micrograph pairs, imaged at 0° and 10° tilt angles. The position of each dot represents the direction and the amount of tilting for a particle pair in polar coordinates. Blue dots correspond to in-plane tilt transformations; red and purple dots correspond to out-of-plane tilt transformations. Blue dots cluster in the same region of the plot at a tilt angle of approximately 10° as indicated by the red circle.