Fig. 4.

Random conical tilt reconstruction of the S. pombe U5.U2/U6 complex in cryo-negative stain. (A) Six representative class averages of U5.U2/U6 particles selected from images of untilted specimens in cryo-negative stain (Upper) and the random conical tilt reconstructions calculated from the corresponding particles selected from the images of the tilted specimens (Lower). The number of particles in each projection average is shown in the lower right corner of each average. The last two classes result in 3D structures that are substantially smaller than the first four structures. Side length of individual panels is 54 nm. (Scale bar, 5 nm.) (B) 3D reconstruction of the S. pombe U5.U2/U6 complex filtered to 40-Å resolution combining particles from the first four classes in A and particles associated with additional class averages that clearly resemble these first four classes (see SI Fig. 7; merged classes are marked with a “+”). The complex is rotated about the vertical axis in 60° steps or about the horizontal axis by 90° or 180° steps (in reference to the top left structure), as indicated by arrows. (Scale bar, 5 nm.)