Structures of averaged plus ends from yeast spindle MTs. (A) A slice from the single KMT (left) used as an alignment reference. No mask was used. Cell name and number of MTs averaged are shown in black. Slices are all at −43°. Strong development of image features is seen, including both a puck-shaped structure ∼55 nm from the MT tip and fibrils connecting this with flaring PFs. (B) Averages of KMTs from the S. cerevisiae cell named under each panel. Numbers of MTs are averaged at the top, the angle of the sampling slice is shown in white, and fibrils are indicated with arrowheads. Fibers associated with bending PFs are again visible, but not on an ipMT (B′). (C) Averages of KMTs from S. pombe. Fibers are again evident in averages (arrowheads), but they are oriented at diverse angles, perhaps because of the size of the fission yeast kinetochore. A mass of ill-defined shape ∼40 nm from the MT tip accompanies all KMTs (arrows) not ipMTs (C′). (D) PEET averages of particles from different regions of budding yeast nuclei. In each part of the figure, the left image is a slice cut through the average, where the right is a surface rendering. (D) Average of 100 particles far from the spindle, which we interpret as nucleosomes. (D′) Average of 64 particles near the plus ends of spindle MTs in a diploid prometaphase. These we interpret as kinetochores. (D″) Similar average of 58 particles from two haploid prometaphases. (D‴) Similar average from 68 particles from three haploid metaphases. Bars: (A–C) 50 nm; (D) 22 nm.