Figure legend

FIGURE 3 A nucleus in mitotic prophase, with chromosomes (ch) and kinetochores (k). The spb has a diameter of about 250 nm in the plane of section and it appears in three consecutive sections so that the diameter perpendicular to the plane of section is also about 250 nm. Its thickness is 110 nm and it appears to be composed of two disks stacked on top of each other (b). The dense particles have been replaced by a dense halo which surrounds the spb and from which microtubules extend. Fig. 3 a-d is taken from consecutive serial sections. (a) Bar is 500 nm. x 30,000. (b) to (d) Bar is 100 nm. x 90,000. Fig. 3a gives an overview over the NAB positioning in the cell.

Figure notes

Fig. 3b clearly shows that the core structure consists of three major layers. Today we prefer to call the NAB a centrosome, since it appears to serve all its functions and contains many conserved centrosomal components.