Kinetochore Ultrastructure in Vincristine-treated Mammalian Cells

The ultrastructure of chromosomes from tissue culture cells blocked in division with vincristine sulphate or colchicine was examined. Kinetochores had a distinctive morphology consisting of trilaminar dense plates closely applied to the chromosomes. In longitudinal sections, kinetochores appeared as separate plates attached to opposite sides of the chromosomes. In transverse sections of some prometaphase chromosomes, however, the kinetochore resembled an incomplete ring-like structure encircling the chromatid pair. These observations indicate that sister kinetochores may be continuous during early stages of their formation.