Fine structure of the kinetochores in vinblastine sulfate-treated cells

Cells arrested in mitosis by vinblastine sulfate (Velban, Lilly) have prominent kinetochores or centromeres showing details of fine structure usually not seen in untreated dividing cells. In many of these cells 250-300 Å wide bands of electron-dense material surrounded by and separated from the chromatin by fine fibrous or amorphous, light-stained material are seen in the kinetochore region. In some sections these dense bands are as long as 4500, and often more than one band can be seen in the kinetochore region. In suitable sections, the median dense band is seen to consist of two apparent subunits which are 100 Å wide and separated by a 50-60 Å space.