A MODEL FOR CHROMOSOME MOVEMENT DURING MITOSIS

We present a new model for poleward chromosome movement during mitosis . The key points of the model are: (1) Kinetochore spindle fibres cont ain kinetochore microtubules linked to filaments; both the microtubule s and the filaments are attached to the kinetochore. (2) Motor molecul es which are fixed in a spindle matrix push poleward on the kinetochor e microtubules in anaphase, and push on the associated filaments as we ll. (3) In addition to the kinetochore fibre pulling the kinetochore p oleward, there are forces on the chromosomes themselves that push the chromosome arms poleward in anaphase; the forces on the chromosome arm s are independent of the forces on the kinetochore spindle fibres and also may arise from motor molecules in the spindle matrix. (4) Kinetoc hore microtubules add subunits at the kinetochore and lose subunits fr om both the pole and the kinetochore; both polymerization and depolyme rization are regulated by ''compression'' forces and by ''stretching'' forces on the microtubules themselves. Compression is caused by motor molecules pushing the kinetochore microtubules into the pole (during anaphase) or into the kinetochore (during prometaphase), and is caused by motor molecules pushing the chromosomes into the kinetochore fibre s; stretching is caused by motor molecules pulling kinetochore microtu bules out from the kinetochore. We view our model as a new way of look ing at mitotic processes, with most details yet to be worked out, rath er than as a detailed description of mitosis.