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 contain kinetochore microtubules linked to filaments; both the microtubules and the filaments are attached to the kinetochore. (2) Motor molecules which are fixed in a spindle matrix push poleward on the kinetochore microtubules in anaphase, and push on the associated filaments as well. (3) In addition to the kinetochore fibre pulling the kinetochore poleward, there are forces on the chromosomes themselves that push the chromosome arms poleward in anaphase; the forces on the chromosome arms are independent of the forces on the kinetochore spindle fibres and also may arise from motor molecules in the spindle matrix. (4) Kinetochore microtubules add subunits at the kinetochore and lose subunits from both the pole and the kinetochore; both polymerization and depolymerization 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 fibres; stretching is caused by motor molecules pulling kinetochore microtubules out from the kinetochore. We view our model as a new way of looking at mitotic processes, with most details yet to be worked out, rather than as a detailed description of mitosis.