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Research the Literature on your OwnIf two microtubules are cross-bridged by Ase1, how can they be made to slide over one another by the action of kinesin-5? (Hints: When a protein is bound to one site on a microtubule wall, how hard is it to move that protein to an identical site just one or two tubulin subunits away? This kind of question can be answered by measuring the rate at which a microtubule-bound protein will diffuse on the microtubule surface. There may not yet be data for this question on Ase1, but other microtubule-binding proteins have been studied.)
What really happens when two oppositely directed motors are trying to push the same object in opposite directions? (Hint: look for relevant data on the motion of vesicles or microbeads coated with motor proteins).
What are the molecular mechanisms for the forces that push chromosome arms away from the poles of at least some vertebrate spindles? (Hint: check out both forces developed by MT polymerization and by the special class of kinesin-like proteins called “chromo-kinesins”.) What factors are likely to make one of these mechanisms more important than the other?
The older literature on mitosis includes descriptions of movements of many kinds of structures that associate with spindles: not just chromosome arms but also granules of various kinds. Find data on such movements from a variety of organisms, including higher plants, and see if you can formulate a single hypothesis about spindle action that accounts for all these motions. (Hint: the best data for answering this question come from studies on comparatively big cells, because their large spindles allowed accurate observations on such movements.)
Several lines of experimentation have led to our current view that spindle MTs are dynamic (polymerize and depolymerize rapidly), but not all the data say the same thing. Which spindle MTs are the most dynamic, the least dynamic, and which are in between? How where these MT identities and their rates of turnover established? How reliable are the data from each method? Working with the data you find the most convincing, do the relative labilities of different MT groups (kinetochore-associated vs not, interdigitating MTs, astral MTs) make sense in terms of building a successful mitotic apparatus?
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