'Corkscrewing', as evidence for force generation within a detergent-extracted microtubule translocation system from insect ovaries.

Microtubule-based translocation channels within the ovaries of the hemipteran insect Notonecta have been isolated by microdissection, and then detergent-extracted to leave a bundle of some 30,000 aligned microtubules. On addition of ATP and other hydrolysable nucleotides the microtubule bundle contorts into a helical configuration, a property we have called 'corkscrewing', before straightening again. This we believe to be indicative of force generation within the bundle. Electrophoretic analysis of the bundle of native microtubules reveals many polypeptides apart from the tubulins, and a number of these comigrate with microtubule-associated proteins (MAPs), which copolymerize with tubulins in reassembled microtubules from the same system. Corkscrewing does not occur if the microtubule bundle is pretreated with salt, a procedure that removes MAPs from microtubules, suggesting that the force is generated by a MAP or MAPs. In addition, certain minor polypeptides comprising the native microtubules are ATP-sensitive, a property expected of a microtubule motor.