The influence of microtubule-associated proteins on the interaction of vincristine with microtubules and tubulin was examined. Microtubules containing associated proteins were prepared in vitro from tubulin preparations which contained the proteins or from pure 6S tubulin and isolated microtubule-associated proteins. The presence of the associated proteins caused microtubules to be converted to stable spiral structures upon reacting with vincristine. When the proteins were absent, spirals were not formed, and the microtubules were completely disassembled by vincristine. At 0°, 6S tubulin was converted to amorphous aggregates by vincristine, whereas if the associated proteins were present spirals were formed.
Supported by American Cancer Society Grant CH-98, Department of Health, Education and Welfare Research Grant NS 11360, and Department of Health, Education and Welfare Research Service Awards HD 07066 and HD 02528 from the National Institute of Child Health and Human Development to the Kansas Center for Mental Retardation and Human Development.