Microtubule-associated-protein MAP1 is not implicated in the polymerization of microtubules.

Addition of DNA to microtubule protein solutions results in a decrease of the amount of the high-molecular-weight microtubule-associated proteins (MAP1 and MAP2) available for polymerization. Complete removal of MAP1 from microtubules requires lower concentrations of DNA compared to MAP2. Removal of MAP1 from microtubules has little or no effect on microtubule polymerization (nucleation and propagation). In contrast, removal of MAP2 produces a marked decrease in microtubule polymerization. Incubation of microtubular protein with DNA results in complete disappearance of the 30-S ring-shaped oligomers at concentrations of DNA which are not markedly inhibitory of polymerization.