Figure 5.

Electron micrographs showing the products of microtubule assembly with MAP1 and MAP2 and the effect of AD P-tau on the assembly. Microtubule assembly was carried out from rat brain tubulin by the addition of MAP1 (a), MAP2 (b), or MAP2 and AD P-tau (c and d, respectively) as in Fig. 4. Aliquots of the reaction mixture were negatively stained with phosphotungstic acid after 4 (c) or 30 (a, b, and d) min of incubation. Only an occasional microtubule was seen with tubulin alone (data not shown) and with AD P-tau after 30 min of incubation (d), and a large number of microtubules was observed in the assembly with MAP1 (a), MAP2 (b), and MAP2 with AD P-tau after 4 min of incubation (c). (Bars = 1 μm for a-c and 0.5 μm for d.)