Figure 4.

AtMAP65-1, not AtMAP65-6, promoted microtubule polymerization. A, Polymerization of tubulins under 0, 0.5, 1, 2, and 4 μm AtMAP65-1 fusion protein for 30 min. The degree of polymerization was monitored by the A₃₅₀ (y axis). B, Promotion of tubulin polymerization by AtMAP65-1 at different concentrations. Note that at the highest concentration (4 μm), approximately 35% more tubulins were present in the pellet than when there was no AtMAP65-1. C, AtMAP65-1 reduced lag time for tubulin polymerization. In the absence of AtMAP65-1, the lag time was about 3 min. In the presence of 1 or 0.5 μm AtMAP65-1, the lag time was estimated at about 40 or 60 s, respectively (see the arrows). D, Polymerization of tubulins in the presence of 0, 0.2, 0.5, 1, and 2 μm AtMAP65-6. Note there was no significant difference among them. E, The Cc for tubulin polymerization was lowered in the presence of AtMAP65-1. The Cc values of tubulin assembly were estimated at about 11 μm for polymerization of tubulins (line 2) and decreased to 5 μm when 1 μm of AtMAP65-1 was present (line 1).