FIGURE 1.

GDP-tub incorporation in spontaneous nucleated microtubules. A–D, GTP-tub (75 μm) was assembled in the absence (A) or in the presence of GDP-tub (37.5 μm (B), 75 μm (C), or 120 μm (D)). Either GTP-tub or GDP-tub was ³H-labeled, and ³H incorporation in microtubules was determined to measure GTP-tub (■) or GDP-tub (▩) incorporation. Total polymeric tubulin (□) was calculated by the summation of the GDP-tub and GTP-tub curves. E, plot of (polymeric GDP-tub concentration/polymeric GTP-tub concentration) ratios at maximum assembly time (max assem. time) versus (initial GDP-tub concentration/initial GTP-tub concentration) ratio. F, microtubule half-disassembly times t½ versus (initial GDP-tub concentration/initial GTP-tub concentration) ratio. t½ values were determined from the plots shown in panels A–D.