Figure 6.

Kinetics of microtubule assembly. Microtubules were reconstituted in vitro with purified tubulin (1 mg/ml) and MAP2 (0.05 mg/ml) in buffer A. The increase of absorbance was monitored at 345 nm at 37°C and recorded every 30 sec for 15 min. Microtubule assembly was monitored either in the absence of steroid (●) or in the presence of 500 nM steroid [PREG (□), progesterone (×), or estradiol (▿)], or in the presence of both PREG and progesterone (○) or PREG and estradiol (▵), each at 500 nM.