Induction time-course of the estrogen-dependent transcriptional cascade and of the estradiol-triggered regulatory loop. A. 25 ml glucose selective medium were inoculated with W303-1A yeast cells, containing plasmids pVitBx2, pHCA/GAL4(1-93)ERVP16 and pGAL1-ER. A similar volume of galactose selective medium was inoculated with yeast cells containing plasmids pVitBx2 and pGAL1-ER. After adding 1 μM β-estradiol (solved in ethanol), or similar amounts of ethanol, samples were taken at the indicated time points and assayed for β-galactosidase (Miller units). A representative experiment is shown. B. 24 hours time-course of W303-1A yeast cells, containing the cascade system (plasmids pVitBx2, pHCA/GAL4(1-93)ERVP16 and pGAL1-ER) after adding 1 μM β-estradiol, compared with W303-1A yeast cells containing the loop system (plasmids p416GAL1-lacZ and p414GAL1-GAL4ERVP16) after adding two different hormone conentration (1 μM and 50 nM). The experiments were performed as in A. To facilitate comparison, the results were represented as the percentage of the maximal values reached by each culture, except for the loop 50 nM estradiol, wich was referred to the maximal value of the loop culture containing 1 μM estradiol. A representative experiment is shown.