Figure 4

Hormone-dependence and switch-off time course of the β-estradiol-triggered self-induced regulatory loop. 5 ml glucose cultures of W303-1A cells containing plasmids p416GAL1-lacZ and p414GAL1-GAL4ERVP16 were inoculated as in Fig 1 and grown for 14 hours in the presence of the indicated concentration of β-estradiol and assayed for β-galactosidase. The average and standard deviation of three different experiments is represented. B. 100 ml glucose medium were inoculated with yeast cells containing plasmids p416GAL1-lacZ and p414GAL1-GAL4ERVP16 and grown until stationary phase (19 h) in the presence of 50 nM estradiol. Cells were then washed three times by centrifugation and used to inoculate a new 100 ml culture lacking β-estradiol, at a OD(600 nm) of 0.2. Seven hours later (arrow) cells were washed again and used to inoculate a new culture at a OD(600 nm) of 0.2. As a control, a 100 ml glucose culture was inoculated at a OD(600 nm) of 0.2, from a saturated preculture grown in galactose. Samples were taken at the indicated times and assayed for β-galactosidase activity. A representative experiment is shown