Hormone-dependent regulation of β-galactosidase by the different systems analysed in this work. β-galactosidase activities (Miller units) of W303-1A (A, B, C) or BY4741 (D) cells containing the following plasmids: (A) p416GAL1-lacZ and pHCA/GAL4(1-93)ERVP16; (B) pVitBx2 and pGAL1-ER; or pVitBx2, pGAL1-ER and pHCA/GAL4(1-93)ERVP16; (C) p416GAL1-lacZ and p414GAL1-GAL4ERVP16; (D) p416GAL1-lacZ and p415GAL1-GAL4ERVP16. All cultures were grown in the presence of glucose except when "gal" is written, indicating galactose-containing cultures. In all cases, 5 ml cultures were inoculated from a mid-log preculture to an O.D. (600 nm) of 0.02, and incubated for 14 hours at 30°C in the presence or the absence of 1 μM β-estradiol. Average and standard deviation of at least three independent experiments are represented. Induction represents the ratio between β-galactosidase activities (in the presence and in the absence of β-estradiol). Basal increase was calculated dividing the β-galactosidase activity detected in the absence of hormone, by the activity exhibited by cells cultured in the same conditions, containing the same target reporter construct, but lacking any estrogen-dependent transactivator. Regulation efficiency was calculated dividing induction by basal increase.