CYP102 (Cytochrome P450 B M - 3 ) is induced inBacillus megateriumby barbiturates, peroxisome proliferators, and nonsteroidal anti-inflammatory drugs. We now describe the induction of CYP102 inB. megateriumby 17β-estradiol and by 4-sec-butylphenol. These estrogens interact with the repressor protein Bm3R1, causing it to dissociate with the operator of theCYP102gene and allowing transcription to occur. We have developed a stable transfection of a construct intoB. megateriumof a truncatedCYP102gene coupled with the luciferase gene in a promoterless plasmid and have used this construct to test the induction of CYP102 by these estrogens. Estradiol demonstrated a dose-dependent induction of CYP102 which saturated at a 2-fold increase at 150 μM 4 hr post-addition. 4-sec-Butylphenol produced a dose-dependent and time-dependent induction up to 300 μM and 6 hr post-induction.