lacI              Prom          lacO ATG                                               STOP
No T7 or
 Target Protein expressed
  lacI              Prom         lacO ATG                                                STOP
- IPTG
+ IPTG
T7 and
Target protein expressed

Auto-induction
cAMP
CRP
LacI
Lactose
Lactose
Permease
β-Gal
Prom      lacZ    lacY
Lactose to
Allolactose
Glucose
» Early energy source
» Repression
Glycerol
» Late energy source
Lactose
» Induction
Extracellular
Intracellular
   Glucose
Bacterial Genome
Lactose
lacI
X
Glycerol