1. The lac operon of the Escherichia coli bacterium - Positive transcriptional control of the lac operon by the polymerase transactivator protein cAMP-CAP - Animation©E.Schmid/SWC2002

2. Scenario 1  both, glucose and lactose, are available for the cell

3. lacIPOlacZlacYlacA lac operon no transcription ! Glucose + Lactose + Escherichia coli (E.coli) RNApolymeraseRepressor Glucose metabolism

4. lacIPOlacZlacYlacA no transcription ! Glucose + Lactose + Escherichia coli (E.coli) Lactose binding & Conformational change Porin

5. lacIPOlacZlacYlacA low transcription rate Glucose + Lactose + Escherichia coli (E.coli) Dissociation of lac repressor

6. Scenario 2  glucose level drops  no glucose for metabolism available

7. lacIPOlacZlacYlacA low transcription rate! Low glucose Lactose + + glucose sensor

8. lacIPOlacZlacYlacA low transcription rate! no glucose Lactose + + Adenylatecyclase

9. lacIPOlacZlacYlacA low transcription rate! no glucose Lactose + ATP cAMP

10. lacIPOlacZlacYlacA low transcription rate! no glucose Lactose + cAMP binding + cAMP-CAP

11. lacIPOlacZlacYlacA low transcription rate! no glucose Lactose + cAMP DNA binding

12. lacIPOlacZlacYlacA high transcription rate! no glucose Lactose + cAMP POL transactivation +

13. lacIPOlacZlacYlacA high transcription rate! no glucose Lactose + cAMP mRNA