lacZ lacY lacAOAi

Repressor lactose lactose/repressor RNA pol CRP cAMP CRP/cAMP

complex CAP complex

B-galactosidase

lactose permease

transcetylase

operatoractivatorRegulatory gene

P

lacZ lacY lacAOAi

NO transcription

lacZ lacY lacAOAi

NO transcription

lacZ lacY lacAOAi

Transcription occurs

lacZ lacY lacAOAi

Lac operon

Not taken up

Lots of glucose

Repressor lactose lactose/repressor RNA pol CRP cAMP CRP/cAMP

complex CAP complex

IIC

glycolysis

Glucose

PEP

Pyruvate

Kreb’s

IIB

HPr

IIA

EI ATP

glucose

glucose

lactose

Low cAMP

Repressor lactose lactose/repressor RNA pol CRP cAMP CRP/cAMP

complex CAP complex

IIC

glycolysis

Glucose

PEP

Pyruvate

Kreb’s

HPr

IIA

EI ATP

IIB

lactose

Adenylate cyclase

Not more glucose

This process slows down

Levels of cAMP increase

Repressor lactose lactose/repressor RNA pol CRP cAMP CRP/cAMP

complex CAP complex

IIC

glycolysis

Glucose

PEP

Pyruvate

Kreb’s

HPr

IIA

EI ATP

IIB

lactose

Adenylate cyclase

Not more glucose

This process slows down

lacOp becomes active