Page 128 - Color Atlas of Biochemistry

Metabolic Regulation 119

A. Functions of regulatory proteins

Negative regulation Positive regulation

Without ligand With ligand Without ligand With ligand

RNA mRNA
poly- RNA
merase poly-
merase

DNA Gen
Inducer Promoter
L
Repressor Ligand L
1a 1b 3a 3b

L
L

2a 2b 4a 4b

B. Lactose operon

Genes for 5'
Catabolite permease CH Adenin
activator 2
protein Promoter galactosidase O O
(CAP) CAP transacetylase O H H
P H H
3'
O O OH
CAP-binding Operator
1. site

RNA polymerase Recognition cAMP
(only binds in the helix
presence of
CAP · cAMP)

Lactose
lac Repressor
2.

cAMP Lactose catabolism
Glucose
mRNA

CAP · cAMP Transcription

Repressor
Lactose allo-
lactose
Allolactose complex
3. 4. CAP · cAMP bound to DNA

Koolman, Color Atlas of Biochemistry, 2nd edition © 2005 Thieme
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