Regulation of gene expression in prokaryotes
Katalin Kiss Dept. of Medical Biology
12.11. 2007.
Gene expression in prokaryotes
• Types of expression:– Constitutive expression (eg. genes of glucose
utilizing enzymes)– Regulated expression
• induction (eg. genes of catabolic enzymes)• repression (eg. genes of biosynthetic enzymes)
• Significance of regulation: adaption to changes in enviroment (eg. nutrient supply), „feedback”
• Level of regulation during gene expression: mostly transcription (activity of RNA polymerase) is regulated
• Mechanism of regulation: operon model
Operon model
Francois Jacob and
Jacques Monod
(Nobel-prize 1965.):Study of E.coli bacterium
Regulation of gene expression at the level of transcription
Operon theory
Operon
Components:– Regulated genes = structural genes
(transcribed as a polycystronic mRNA)– Promoter– Operator
Types:– Inducible– Repressible
Regulatory elements of operon
• DNA sequences = „cis-acting elements” (operator, promoter)
• Regulatory proteins = „trans-acting elements” (activator, repressor)
• Effectors (inducer, corepressor)
Lactose operon (lac operon)
RNA polymerase
lactose
CAP
Regulatory elements of Lactose operon (Lac operon)
• Cis-acting elements: operator, promoter
• Regulatory proteins: Lac-repressor and CAP
• Effectors: lactose and cAMP = inducers
Triptophan operon (Trp operon)
Triptophan operon (Trp operon)
Alberts Fig. 7-34
Attenuation of Triptophan operon (Trp operon)
Regulatory elements of Tryptophan operon (Trp operon)
•Cis-acting elements: operator, promoter, attenuator
•Regulatory proteins: Trp-repressor
•Effectors: trp= korepresszor
Animations of Lac operon and Trp operon on the web
• http://highered.mcgraw-hill.com/olc/dl/120080/bio27.swf
• http://www.dnatube.com/view_video.php?viewkey=712c49d51a18a32b39f0