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