Regulation of gene expression in prokaryotes Katalin Kiss Dept. of Medical Biology 12.11. 2007

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