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

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)

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 hill.com/olc/dl/120080/bio27.swf iewkey=712c49d51a18a32b39f0