Regulation of transcription in prokaryotes

Control of development of phage SPO1 by changing sigma factors

Transcription factorsregulate rates oftranscription

Activation of transcription by allostery

Cooperative binding of transcription factors

Cooperative effect of binding of transcription factors

Structure of the E. coli lac operon

Examples: the E. coli lac operon

Transcription of the lac operonis affected by lactose andglucose

Figure 14.7b Genomes 3 (© Garland Science 2007)

Figure 14.7a Genomes 3 (© Garland Science 2007)

Diauxie

Figure 14.7c Genomes 3 (© Garland Science 2007)

Catabolite repression CAP = catabolite activator protein

Transport of glucose dephosphorylates protein IIAGlc.Protein IIAGlc also inhibits lactose permease.

Lac operon sequences covered by RNA polymerase and transcription factors

Contact between RNA polymerase and the cataboliteactivator protein (CAP)

CAP recruits RNA polymerase to the lac promoter

Carboxy terminal domain Non- template domain

CAP binds to DNA as a homodimer via a helix-turn-helix DNA-binding motif

CTD of RNA polymerase

DNA

CAP

cAMP induces conformational changes in CAP

CAP only binds to DNA in the presence of cAMP

Note: CAP affects expression of more than 100 genes inE. coli

The Lac repressor binds as a tetramer

Reagents used in transcription from the lac promoter

Transcription factorsregulate rates oftranscription

Activation of transcription by allostery

Allosteric control of transcription

Examples: transcription factors NtrC and MerR

NtrC induces a conformational change in the RNA polymeraseby interacting with sigma 54

MerR induces a conformational change in the DNA promoter regionwhen bound to mercury

Simultaneous binding of RNA polymerase and MerR

Depending on the presence of arabinose, AraC binds to different sites on the DNA

The araBAD operon is regulated by cooperative binding oftranscription factor AraC

CAP binding site

Example: Regulation of the lytic and lysogenic infection cycle of bacteriophage lambda

The circularized genome of bacteriophage lambda

Region of the lambda genome that controls lytic andlysogenic growth

Promoter activities during lytic and lysogenic growth

Strong promoters

Weak promoter

Binding sites for CI and Cro

CI binding sitesCro binding site

Binding of CI and Cro regulate growth of lambda

Cooperative binding

Repressor establishment upon infection is mediatedby activator CII

The level of activator CII controls transcription of repressor CI and of the integrase gene

Poor growth conditionsand high lambda concentrationlead to elevated concentrationsof CII

Antiterminator proteins N and Q control transcription ofearly genes

Antiterminator proteins N and Q control transcription ofearly genes

Binding site of Q protein

N binds to the RNA transcribed from BoxA/B

Transcripts from PI and PL have different 3’ ends that confer different mRNA stability

Transcripts from PI and PL have different 3’ ends that confer different stabilities to mRNA