Upload
jocelyn-chambers
View
229
Download
0
Tags:
Embed Size (px)
Citation preview
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