El papel de la curvatura de DNA en la regulación
Clues and consequences of DNA bending in transcription
• Nature of DNA bending. Bendability vs curved DNA• Clues of DNA bending
– Inducer/ inhibitor of protein-DNA interactions– Catalyst of protein-protein interactions– DNA chaperones
• Consequences of DNA bending– Channeling signals through promoter architecture– Helping response-amplification signals– Avoiding transcriptional promiscuity
• DNA bending: A new signal-transduction mechanism?
Curved DNA
Wedge model Structural discontinuitiesmodel
Bendability
• Bendability: the ability of specific short sequences to assume preferentially conformations that accommodate the deformation associated with protein-induced bending.
Bendability vs curved DNA
• Curved DNA is deformed even in the absence of external forces, thereby resulting in a very rigid structure.
• Bendable DNA allows a mixture of many different conformational states, the equilibrium of which can be displaced toward one specific form by external forces such as proteins interacting with them.
Protein-mediated DNA bending
• Neutralization of charges in the DNA backbone
• Setting up extended protein-DNA contacts
• Intercalation of protein side chains in the minor groove
Bend DNA is important for DNA-protein interactions
• CAP: Correlation between bendability of CAP site and the affinity of the protein (Gartenberg and Crothers, 1988)
• Bacterial 70-RNA polymerase induces a strong bend in the promoter upon binding (Pérez-Martín and Espinosa, 1994)
• TBP and holo-TFIID bend DNA (Starr et al., 1995)
Clues of DNA bending in transcription
• Inducer/ inhibitor of protein-DNA interactions• Catalyst of protein-protein interactions• DNA chaperones
DNA bending as an inducer or inhibitor of DNA-protein
interactions• Structural synergy:
– Pre-curved CAP DNA binding sites– HMG1 and the human progesterone receptor
• Structural inhibition:– Out of phase RepA-induced bends
Structural synergy at the CAP-binding sites (Kahn and Crothers, 1992)
Structural synergy between HMG1 and PR (Oñate et al., 1994)
HMG1
PR
Structural inhibition (Pérez-Martín and Espinosa, 1991)
RNApolRNApol
RNApolRNApol+ RepA
Clues of DNA bending in transcription
• Inducer/ inhibitor of protein-DNA interactions• Catalyst of protein-protein interactions• DNA chaperones
DNA bending as a catalyst of protein-protein interactions
• Long distances: – IHF– histones
• Short distances:– bendability: XylR
enhancer– extra factors: LEF-
1 enhancer
Distance (bp)
|10
|100
|1000
Free
ene
rgy
XylR enhancer (Pérez-Martín and de Lorenzo, 1996)
30 bp
ATP
Bendable DNA
LEF-1 enhancer in TCR (Giese et al., 1992)
LEF-1
PEBP2
Ets-1
ATF/CREB
DNA bending as a catalyst of protein-protein interactions
• Long distances: – IHF– histones
• Short distances:– bendability: XylR
enhancer– extra factors: LEF-
1 enhancer
Distance (bp)
|10
|100
|1000
Free
ene
rgy
IHF at Pu promoter (Pérez-Martín and de Lorenzo, 1996)
XylR54-RNAP
54-RNAPIHF
>200 bp
Nucleosome positioning at the Drosophila hsp26 promoter (Thomas
and Elgin, 1988)
TATA boxHSTF-box GAGA-boxGAGA-box HSTF-box
-100-200-300-400
RNApolIInucleosome
Clues of DNA bending in transcription
• Inducer/ inhibitor of protein-DNA interactions• Catalyst of protein-protein interactions• DNA chaperones
DNA chaperones (Travers, 1994)
• DNA chaperones are DNA-bending proteins that stabilize an otherwise loose structure in a particular conformation which sustains the assembly of additional proteins into a higher-order complex, being displaced away from the DNA in the final assembly.
DNA chaperones: HMG1 and PR (Oñate et al., 1994)
PR HMG1
DNA chaperones: HU at Ps promoter (Pérez-Martín and de Lorenzo, 1995)
54-RNAPXylR
54-RNAPHU
54-RNAP
Consequences of DNA bending in transcription
• Channeling signals through promoter architecture
• Helping response-amplification signals• Avoiding transcriptional promiscuity
Channeling signals through promoter architecture
• Co-activation– CAP and MalT– nucleosome in Xenopus vitellogenin B1 promoter
• Anti-repression– CAP in ParaBAD
• Anti-induction– YY1 in c-fos promoter– IHF in nac promoter
cAMP
Co-activation: MalT and CAP at PmalE-PmalK in E.coli (Richet et al., 1991)
PmalE
PmalK
RNApol
RNApol
MalTCAP
Maltose
Co-activation: Xenopus vitellogenin B1 promoter (Schild et al., 1993)
Oestrogenreceptor
RNApolIIHNF3NF1Hormone
Cell-type
Anti-repression: AraC and CAP at ParaBAD in E.coli (Lobell and Schleif,
1991)
RNApol
RNApol RNApol
AraC
CAPcAMP Arabinose
Anti-induction: YY1 at the c- fos promoter (Natesan and Gilman, 1993)
CREBP
YY1RNApolII
cAMP
Cell status
Anti-induction: Nac at the nac promoter from K. aerogenes (Feng et al., 1995)
PnacRNApol
HU
Nac
NtrC
Nitrogenstatus Nac levels
Consequences of DNA bending in transcription
• Channeling signals through promoter architecture
• Helping response-amplification signals• Avoiding transcriptional promiscuity
DNA bending in response-amplification
mechanisms
Stimulation of lysis/lisogeny of phage Mu by DNA bending (Goosen, van de Putte, 1995)
O1 IHF O2 O3Pe
RNApol Pe
O1
O2 O3LYSIS LYSOGENY
Consequences of DNA bending in transcription
• Channeling signals through promoter architecture
• Helping response-amplification signals• Avoiding transcriptional promiscuity
DNA bending and transcriptional promiscuity
• Mechanisms to suppress non-specific activation at enhancers: restrictors
? ?
Restrictor: a new role of IHF in Pu promoter (Pérez-Martín and de Lorenzo,
1995)XylR
IHF54-RNAP
IHF54-RNAP
+IHF54-RNAP
-IHF
Clues and consequences of DNA bending in transcription
DNA bending: A new signal-transduction mechanism?
Characteristics of signal-transduction mechanisms
• Integration of signals• Amplification of signals• Specificity of signals
Integration of signals
Kinase3
Kinase2
Kinase1SignalA
SignalB
SignalC
Characteristics of signal-transduction mechanisms
• Integration of signals• Amplification of signals• Specificity of signals
Amplification of signals
Kinase2
Kinase1
Kinase2
Kinase3Kinase3 Kinase3Kinase3
Characteristics of signal-transduction mechanisms
• Integration of signals• Amplification of signals• Specificity of signals
Specificity of signals(Scaffolding)
Kinase3
Kinase2
Kinase1
SignalA SignalB
Kinase3
Kinase2
Kinase1
Designing promoters “ a la carte”
Integration
AmplificationSpecificity
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