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James 4:7 7 Submit yourselves therefore to God. Resist the devil, and he will flee from you. Regulation of Transcription. Timothy G. Standish, Ph. D. Eukaryotic RNA Polymerase II Promoters. - PowerPoint PPT Presentation
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©2000 Timothy G. Standish
James 4:7
7 Submit yourselves therefore to God. Resist the devil, and he will flee from you.
©2000 Timothy G. Standish
Regulation of Regulation of TranscriptionTranscription
Timothy G. Standish, Ph. D.
©2000 Timothy G. Standish
Eukaryotic RNA Polymerase II Eukaryotic RNA Polymerase II PromotersPromoters
Eukaryotic promoters are made up of a number of sequence elements spread over about 200 bp upstream from the transcription start site
In addition to promoters, enhancers also influence the expression of genes
Control of gene expression in eukaryotes involves many more factors than control in prokaryotes
This allows much finer control of gene expression
©2000 Timothy G. Standish
Eukaryotic PromotersEukaryotic Promoters
5’ Exon 1Promoter
~200 bp
TATA
Sequence elements
Some sequence elements are also response elements
©2000 Timothy G. Standish
Response ElementsResponse Elements Response elements are short sequences found
either within about 200 bp of the transcription start site, or as part of enhancers
Different genes have different response elements Binding of transcription factors to response
elements determines which genes will be expressed in any cell type under any set of conditions
©2000 Timothy G. Standish
Heat Shock Response Heat Shock Response ElementsElements
Sudden changes in the temperature of cells cause stress in response to which heat shock genes are expressed
At least some heat shock genes are thought to be chaperones that help proteins fold correctly
Heat shock genes have Heat Shock Elements (HSEs) in their control regions
Heat Shock Transcription Factors (HSTFs) bind the HSEs up regulating expression of heat shock gene products
©2000 Timothy G. Standish
The Heat Shock ResponseThe Heat Shock Response
HSTFHot
Cool
Kinase
Heat shock genes
Heat shock response elements
©2000 Timothy G. Standish
The Heat Shock ResponseThe Heat Shock Response
HSTFHot
Cool
KinaseActivation of kinase
Phosphorylation of HSTF
Heat shock response elements
©2000 Timothy G. Standish
Heat shock response elements
The Heat Shock ResponseThe Heat Shock Response
Hot
Cool
Kinase
Activation of HSTF
HSTF
Transcription initiation of all heat shock genes
with HSEs
©2000 Timothy G. Standish
Metallothionein RegulationMetallothionein Regulation Heat shock protein regulation illustrates how a group
of genes can be regulated by a single transcription factor
Other genes are regulated by a group of transcription factors which allows them to either respond to multiple separate situations, or respond only to a specific combination of situations
Metallothionein is an example of a gene that can be turned on by multiple transcription factors
©2000 Timothy G. Standish
Metallothionein RegulationMetallothionein Regulation
-260 -240 -220 -200 -180 -160 -140 -120 -100 -80 -60 -40 -20
BLE GC TATAGRE MRE MREMRETREMREBLE
Basal Level Elements(needed for
transcription, act as enhancers)
Glucocorticoid Response Element - Behaves as an
enhancer and allows regulation by steroids
Constitutive Elements
Metallothionein Regulator Elements - Multiple copies
confer greater levels of induction by heavy metals
TGACTCAA consensus sequence to
which AP1 binds conferring a response to phorbol esters
©2000 Timothy G. Standish
Regulation By TFsRegulation By TFs A single transcription factor (or group of transcription
factors) may regulate expression of a group of genes (i.e., heat shock proteins)
A single gene may be regulated by a number of independent transcription factors (i.e., metallothionein)
Eukaryotic regulation does not seem to involve repression To achieve high levels of expression, several different
transcription factors binding to different response elements may be necessary
©2000 Timothy G. Standish
How Do TFs Recognize How Do TFs Recognize Response Elements?Response Elements?
Some mechanism must exist for protein transcription factors to recognize the specific sequences of bases found in response elements
There is no known specific relationship between a given amino acid and a base that would allow direct recognition
Groups on bases that are not involved with base pairing have the potential to be recognized by proteins
Some specific sequences are known to influence the gross structure of DNA
©2000 Timothy G. Standish
DNA Binding DomainsDNA Binding Domains Transcription factors exhibit a number of different
motifs found in the area known to bind DNA: Zinc finger -First found in TFIIIA Helix-turn-helix - First described from phage receptors Amphipathic Helix-loop-helix - Identified in some
development regulators Leucine zipper - Held together by interactions between
leucine amino acids
©2000 Timothy G. Standish
Zinc FingersZinc Fingers Are found in steroid receptors and are common in other
transcription factors Interaction between cysteine and histidine amino acids
and the divalent zinc ion results in the formation of loops called “fingers”
One side of each loop forms an a-helix which can lie in the major grove of DNA
Interaction between the amino acids in the zinc finger and bases in the DNA allow for sequence recognition
©2000 Timothy G. Standish
Zinc FingersZinc Fingers
OH
H
H
O
HS
H
H2N
C
C
C
OH
H
H
O
N
H
H2N
C
C
C
CH
C
C
N H
©2000 Timothy G. Standish
Zinc FingersZinc Fingers
Zn++
H
H
C
C
Zn++
H
H
C
C
Zn++
H
H
C
C
≈ 23Aminoacids
7 - 8 Amino acid linker
2- 4 Aminoacids
≈ 6 Aminoacids
©2000 Timothy G. Standish