Transcript Foundations of Biology - Geoscience Research Institute

James 4:7
7 Submit yourselves
therefore to God.
Resist the devil, and
he will flee from you.
©2000 Timothy G. Standish
Regulation of
Transcription
Timothy G. Standish, Ph. D.
©2000 Timothy G. Standish
Eukaryotic RNA Polymerase II
Promoters
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 Promoters
5’
Promoter
Exon 1
Sequence elements
TATA
~200 bp
Some sequence
elements are also
response elements
©2000 Timothy G. Standish
Response 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
Elements
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 Response
Hot
HSTF Kinase
Cool
Heat shock genes
Heat shock response elements
©2000 Timothy G. Standish
The Heat Shock Response
Hot
HSTF Kinase
Cool
Activation of
kinase
Phosphorylation
of HSTF
Heat shock response elements
©2000 Timothy G. Standish
The Heat Shock Response
Hot
Activation of
HSTF
Kinase
HSTF
Cool
Transcription initiation
of all heat shock genes
with HSEs
Heat shock response elements
©2000 Timothy G. Standish
Metallothionein 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 Regulation
Glucocorticoid Response
Element - Behaves as an
enhancer and allows regulation
by steroids
GRE
-260
-240
BLE
-220
-200
-180
TGACTCA
A consensus sequence to which
AP1 binds conferring a
response to phorbol esters
MRE
-160
Basal Level Elements
(needed for transcription,
act as enhancers)
MRE
-140
BLE TRE
-120
-100
MRE GC
-80
-60
Metallothionein Regulator
Elements - Multiple copies
confer greater levels of
induction by heavy metals
MRE
TATA
-40
-20
Constitutive
Elements
©2000 Timothy G. Standish
Regulation 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
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 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 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 Fingers
O
H2N
C
C
H
H 2N
OH
C
H
C
H
H
C
H
C
OH
C
H
H
C
HS
O
N H
N C
©2000 Timothy G. Standish
Zinc Fingers
≈6
Amino
acids
C H
Zn++
C H
2- 4
Amino
acids
C H
≈ 23
Amino
acids
C H
Zn++
Zn++
C H
C H
7 - 8 Amino acid linker
©2000 Timothy G. Standish
©2000 Timothy G. Standish