Transcription factors

1
Transcription factors

• 1. Basal factors involved in initiation of RNA
  synthesis of all pol II promoters. Form the
  preinitiation complex.
• 2. Upstream factors (transactivators,
  transfactors) bind upstream elements, specific
  to different promoters.
• Inducible factors a type of upstream factor
  that controls highly regulated (inducible)
  transcription binds to a response element.

RNA pol II, TBP (TFIID), TFIIB, A, F, E, H
basal factors
upstream factors
TATAA
RE
2
RNA polymerases in the Eukaryotic cell
1. RNA pol I transcribes ribosomal genes
accounts for most cellular RNA synthesis.
Resides in the nucleolus. 2. RNA pol II
transcribes genes encoding proteins accounts for
most of the remaining activity in the cell.
Sensitive to a-amanitin. Largest subunit has 7 aa
repeats in its C-terminal domain (CTD) 26 in
yeast, 50 in mammals. ?, ?, and a homologies in
3 largest. 3. RNA pol III transcribes tRNA
genes and other small RNAs minor activity in the
cell.
All have from 8-14 subunits All can transcribe
DNA non-specifically in vitro, but promoter
recognition depends on transcription factors.
3
The eukaryotic promoter for RNA pol II
intron
-200 bp
RNA
exon
1
3
-3
5
TATAA -30 bp
Initiator (Inr)
splicing
5
upstream element
3
CAAT box, GC box these often present in
mammalian genes
mRNA
-45
20
minimal promoter
4
The eukaryotic promoter for RNA pol II
core promoter
-200
1
TATAA -30 bp
Initiator
upstream element
upstream element
-45
20
minimal promoter
5
Organization of cis-acting elements

• 1. cis-elements may be located upstream,
  downstream, or in introns. Most commonly found
  upstream.
• 2. elements may be scattered is distribution, or
  organized in clusters called enhancers.

Scattered distribution
Init
TATAA
upstream elements
6
Organization of cis-acting elements

• 3. enhancers contain modules or domains which
  consist of cis-elements. These may be all the
  same, or a combination of different elements.
• 4. enhancers and individual cis-elements may be
  over 1,000 bp distant, and can function in either
  orientation.

Enhancer
Init
TATAA
modules
7
Transcription factors

• 1. Basal factors involved in initiation of RNA
  synthesis of all pol II promoters. Form the
  preinitiation complex.
• 2. Noninducible Upstream factors
  (transactivators, transfactors) bind upstream
  elements, specific to different promoters.
• Inducible factors a type of upstream factor
  that controls highly regulated (inducible)
  transcription binds to a response element.

basal factors
RNA pol II, TBP (TFIID), TFIIB, A, F, E, H
upstream factors
TATAA
RE
8
Types of Transcription
1. Basal low level background activity, not
regulated, only requires a minimal promoter, no
involvement of upstream elements ( other
cis-elements) or transactivator proteins. 2.
Activated requires upstream (or other locations)
cis-elements, usually much higher levels of
activity than basal transcription.
upstream factors
Activated transcription requires upstream factors
TATAA
9
Recruitment of basal factors
Activated transcription
TFIIB
transactivator protein
TBP
1
TATAAA
transcription
upstream element
TATA box
Key step in activated transcription performed by
activator proteins.
10
Recruitment of basal factors
Activated transcription
transactivator protein
RNA polymerase
1
TATAAA
transcription
11
Recruitment of basal factors

• Preinitiation complex

Activated transcription
transactivator protein
RNA polymerase
1
TATAAA
transcription
12
Recruitment of basal factors
Activated transcription

• transcriptional initiation

transactivator protein
1
TATAAA
transcription
13
Recruitment of basal factors
Activated transcription

• elongation

transactivator protein
mRNA
1
TATAAA
transcription
TFIID remains at the promoter for next round of
initiation.