what are the structural features of transcriptional activator and repressor proteins.Give an example of how they work. What are the transcriptional...

Transcriptional activators are proteins that bind to DNA
and stimulate transcription of nearby genes. Most activators enhance RNA polymerase
binding (formation of the closed complex) or the transition to the open complex required
for initiation of transcription. Most activators interact directly with a subunit of RNA
polymerase. Some examples
follow:

• Regulation of the arabinose
  regulation by href="http://www.sci.sdsu.edu/~smaloy/MicrobialGenetics/topics/regulation/AraC.html">AraC
  
  


• Catabolite
  repression by href="http://www.sci.sdsu.edu/~smaloy/MicrobialGenetics/topics/regulation/CRP.html">cAMP-CRP

Coactivators
are diverse and multifunctional proteins that act downstream of DNA-binding activators
to stimulate transcription. Recent studies elucidate the temporal sequence in which
coactivators are recruited to target promoters, and how their enzymatic properties and
molecular interactions culminate in transcriptional initiation.
Examples:

ACF – ATP-utilizing chromatin
assembly and remodeling factor
AD – activation
domain
ATM – ataxia telangiectasia
mutated
CARM1 – coactivator-associated arginine
methyltransferase 1
CATD – cathepsin
D
CBP – CREB-binding
protein
ChIP – chromatin
immunoprecipitation
CREB – cAMP response element
binding protein
CTD – carboxy-terminal domain (of
RNA pol II)
ER – estrogen
receptor
GTF – general transcription
factor
HAT – histone
acetyltransferase
IFN-β – interferon
β
P/CAF – p300/CBP-associated
factor
PIC – preinitiation
complex
PKA – protein kinase
A
PKC – protein kinase
C
PRMT1 – protein arginine methyltransferase
1
RNA pol II – RNA polymerase
II
SAGA – Spt-Ada-Gcn5-acetyltransferase
complex
TAF – TBP-associated
factor
TBP – TATA-binding proteinDNA is packed
into chromatin and transcriptionis dependent upon activators that recruit other factors
toreverse the repressive effects of chromatin. The response toactivators requires
additional factors referred to as coactivators.One such coactivator, mediator, is a
multi-subunit complex capable of responding to different activators. It plays an keyrole
in activation, bridging DNA-bound activators, the generaltranscriptional machinery,
especially RNA polymerase II, andthe core promoter. Its subunits are necessary for a
varietyof positive and negative regulatory processes and serve asthe direct targets of
activators themselves. In vivo and invitro studies support various roles for mediator in
transcriptioninitiation, while structural studies demonstrate that it engagesin multiple
interactions with RNA polymerase II, and adoptsconformations that are activator
specific.
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