5 - Initiation of RNAPs Flashcards
What is the eukaryotic PIC composed of?
General transcription factors (GTFs)
What is TFIID?
Transcription factor for RNA pol II D is the first thing to bind to the promoter.
It is a large complex made up of the TAT-box Binding Protein (TBP) and 14-18 TBP Associated Factors (TAFs)
What is TBP?
A universally conserved protein that binds and reshapes the promoter DNA at the TATA box, acting as a nucleation point for GTFs and thus determining the TSS.
What is the second TF to bind the promoter, and what role does it have?
TFIIA
Stabilises the TFIID:DNA complex
What is the third TF to bind the promoter, and what role does it have?
TFIIB
Helps TBP with TAT-box reshaping, thus promoting open complex formation and TSS determination.
TFIIB eventually interacts with Pol II
What is the third TF to bind the promoter, and what role does it have?
TFIIF - RNA Pol II
TFIIF is bound to the RNAP and recruits it to the complex through its interaction with the existing proteins.
This leads to a rearrangement of the complex as it existed.
What is the fourth TF to bind the promoter, and what role does it have?
TFIIE
This seems to have little effect other than recruiting the next transcription factor, but might be involved in stabilising the non-template DNA strand.
What is the fifth TF to bind the promoter, and what role does it have?
TFIIH
This is a large complex with several functions. It has bi-directional helicase activity and is also a kinase that activates the Pol II
What signalling modification activates Pol II during initiation?
TFIIH phosphorylates the Pol II Carboxy-Terminal Domain at Serine-5
What is the overall order of binding to the promoter to form the PIC?
TFIID TFIIA TFIIB TFIIF - Pol II TFIIE TFIIH
How active is the RNAP with just the PIC TFs?
Not very, this is called the basal transcription complex as alone it is responsible only for a very low level of transcription. To obtain a reasonable rate of transcription there must be enhancers, other TFs etc involved.
