Eukaryotic transcription Flashcards
If the eukaryotic RNAP II holoenzyme isn’t sufficient to initiate transcription on its own, what else is required?
General transcription factors (GTFs)
How can GTFs be a point of gene regulation?
Many regulatory elements interact with them
What are the 7 GTFs needed for RNAP II to initiate transcription?
- TFIIA
- TFIIB
- TFIID/TBP
- TFIIE
- TFIIF
- TFIIH
- The mediator complex
What is the pre-initiation complex (PIC)?
RNAP II + all 6 GTFs at the promoter
What are the two models of the assembly of the pre-initiation complex?
- An assembly cascade where certain components are already binding to the promoter, and assemble in a certain order
- Partial assembly before promoter binding
What are the 4 functions of the GTFs?
- Recognize and bind to the core promoter elements
- Recruit RNAP II to the promoter and help it position itself
- Initial melting around the +1 nucleotide and promoter clearance
- Interact with regulatory factors
What does TFIIF do?
- Binds to free RNAP II and prevents it from binding to DNA by itself
- Interacts with TFIIB and stabilizes RNAP II at the promoter
What does TFIID do?
Recognize and bind to the core promoter elements - TATA boxes and other elements. It will be the first GTF to bind to the promoter
What is the difference between TFIID and TBP?
TBP is a subunit of the TFIID protein. It binds to a TATA box and the rest of the GTF will follow
Can TFIID still bind to a promoter that doesn’t have a TATA box?
Yes, it has other subunits that bind to other regulatory elements
What were the results of the Tijan et al. 1995 study on the role of TBP vs the entire TFIID protein?
When the TATA box was the only core promoter element, TBP alone worked as well as the whole protein to initiate transcription. When the TATA box was paired with other promoter elements, the whole TFIID protein worked better than TBP alone
What does TFIIA do?
- Initial promoter recognition in some promoters
- Interacts with TBP and stabilizes its binding to the TATA box
- Is an activator, but isn’t necessary for transcription to start
What does TFIIB do?
- Bind to DNA non-specifically
- Binds to TFIID and stabilize it
- Directly interacts with RNAP II, recruits it to the promoter, and positions it at the promoter
What does the mediator do?
- Transcriptional coactivator, multiprotein complex
- Associates with the GTFs and the C-term of RNAP II
- Bridges the PIC to other TFs besides the GTFs
- Required for transcription to occur in most RNAP II promoters
What does TFIIH do?
- DNA helicase activity
2. Kinase activity to phosphorylate RNAP II so it becomes elongation competent