L3 - How do TFs regulate txn? Flashcards
What activators bind to TFIID to assist its recruitment?
Sp1, p53, c-Jun
What did ChIP-PCR show about p53?
Binds TBP, TAF as well as coactivators p300 and mediator
What was shown in yeast?
Activator bypass
What is the process of activator bypass in yeast?
DNA sequence recognised by DBD of LexA protein 45bp from TATA
Txn activated by LexA DBD fused to activation domains of TFs (eg MyoD)
Txn can also be activated by LexA DBD fused to TBP
(direct recruitment of TBP by LexA DBD bypasses normal requirement for txn activator)
What is the relationship between TAL1 and T-cell acurte lymphoblastic leukemia?
- Small mutations upstream of TAL1 create binding sites for TF that recruits HAT CBP
- Creates super enhancer that drives expression of TAL1 oncogene
- TAL1 is a TF that provides + feedback
What conformational changes do activators cause?
Induce rearrangement of mediator to expose surface where pol 2 binds
Cause reaaragment in TFIIB that expose binding surface for pol 2 and F
What is the assembly of the PIC stimulated by?
activators, coactivators and chromatin remodellers
What can be rate limiting in activation and example?
Steps subsequent to pol 2 recruitment
Activated mouse B cells activated - gene occupancy by pol 2 increases 1.7 fold but mRNA expression only increases 11.7 fold
What expression is induced when mouse B cells are activated?
TFIIH (catalyses promoter opening nd phos of pol2 ctd on ser5
What else can be rate limiting for transcription?
Escape from promoter
What stimulates promoter escape and what is it?
P-TEFb
cdk9/cyclin T complex
How is promoter escape stimulated?
NELF + DSIF bind pol 2, pausing initiation
P-TEFb phos DSIF causing release of NELF and txn
p-TEFb phos Ser2 on CTD
What is NELF and how does it change?
A repressor but phosphor of DSIF converts it to elongation activator
Why is txn paused?
Help keep promoter depleted of nucleosomes
Allows rapid induction of genes (after heat shock)
Provides for capping of transcript
What does MYC do?
recruits HATs, TBP, TFIIH and P-TEFb to target genes
Can stimulate both pre and post initiation steps in txn
What disease was amplification of MYC frequent in?
Hepatocellular carcinoma (HCC) (liver cancer)
What is the SEC?
Super elongation complex - Complex of proteins that timulate transcript elongation by pol II
How is the SEC involves in leukaemias?
SEC subunits often fused to MLL1 gene through chromosomal translocation
Results in aberrant exp including upreg of HOX genes
What is DOT1L?
a methyltransferase in SEC
What is DOT1L’s function?
Mono- di-, and trimethylating H3K79 as pol 2 transcribes
How is DOT1L involved in treatment of leukaemias?
Required for development driven by MLL1 translocations so inhibitor has entered clinical trials
What does EXH2 do?
A histone methyltransferase that repressed txn by trimethylating H3 on lys27
How is EZH2 involved in cancers and how is it treated?
In lymphomas it is frequently activated
A drug that inhibits eradicates lympohmas in mice
How is DNA methylation involved in cancer?
Silences tumour suppressor genes
What on average is the ratio of mRNA to its protein?
1:900
