L3 - How do TFs regulate txn?

Question 1

What activators bind to TFIID to assist its recruitment?

Answer 1

Sp1, p53, c-Jun

Question 2

What did ChIP-PCR show about p53?

Answer 2

Binds TBP, TAF as well as coactivators p300 and mediator

Question 3

What was shown in yeast?

Answer 3

Activator bypass

Question 4

What is the process of activator bypass in yeast?

Answer 4

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)

Question 5

What is the relationship between TAL1 and T-cell acurte lymphoblastic leukemia?

Answer 5

• 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

Question 6

What conformational changes do activators cause?

Answer 6

Induce rearrangement of mediator to expose surface where pol 2 binds
Cause reaaragment in TFIIB that expose binding surface for pol 2 and F

Question 7

What is the assembly of the PIC stimulated by?

Answer 7

activators, coactivators and chromatin remodellers

Question 8

What can be rate limiting in activation and example?

Answer 8

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

Question 9

What expression is induced when mouse B cells are activated?

Answer 9

TFIIH (catalyses promoter opening nd phos of pol2 ctd on ser5

Question 10

What else can be rate limiting for transcription?

Answer 10

Escape from promoter

Question 11

What stimulates promoter escape and what is it?

Answer 11

P-TEFb

cdk9/cyclin T complex

Question 12

How is promoter escape stimulated?

Answer 12

NELF + DSIF bind pol 2, pausing initiation
P-TEFb phos DSIF causing release of NELF and txn
p-TEFb phos Ser2 on CTD

Question 13

What is NELF and how does it change?

Answer 13

A repressor but phosphor of DSIF converts it to elongation activator

Question 14

Why is txn paused?

Answer 14

Help keep promoter depleted of nucleosomes
Allows rapid induction of genes (after heat shock)
Provides for capping of transcript

Question 15

What does MYC do?

Answer 15

recruits HATs, TBP, TFIIH and P-TEFb to target genes

Can stimulate both pre and post initiation steps in txn

Question 16

What disease was amplification of MYC frequent in?

Answer 16

Hepatocellular carcinoma (HCC) (liver cancer)

Question 17

What is the SEC?

Answer 17

Super elongation complex - Complex of proteins that timulate transcript elongation by pol II

Question 18

How is the SEC involves in leukaemias?

Answer 18

SEC subunits often fused to MLL1 gene through chromosomal translocation
Results in aberrant exp including upreg of HOX genes

Question 19

What is DOT1L?

Answer 19

a methyltransferase in SEC

Question 20

What is DOT1L’s function?

Answer 20

Mono- di-, and trimethylating H3K79 as pol 2 transcribes

Question 21

How is DOT1L involved in treatment of leukaemias?

Answer 21

Required for development driven by MLL1 translocations so inhibitor has entered clinical trials

Question 22

What does EXH2 do?

Answer 22

A histone methyltransferase that repressed txn by trimethylating H3 on lys27

Question 23

How is EZH2 involved in cancers and how is it treated?

Answer 23

In lymphomas it is frequently activated

A drug that inhibits eradicates lympohmas in mice

Question 24

How is DNA methylation involved in cancer?

Answer 24

Silences tumour suppressor genes

Question 25

What on average is the ratio of mRNA to its protein?

Answer 25

1:900